john locke essay concerning human understanding

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John Locke (b. 1632, d. 1704) was a British philosopher, Oxford academic and medical researcher. Locke’s monumental An Essay Concerning Human Understanding (1689) is one of the first great defenses of modern empiricism and concerns itself with determining the limits of human understanding in respect to a wide spectrum of topics. It thus tells us in some detail what one can legitimately claim to know and what one cannot. Locke’s association with Anthony Ashley Cooper (later the First Earl of Shaftesbury) led him to become successively a government official charged with collecting information about trade and colonies, economic writer, opposition political activist, and finally a revolutionary whose cause ultimately triumphed in the Glorious Revolution of 1688. Among Locke’s political works he is most famous for The Second Treatise of Government in which he argues that sovereignty resides in the people and explains the nature of legitimate government in terms of natural rights and the social contract. He is also famous for calling for the separation of Church and State in his Letter Concerning Toleration . Much of Locke’s work is characterized by opposition to authoritarianism. This is apparent both on the level of the individual person and on the level of institutions such as government and church. For the individual, Locke wants each of us to use reason to search after truth rather than simply accept the opinion of authorities or be subject to superstition. He wants us to proportion assent to propositions to the evidence for them. On the level of institutions it becomes important to distinguish the legitimate from the illegitimate functions of institutions and to make the corresponding distinction for the uses of force by these institutions. Locke believes that using reason to try to grasp the truth, and determine the legitimate functions of institutions will optimize human flourishing for the individual and society both in respect to its material and spiritual welfare. This in turn, amounts to following natural law and the fulfillment of the divine purpose for humanity.

1.1 Locke’s Life up to His Meeting with Lord Ashley in 1666

1.2 locke and lord shaftesbury 1666 to 1688, 1.3 the end of locke’s life 1689–1704, 2.2 book ii, 2.3 book iii, 2.4 book iv, 2.5 knowledge and probability, 2.6 reason, faith and enthusiasm, 3. locke’s major works on education, 4.1 the second treatise of government, 4.2 human nature and god’s purposes, 4.3 of war and slavery, 4.4 of property, 4.5 the social contract theory, 4.6 the function of civil government, 4.7 rebellion and regicide, 5. locke and religious toleration, primary sources, secondary sources, other internet resources, related entries, 1. historical background and locke’s life.

John Locke (1632–1704) was one of the greatest philosophers in Europe at the end of the seventeenth century. Locke grew up and lived through one of the most extraordinary centuries of English political and intellectual history. It was a century in which conflicts between Crown and Parliament and the overlapping conflicts between Protestants, Anglicans and Catholics swirled into civil war in the 1640s. With the defeat and death of Charles I, there began a great experiment in governmental institutions including the abolishment of the monarchy, the House of Lords and the Anglican church, and the establishment of Oliver Cromwell’s Protectorate in the 1650s. The collapse of the Protectorate after the death of Cromwell was followed by the Restoration of Charles II—the return of the monarchy, the House of Lords and the Anglican Church. This period lasted from 1660 to 1688. It was marked by continued conflicts between King and Parliament and debates over religious toleration for Protestant dissenters and Catholics. This period ends with the Glorious Revolution of 1688 in which James II was driven from England and replaced by William of Orange and his wife Mary. The final period during which Locke lived involved the consolidation of power by William and Mary, and the beginning of William’s efforts to oppose the domination of Europe by the France of Louis XIV, which later culminated in the military victories of John Churchill—the Duke of Marlborough.

Locke was born in Wrington to Puritan parents of modest means. His father was a country lawyer who served in a cavalry company on the Puritan side in the early stages of the English Civil War. His father’s commander, Alexander Popham, became the local MP, and it was his patronage which allowed the young John Locke to gain an excellent education. In 1647 Locke went to Westminster School in London.

From Westminster school he went to Christ Church, Oxford, in the autumn of 1652 at the age of twenty. As Westminster school was the most important English school, so Christ Church was the most important Oxford college. Education at Oxford was medieval. Locke, like Hobbes before him, found the Aristotelian philosophy he was taught at Oxford of little use. There was, however, more at Oxford than Aristotle. The new experimental philosophy had arrived. John Wilkins, Cromwell’s brother in law, had become Warden of Wadham College. The group around Wilkins was the nucleus of what was to become the English Royal Society. The Society grew out of informal meetings and discussion groups and moved to London after the Restoration and became a formal institution in the 1660s with charters from Charles II. The Society saw its aims in contrast with the Scholastic/Aristotelian traditions that dominated the universities. The program was to study nature rather than books. [ 1 ] Many of Wilkins associates were people interested in pursuing medicine by observation rather than the reading of classic texts. Bacon’s interest in careful experimentation and the systematic collection of facts from which generalizations could be made was characteristic of this group. One of Locke’s friends from Westminster school, Richard Lower, introduced Locke to medicine and the experimental philosophy being pursued by the virtuosi at Wadham.

Locke received his B.A. in February 1656. His career at Oxford, however, continued beyond his undergraduate days. In June of 1658, Locke qualified as a Master of Arts and was elected a Senior Student of Christ Church College. The rank was equivalent to a Fellow at any of the other colleges, but was not permanent. Locke had yet to determine what his career was to be. Locke was elected Lecturer in Greek at Christ Church in December of 1660 and he was elected Lecturer in Rhetoric in 1663. At this point, Locke needed to make a decision. The statutes of Christ Church laid it down that fifty five of the senior studentships should be reserved for men in orders or reading for orders. Only five could be held by others, two in medicine, two in law and one in moral philosophy. Thus, there was good reason for Locke to become a clergyman. Since his graduation Locke had been studying medicine. Locke decided to become a doctor.

John Wilkins had left Oxford with the Restoration of Charles II. The new leader of the Oxford scientific group was Robert Boyle. He was also Locke’s scientific mentor. Boyle (with the help of his astonishing assistant Robert Hooke) built an air pump which led to the formulation of Boyle’s law and devised a barometer as a weather indicator. The work on the air pump led to a controversy with Thomas Hobbes because Boyle’s explanations of the working of the air pump were incompatible with Hobbes’ micro-corpuscular theory. This controversy continued for ten years. Boyle was, however, most influential as a theorist. He was a mechanical philosopher who treated the world as reducible to matter in motion. But he had no micro-corpuscular account of the air.

Locke read Boyle before he read Descartes. When he did read Descartes, he saw the great French philosopher as providing a viable alternative to the sterile Aristotelianism he had been taught at Oxford. In writing An Essay Concerning Human Understanding Locke adopted Descartes’ ‘way of ideas’; though it is transformed so as to become an organic part of Locke’s philosophy. Still, while admiring Descartes, Locke’s involvement with the Oxford scientists gave him a perspective that made him critical of the rationalist elements in Descartes’ philosophy.

In the Epistle to the Reader at the beginning of the Essay Locke remarks:

The commonwealth of learning is not at this time without master-builders, whose mighty designs, in advancing the sciences, will leave lasting monuments to the admiration of posterity: but everyone must not hope to be a Boyle or a Sydenham; and in an age that produces such masters as the great Huygenius and the incomparable Mr. Newton, with some others of that strain, it is ambition enough to be employed as an under-labourer in clearing the ground a little, and removing some of the rubbish that lies in the way to knowledge …. (N: 9–10; all quotations are from the Nidditch edition of An Essay Concerning Human Understanding [N])

Locke knew all of these men and their work. Locke, Boyle and Newton were all founding or early members of the English Royal Society. It is from Boyle that Locke learned about atomism (or the corpuscular hypothesis) and it is from Boyle’s book The Origin of Forms and Qualities that Locke took the language of primary and secondary qualities. Sydenham was an English physician and Locke did medical research with him. Sydenham championed careful observation of disease and rejected appeal to underlying causes. Both Boyle and Newton did work on colors that did not involve micro-corpuscular explanations. Locke read Newton’s Principia Mathematica Philosophiae Naturalis while in exile in Holland, and consulted Huygens as to the soundness of its mathematics. Locke and Newton became friends after Locke’s return from Holland in 1688. It may be that in referring to himself as an ‘under-labourer’, Locke is not only displaying a certain literary modesty, he is contrasting the positive discoveries of these men, with his own attempt to show the inadequacies of the Aristotelian and Scholastic and to some degree the Cartesian philosophies. There are, however, many aspects of Locke’s project to which this image of an under-labourer does not do justice (see Jolley 1999: 15–17). While the corpuscular philosophy and Newton’s discoveries clearly influenced Locke, it is the Baconian program of producing natural histories that Locke makes reference to when he talks about the Essay in the Introduction. He writes:

It shall suffice to my present Purpose, to consider the discerning Faculties of a Man, as they are employ’d about the Objects, which they have to do with: and I shall imagine that I have not wholly misimploy’d my self in the Thoughts I shall have on this Occasion, if in this Historical, Plain Method, I can give any Account of the Ways, whereby our Understanding comes to attain those Notions of Things, and can set down any Measure of the Certainty of our Knowledge…. (I.1.2, N: 43–4—the three numbers, are book, chapter and section numbers respectively, followed by the page number in the Nidditch edition)

The ‘Historical, Plain Method’ is apparently to give a genetic account of how we come by our ideas. Presumably this will reveal the degree of certainty of the knowledge based on such ideas. Locke’s own active involvement with the scientific movement was largely through his informal studies of medicine. Dr. David Thomas was his friend and collaborator. Locke and Thomas had a laboratory in Oxford which was very likely, in effect, a pharmacy. In 1666 Lord Ashley, one of the richest men in England, came to Oxford in order to drink some medicinal waters there. He had asked Dr. Thomas to provide them. Thomas had to be out of town and asked Locke to see that the water was delivered. As a result of this encounter, Ashley invited Locke to come to London as his personal physician. In 1667 Locke did move to London becoming not only Lord Ashley’s personal physician, but secretary, researcher, political operative and friend. Living with him Locke found himself at the very heart of English politics in the 1670s and 1680s.

Locke’s chief work while living at Lord Ashley’s residence, Exeter House, in 1668 was as Ashley’s physician. Locke used his medical training to organize a successful operation on Ashley. This was perhaps the most carefully documented operation in the 17th century. Locke consulted doctors across the country to determine what the best practices were for this operation and made cleanliness a priority. In doing so he saved his patron’s life and thus changed English history.

Locke had a number of other jobs. He worked as secretary of the Board of Trade and Plantations and Secretary to the Lords Proprietors of the Carolinas. Lord Ashley was one of the advocates of the view that England would prosper through trade and that colonies could play an important role in promoting trade. Ashley persuaded Charles II to create a Board of Trade and Plantations to collect information about trade and colonies, and Locke became its secretary. In his capacity as the secretary of the Board of Trade Locke was the collection point for information from around the globe about trade and colonies for the English government. Among Ashley’s commercial projects was an effort to found colonies in the Carolinas. In his capacity as the secretary to the Lords Proprietors, Locke was involved in the writing of the fundamental constitution of the Carolinas. There is some controversy about the extent of Locke’s role in writing the constitution. [ 2 ] In addition to issues about trade and colonies, Locke was involved through Shaftesbury in other controversies about public policy. There was a monetary crisis in England involving the value of money, and the clipping of coins. Locke wrote papers for Lord Ashley on economic matters, including the coinage crisis.

While living in London at Exeter House, Locke continued to be involved in philosophical discussions. He tells us that:

Were it fit to trouble thee with the history of this Essay, I should tell thee, that five or six friends meeting at my chamber, and discoursing on a subject very remote from this, found themselves quickly at a stand, by the difficulties that rose on every side. After we had awhile puzzled ourselves, without coming any nearer a resolution of those doubts which perplexed us, it came into my thoughts that we took a wrong course; and that before we set ourselves upon inquiries of that nature, it was necessary to examine our own abilities, and see what objects our understandings were, or were not, fitted to deal with. This I proposed to the company, who all readily assented; and thereupon it was agreed that this should be our first inquiry. Some hasty and undigested thoughts, on a subject I had never before considered, which I set down against our next meeting, gave the first entrance into this Discourse; which having been thus begun by chance, was continued by intreaty; written by incoherent parcels; and after long intervals of neglect, resumed again, as my humour or occasions permitted; and at last, in a retirement where an attendance on my health gave me leisure, it was brought into that order thou now seest it. (Epistle to the Reader, N: 7)

James Tyrrell, one of Locke’s friends was at that meeting. He recalls the discussion being about the principles of morality and revealed religion (Cranston 1957: 140–1). Thus the Oxford scholar and medical researcher came to begin the work which was to occupy him off and on over the next twenty years.

In 1674 after Shaftesbury had left the government, Locke went back to Oxford, where he acquired the degree Bachelor of medicine, and a license to practice medicine, and then went to France (Cranston 1957: 160). In France Locke went from Calais to Paris, Lyons and on to Montpellier, where he spent the next fifteen months. Much of Locke’s time was spent learning about Protestantism in France. The Edict of Nantes (promulgated by Henry IV in 1598) was in force, and so there was a degree of religious toleration in France. Louis XIV was to revoke the edict in 1685 and French Protestants were then killed while some 400,000 went into exile.

While Locke was in France, Shaftesbury’s fortunes fluctuated. In 1676 Shaftesbury was imprisoned in the tower. His imprisonment lasted for a year. In 1678, after the mysterious murder of a London judge, informers (most notably Titus Oates) started coming forward to reveal a supposed Catholic conspiracy to assassinate the King and put his brother on the throne. This whipped up public anti-Catholic frenzy. Though Shaftesbury had not fabricated the conspiracy story, nor did he prompt Oates to come forward, he did exploit the situation to the advantage of his party. In the public chaos surrounding the sensational revelations, Shaftesbury organized an extensive party network, exercised great control over elections, and built up a large parliamentary majority. His strategy was to secure the passage of an Exclusion bill that would prevent Charles II’s openly Catholic brother from becoming King. Although the Exclusion bill passed in the Commons it was rejected in the House of Lords because of the King’s strong opposition to it. As the panic over the Popish plot receded, Shaftesbury was left without a following or a cause. Shaftesbury was seized on July 21, 1681 and again put in the tower. He was tried on trumped-up charges of treason but acquitted by a London grand jury (filled with his supporters) in November.

At this point some of the Country Party leaders began plotting an armed insurrection which, had it come off, would have begun with the assassination of Charles and his brother on their way back to London from the races at Newmarket. The chances of such a rising occurring were not as good as the plotters supposed. Memories of the turmoil of the civil war were still relatively fresh. Eventually Shaftesbury, who was moving from safe house to safe house, gave up and fled to Holland in November 1682. He died there in January 1683. Locke stayed in England until the Rye House Plot (named after the house from which the plotters were to fire upon the King and his brother) was discovered in June of 1683. Locke left for the West country to put his affairs in order the very week the plot was revealed to the government and by September he was in exile in Holland. [ 3 ]

While in exile, Locke finished An Essay Concerning Human Understanding and published a fifty-page advanced notice of it in French. (This was to provide the intellectual world on the continent with most of their information about the Essay until Pierre Coste’s French translation appeared in 1704.) He also wrote and published his Epistola de Tolerentia in Latin. Richard Ashcraft, in his Revolutionary Politics and Locke’s Two Treatises of Government (1986) suggests that while in Holland, Locke was not only finishing An Essay Concerning Human Understanding and nursing his health, he was closely associated with the English revolutionaries in exile. The English government was much concerned with this group. They tried to get a number of them, including Locke, extradited to England. Locke’s studentship at Oxford was taken away from him. In the meanwhile, the English intelligence service infiltrated the rebel group in Holland and effectively thwarted their efforts—at least for a while. While Locke was living in exile in Holland, Charles II died on Feb. 6, 1685, and was succeeded by his brother, who became James II of England. Soon after this, the rebels in Holland sent a force of soldiers under the Duke of Monmouth to England to try to overthrow James II. The revolt was crushed, and Monmouth was captured and executed (Ashcraft 1986). For a meticulous, if cautious review, of the evidence concerning Locke’s involvement with the English rebels in exile see Roger Woolhouse’s Locke: A Biography (2007).

Ultimately, however, the rebels were successful. James II alienated most of his supporters, and William of Orange was invited to bring a Dutch force to England. After William’s army landed, James II, realizing that he could not mount an effective resistance, fled the country to exile in France. This became known as the Glorious Revolution of 1688. It is a watershed in English history. For it marks the point at which the balance of power in the English government passed from the King to the Parliament. Locke returned to England in February 1689.

After his return from exile, Locke published An Essay Concerning Human Understanding and The Two Treatises of Government . In addition, Popple’s translation of Locke’s A Letter Concerning Toleration was also published. It is worth noting that the Two Treatises and the Letter Concerning Toleration were published anonymously. Locke took up residence in the country at Oates in Essex, the home of Sir Francis and Lady Masham (Damaris Cudworth). Locke had met Damaris Cudworth in 1682 and became involved intellectually and romantically with her. She was the daughter of Ralph Cudworth, the Cambridge Platonist, and a philosopher in her own right. After Locke went into exile in Holland in 1683, she married Sir Francis Masham. Locke and Lady Masham remained good friends and intellectual companions to the end of Locke’s life. During the remaining years of his life, Locke oversaw four more editions of the Essay and engaged in controversies over the Essay most notably in a series of published letters with Edward Stillingfleet, Bishop of Worcester. In a similar way, Locke defended the Letter Concerning Toleration against a series of attacks. He wrote The Reasonableness of Christianity and Some Thoughts on Education during this period as well.

Nor was Locke finished with public affairs. In 1696 the Board of Trade was revived. Locke played an important part in its revival and served as the most influential member on it until 1700. The new Board of Trade had administrative powers and was, in fact, concerned with a wide range of issues, from the Irish wool trade and the suppression of piracy, to the treatment of the poor in England and the governance of the colonies. It was, in Peter Laslett’s phrase “the body which administered the United States before the American Revolution” (Laslett 1954 [1990: 127]). During these last eight years of his life, Locke was asthmatic, and he suffered so much from it that he could only bear the smoke of London during the four warmer months of the year. Locke plainly engaged in the activities of the Board out of a strong sense of patriotic duty. After his retirement from the Board of Trade in 1700, Locke remained in retirement at Oates until his death on Sunday 28 October 1704.

2. The Limits of Human Understanding

Locke is often classified as the first of the great English empiricists (ignoring the claims of Bacon and Hobbes). This reputation rests on Locke’s greatest work, the monumental An Essay Concerning Human Understanding . Locke explains his project in several places. Perhaps the most important of his goals is to determine the limits of human understanding. Locke writes:

For I thought that the first Step towards satisfying the several Enquiries, the Mind of Man was apt to run into, was, to take a Survey of our own Understandings, examine our own Powers, and see to what Things they were adapted. Till that was done, I suspected that we began at the wrong end, and in vain sought for Satisfaction in a quiet and secure Possession of Truths, that most concern’d us whilst we let loose our Thoughts into the vast Ocean of Being , as if all the boundless Extent, were the natural and undoubted Possessions of our Understandings, wherein there was nothing that escaped its Decisions, or that escaped its Comprehension. Thus Men, extending their Enquiries beyond their Capacities, and letting their Thoughts wander into those depths where they can find no sure Footing; ’tis no Wonder, that they raise Questions and multiply Disputes, which never coming to any clear Resolution, are proper to only continue and increase their Doubts, and to confirm them at last in a perfect Skepticism. Wheras were the Capacities of our Understanding well considered, the Extent of our Knowledge once discovered, and the Horizon found, which sets the boundary between the enlightened and the dark Parts of Things; between what is and what is not comprehensible by us, Men would perhaps with less scruple acquiesce in the avow’d Ignorance of the one; and employ their Thoughts and Discourse, with more Advantage and Satisfaction in the other. (I.1.7, N: 47)

Some philosophers before Locke had suggested that it would be good to find the limits of the Understanding, but what Locke does is to carry out this project in detail. In the four books of the Essay Locke considers the sources and nature of human knowledge. Book I argues that we have no innate knowledge. (In this he resembles Berkeley and Hume, and differs from Descartes and Leibniz.) So, at birth, the human mind is a sort of blank slate on which experience writes. In Book II Locke claims that ideas are the materials of knowledge and all ideas come from experience. The term ‘idea’, Locke tells us “…stands for whatsoever is the Object of the Understanding, when a man thinks” (I.1.8, N: 47). Experience is of two kinds, sensation and reflection. One of these—sensation—tells us about things and processes in the external world. The other—reflection—tells us about the operations of our own minds. Reflection is a sort of internal sense that makes us conscious of the mental processes we are engaged in. Some ideas we get only from sensation, some only from reflection and some from both.

Locke has an atomic or perhaps more accurately a corpuscular theory of ideas. [ 4 ] There is, that is to say, an analogy between the way atoms or corpuscles combine into complexes to form physical objects and the way ideas combine. Ideas are either simple or complex. We cannot create simple ideas, we can only get them from experience. In this respect the mind is passive. Once the mind has a store of simple ideas, it can combine them into complex ideas of a variety of kinds. In this respect the mind is active. Thus, Locke subscribes to a version of the empiricist axiom that there is nothing in the intellect that was not previously in the senses—where the senses are broadened to include reflection. Book III deals with the nature of language, its connections with ideas and its role in knowledge. Book IV, the culmination of the previous reflections, explains the nature and limits of knowledge, probability, and the relation of reason and faith. Let us now consider the Essay in some detail.

At the beginning of An Essay Concerning Human Understanding Locke says that since his purpose is “to enquire into the Original, Certainty and Extent of human knowledge, together with the grounds and degrees of Belief, Opinion and Assent” he is going to begin with ideas—the materials out of which knowledge is constructed. His first task is to “enquire into the Original of these Ideas…and the ways whereby the Understanding comes to be furnished with them” (I.1.3, N: 44). The role of Book I of the Essay is to make the case that being innate is not a way in which the understanding is furnished with principles and ideas. Locke treats innateness as an empirical hypothesis and argues that there is no good evidence to support it.

Locke describes innate ideas as “some primary notions…Characters as it were stamped upon the Mind of Man, which the Soul receives in its very first Being; and brings into the world with it” (I.2.1, N: 48). In pursuing this enquiry, Locke rejects the claim that there are speculative innate principles (I.2), practical innate moral principles (I.3) or that we have innate ideas of God, identity or impossibility (I.4). Locke rejects arguments from universal assent and attacks dispositional accounts of innate principles. Thus, in considering what would count as evidence from universal assent to such propositions as “What is, is” or “It is impossible for the same thing to be and not to be” he holds that children and idiots should be aware of such truths if they were innate but that they “have not the least apprehension or thought of them”. Why should children and idiots be aware of and able to articulate such propositions? Locke says:

It seems to me a near Contradiction to say that there are truths imprinted on the Soul, which it perceives or understands not; imprinting if it signify anything, being nothing else but the making certain Truths to be perceived. (I.2.5, N: 49)

So, Locke’s first point is that if propositions were innate they should be immediately perceived—by infants and idiots (and indeed everyone else)—but there is no evidence that they are. Locke then proceeds to attack dispositional accounts that say, roughly, that innate propositions are capable of being perceived under certain circumstances. Until these circumstances come about the propositions remain unperceived in the mind. With the advent of these conditions, the propositions are then perceived. Locke gives the following argument against innate propositions being dispositional:

For if any one [proposition] may [be in the mind but not be known]; then, by the same Reason, all Propositions that are true, and the Mind is ever capable of assenting to, may be said to be in the Mind, and to be imprinted: since if any one can be said to be in the Mind, which it never yet knew, it must be only because it is capable of knowing it; and so the Mind is of all Truths it ever shall know. (I.2.5, N: 50)

The essence of this argument and many of Locke’s other arguments against dispositional accounts of innate propositions is that such dispositional accounts do not provide an adequate criterion for distinguishing innate propositions from other propositions that the mind may come to discover. Thus, even if some criterion is proposed, it will turn out not to do the work it is supposed to do.

When Locke turns from speculative principles to the question of whether there are innate practical moral principles, many of the arguments against innate speculative principles continue to apply, but there are some additional considerations. Practical principles, such as the Golden Rule, are not self-evident in the way such speculative principles as “What is, is” are. Thus, one can clearly and sensibly ask reasons for why one should hold the Golden Rule true or obey it (I.3.4, N: 68). There are substantial differences between people over the content of practical principles. Thus, they are even less likely candidates to be innate propositions or to meet the criterion of universal assent. In the fourth chapter of Book I, Locke raises similar points about the ideas which compose both speculative and practical principles. The point is that if the ideas that are constitutive of the principles are not innate, this gives us even more reason to hold that the principles are not innate. He examines the ideas of identity, impossibility and God to make these points.

In Book I Locke says little about who holds the doctrine of innate principles that he is attacking. For this reason he has sometimes been accused of attacking straw men. John Yolton has persuasively argued (Yolton 1956) that the view that innate ideas and principles were necessary for the stability of religion, morality and natural law was widespread in England in the seventeenth century, and that in attacking both the naive and the dispositional account of innate ideas and innate principles, Locke is attacking positions which were widely held and continued to be held after the publication of the Essay . Thus, the charge that Locke’s account of innate principles is made of straw, is not a just criticism. But there are also some important connections with particular philosophers and schools that are worth noting and some points about innate ideas and inquiry.

At I. 4. 24. Locke tells us that the doctrine of innate principles once accepted “eased the lazy from the pains of search” and that the doctrine is an inquiry stopper that is used by those who “affected to be Masters and Teachers” to illegitimately gain control of the minds of their students. Locke rather clearly has in mind the Aristotelians and scholastics at the universities. Thus Locke’s attack on innate principles is connected with his anti-authoritarianism. It is an expression of his view of the importance of free and autonomous inquiry in the search for truth. Ultimately, Locke holds, this is the best road to knowledge and happiness. Locke, like Descartes, is tearing down the foundations of the old Aristotelian scholastic house of knowledge. But while Descartes focused on the empiricism at the foundation of the structure, Locke is focusing on the claims that innate ideas provide its first principles. The attack on innate ideas is thus the first step in the demolition of the scholastic model of science and knowledge. Ironically, it is also clear from II.1.9. that Locke sees Descartes’ claim that his essence is to be a thinking thing as entailing a doctrine of innate ideas and principles.

In Book II of the Essay , Locke gives his positive account of how we acquire the materials of knowledge. Locke distinguishes a variety of different kinds of ideas in Book II. Locke holds that the mind is a tabula rasa or blank sheet until experience in the form of sensation and reflection provide the basic materials—simple ideas—out of which most of our more complex knowledge is constructed. While the mind may be a blank slate in regard to content, it is plain that Locke thinks we are born with a variety of faculties to receive and abilities to manipulate or process the content once we acquire it. Thus, for example, the mind can engage in three different types of action in putting simple ideas together. The first of these kinds of action is to combine them into complex ideas. Complex ideas are of two kinds, ideas of substances and ideas of modes. Substances are independent existences. Beings that count as substances include God, angels, humans, animals, plants and a variety of constructed things. Modes are dependent existences. These include mathematical and moral ideas, and all the conventional language of religion, politics and culture. The second action which the mind performs is the bringing of two ideas, whether simple or complex, by one another so as to take a view of them at once, without uniting them. This gives us our ideas of relations (II.12.1, N: 163). The third act of the mind is the production of our general ideas by abstraction from particulars, leaving out the particular circumstances of time and place, which would limit the application of an idea to a particular individual. In addition to these abilities, there are such faculties as memory which allow for the storing of ideas.

Having set forth the general machinery of how simple and complex ideas of substances, modes, relations, and so forth are derived from sensation and reflection, Locke also explains how a variety of particular kinds of ideas, such as the ideas of solidity, number, space, time, power, identity, and moral relations arise from sensation and reflection. Several of these are of particular interest. Locke’s chapter on power gives rise to a discussion of free will and voluntary action (see the entry on Locke on freedom ). Locke also made a number of interesting claims in the philosophy of mind. He suggested, for example, that for all we know, God could as easily add the powers of perception and thought to matter organized in the right way as he could add those powers to an immaterial substance which would then be joined to matter organized in the right way. His account of personal identity in II. xxvii was revolutionary. (See the entry on Locke on personal identity) . Both of these topics and related ones are treated in the supplementary document: Some Interesting Issues in Locke’s Philosophy of Mind

In what follows, we focus on some central issues in Locke’s account of physical objects. (See also the entry Locke’s philosophy of science , which pursues a number of topics related to Locke’s account of physical objects that are of considerable importance but largely beyond the scope of this general account of Locke’s philosophy.) These include Locke on knowledge in natural philosophy, the limitations of the corpuscular philosophy and Locke’s relation to Newton.

Locke offers an account of physical objects based on the mechanical philosophy and the corpuscular hypothesis. The adherents of the mechanical philosophy held that all material phenomena can be explained by matter in motion and the impact of one body on another. They viewed matter as passive. They rejected the “occult qualities” and “causation at a distance” of the Aristotelian and Scholastic philosophy. Robert Boyle’s corpuscularian hypothesis treated the material world as made up of particles. Some corpuscularians held that corpuscles could be further divided and that the universe was full of matter with no void space. Atomists, on the other hand, held that the particles were indivisible and that the material world is composed of atoms and the void or empty space in which the atoms move. Locke was an atomist.

Atoms have properties. They are extended, they are solid, they have a particular shape and they are in motion or rest. They combine together to produce the familiar stuff and physical objects, the gold and the wood, the horses and violets, the tables and chairs of our world. These familiar things also have properties. They are extended, solid, have a particular shape, and are in motion and at rest. In addition to these properties that they share with the atoms that compose them, they have other properties such as colors, smells, tastes that they get by standing in relation to perceivers. The distinction between these two kinds of properties goes back to the Greek atomists. It is articulated by Galileo and Descartes as well as Locke’s mentor Robert Boyle.

Locke makes this distinction in Book II Chapter 8 of the Essay and using Boyle’s terminology calls the two different classes of properties the primary and secondary qualities of an object. This distinction is made by both of the main branches of the mechanical philosophy of the seventeenth and early eighteenth century. Both the Cartesian plenum theorists, who held that the world was full of infinitely divisible matter and that there was no void space, and the atomists such as Gassendi, who held that there were indivisible atoms and void space in which the atoms move, made the distinction between these two classes of properties. Still, the differences between these two branches of the mechanical philosophy affect their account of primary qualities. In the chapter on Solidity (II.4) Locke rejects the Cartesian definition of body as simply extended and argues that bodies are both extended and impenetrable or solid. The inclusion of solidity in Locke’s account of bodies and of primary qualities distinguishes them from the void space in which they move.

The primary qualities of an object are properties which the object possesses independent of us—such as occupying space, being either in motion or at rest, having solidity and texture. The secondary qualities are powers in bodies to produce ideas in us like color, taste, smell and so on that are caused by the interaction of our particular perceptual apparatus with the primary qualities of the object. Our ideas of primary qualities resemble the qualities in the object, while our ideas of secondary qualities do not resemble the powers that cause them. Locke also distinguishes a second class of secondary properties that are the powers that one substance has to effect another, e.g. the power of a fire to melt a piece of wax.

There has been considerable scholarly debate concerning the details of Locke’s account of the distinction. Among the issues are which qualities Locke assigns to each of the two categories. Locke gives several lists. Another issue is what the criterion is for putting a quality in one list rather than another. Does Locke hold that all the ideas of secondary qualities come to us by one sense while the ideas of primary qualities come to us through two or is Locke not making the distinction in this way? Another issue is whether there are only primary qualities of atoms or whether compounds of atoms also have primary qualities. And while Locke claims our ideas of primary qualities resemble the primary qualities in objects, and the ideas of secondary qualities do not resemble their causes in the object, what does ‘resemble’ mean in this context? Related to this issue is how we are supposed to know about particles that we cannot sense. It seems clear that Locke holds that there are certain analogies between the middle sized macroscopic objects we encounter in the world, e.g. porphyry and manna for example, and the particles that compose these things. Maurice Mandelbaum called this process ‘transdiction’. These analogies allow us to say certain things about the nature of particles and primary and secondary qualities. For example we can infer that atoms are solid and that heat is a greater rate of motion of atoms while cold is a slower motion. But these analogies may not get us very far in grasping the necessary connections between qualities in nature. Yet another issue is whether Locke sees the distinction as reductionistic. If what we mean by reductionistic here is that only the primary qualities are real and these explain the secondary qualities then there does not seem to be a clear answer. Secondary qualities surely are nothing more than certain primary qualities that affect us in certain ways. This seems to be reductionistic. But on Locke’s account of “real ideas” in II.30 both the ideas of primary and secondary qualities count as real. And while Locke holds that our ideas of secondary qualities are caused by primary qualities, in certain important respects the primary qualities do not explain them. Locke holds that we cannot even conceive how the size, figure and motion of particles could cause any sensation in us. So, knowing the size, figure and motion of the particles would be of no use to us in this regard (see IV.3.11–40, N: 544–546).

Locke probably holds some version of the representational theory of perception, though some scholars dispute this. On such a theory what the mind immediately perceives are ideas, and the ideas are caused by and represent the objects which cause them. Thus perception is a triadic relation, rather than simply being a dyadic relation between an object and a perceiver. Such a dyadic relational theory is often called naive realism because it suggests that the perceiver is directly perceiving the object, and naive because this view is open to a variety of serious objections. Some versions of the representational theory are open to serious objections as well. If, for example, one treats ideas as things, then one can imagine that because one sees ideas, the ideas actually block one from seeing things in the external world. The idea would be like a picture or painting. The picture would copy the original object in the external world, but because our immediate object of perception is the picture we would be prevented from seeing the original just as standing in front of a painting on an easel might prevent us from seeing the person being painted. Thus, this is sometimes called the picture/original theory of perception. Alternatively, Jonathan Bennett called it “the veil of perception” to emphasize that ‘seeing’ the ideas prevents us from seeing the external world. One philosopher who arguably held such a view was Nicholas Malebranche, a follower of Descartes. Antoine Arnauld, by contrast, while believing in the representative character of ideas, is a direct realist about perception. Arnauld engaged in a lengthy controversy with Malebranche, and criticized Malebranche’s account of ideas. Locke follows Arnauld in his criticism of Malebranche on this point (Locke, 1823, Vol. IX: 250). Yet Berkeley attributed the veil of perception interpretation of the representational theory of perception to Locke as have many later commentators including Bennett. A.D. Woozley puts the difficulty of doing this succinctly:

…it is scarcely credible both that Locke should be able to see and state so clearly the fundamental objection to the picture-original theory of sense perception, and that he should have held the same theory himself. (Woozley 1964: 27)

Just what Locke’s account of perception involves, is still a matter of scholarly debate. A review of this issue at a symposium including John Rogers, Gideon Yaffe, Lex Newman, Tom Lennon, and Vere Chappell at a meeting of the Pacific Division of the American Philosophical Association in 2003 and later expanded and published in the Pacific Philosophical Quarterly (2004, volume 85, issue 3) found most of the symposiasts holding the view that Locke holds a representative theory of perception but that he is not a skeptic about the external world in the way that the veil of perception doctrine might suggest.

Another issue that has been a matter of controversy since the first publication of the Essay is what Locke means by the term ‘substance’. The primary/secondary quality distinction gets us a certain ways in understanding physical objects, but Locke is puzzled about what underlies or supports the primary qualities themselves. He is also puzzled about what material and immaterial substances might have in common that would lead us to apply the same word to both. These kinds of reflections led him to the relative and obscure idea of substance in general. This is an “I know not what” which is the support of qualities which cannot subsist by themselves. We experience properties appearing in regular clumps, but we must infer that there is something that supports or perhaps ‘holds together’ those qualities. For we have no experience of that supporting substance. It is clear that Locke sees no alternative to the claim that there are substances supporting qualities. He does not, for example, have a theory of tropes (tropes are properties that can exist independently of substances) which he might use to dispense with the notion of substance. (In fact, he may be rejecting something like a theory of tropes when he rejects the Aristotelian doctrine of real qualities and insists on the need for substances.) He is thus not at all a skeptic about ‘substance’ in the way that Hume is. But, it is also quite clear that he is regularly insistent about the limitations of our ideas of substances. Bishop Stillingfleet accused Locke of putting substance out of the reasonable part of the world. But Locke is not doing that.

Since Berkeley, Locke’s doctrine of the substratum or substance in general has been attacked as incoherent. It seems to imply that we have a particular without any properties, and this seems like a notion that is inconsistent with empiricism. We have no experience of such an entity and so no way to derive such an idea from experience. Locke himself acknowledges this point (I.4.18, N: 95). In order to avoid this problem, Michael Ayers has proposed that we must understand the notions of ‘substratum’ and ‘substance in general’ in terms of Locke’s distinction between real and nominal essences and particularly his doctrine of real essences developed in Book III of the Essay rather than as a separate problem from that of knowing real essences. The real essence of a material thing is its atomic constitution. This atomic constitution is the causal basis of all the observable properties of the thing, from which we create nominal essences. Were the real essence known, all the observable properties could be deduced from it. Locke claims that the real essences of material things are quite unknown to us. Locke’s concept of substance in general is also a ‘something I know not what’. Thus, on Ayers’ interpretation ‘substance in general’ means something like ‘whatever it is that supports qualities’ while the real essence means ‘this particular atomic constitution that explains this set of observable qualities’. Thus, Ayers wants to treat the unknown substratum as picking out the same thing as the real essence—thus eliminating the need for particulars without properties. This proposed way of interpreting Locke has been criticized by scholars both because of a lack of textural support, and on the stronger grounds that it conflicts with some things that Locke does say (see Jolley 1999: 71–3). As we have reached one of the important concepts in Book III, let us turn to that Book and Locke’s discussion of language.

Locke devotes Book III of An Essay Concerning Human Understanding to language. This is a strong indication that Locke thinks issues about language were of considerable importance in attaining knowledge. At the beginning of the Book he notes the importance of abstract general ideas to knowledge. These serve as sorts under which we rank all the vast multitude of particular existences. Thus, abstract ideas and classification are of central importance in Locke’s discussion of language and its importance for knowledge. Without general terms and classes we would be faced with the impossible task of trying to know a vast world of particulars.

There is a clear connection between Books II and III in that Locke claims that words stand for ideas. In his discussion of language Locke distinguishes words according to the categories of ideas established in Book II of the Essay . So there are ideas of substances, simple modes, mixed modes, relations and so on. It is in this context that Locke makes the distinction between real and nominal essences noted above. Perhaps because of his focus on the role that kind terms play in classification, Locke pays vastly more attention to nouns than to verbs. Locke recognizes that not all words relate to ideas. There are also the many particles, words that “…signify the connexion that the Mind gives to Ideas, or Propositions, one with another” (II.7.1, N: 471). Still, it is the relation of words and ideas that gets most of Locke’s attention in Book III.

Norman Kretzmann calls the claim that “words in their primary or immediate signification signify nothing but the ideas in the mind of him that uses them ” (III.2.2) “Locke’s main semantic thesis” (see Kretzmann 1968:179). This thesis has often been criticized as a classic blunder in semantic theory. Thus Mill, for example, wrote, “When I say, ‘the sun is the cause of the day’, I do not mean that my idea of the sun causes or excites in me the idea of day” (Mill 1843: bk 1, ch. 2, § 1). This criticism of Locke’s account of language parallels the “veil of perception” critique of his account of perception and suggests that Locke is not distinguishing the meaning of a word from its reference. Kretzmann, however, argues persuasively that Locke distinguishes between meaning and reference and that ideas provide the meaning but not the reference of words. Thus, the line of criticism represented by the quotation from Mill is ill founded.

In addition to the kinds of ideas noted above, there are also particular and abstract ideas. Particular ideas have in them the ideas of particular places and times which limit the application of the idea to a single individual, while abstract general ideas leave out the ideas of particular times and places in order to allow the idea to apply to other similar qualities or things. There has been considerable philosophical and scholarly debate about the nature of the process of abstraction and Locke’s account of it. Berkeley argued that the process as Locke conceives it is incoherent. In part this is because Berkeley is an imagist—that is he believes that all ideas are images. If one is an imagist it becomes impossible to imagine what idea could include both the ideas of a right and equilateral triangle. Michael Ayers has recently argued that Locke too was an imagist. This would make Berkeley’s criticism of Locke very much to the point. Ayers’ claim, however, has been disputed (see, for example, Soles 1999). The process of abstraction is of considerable importance to human knowledge. Locke thinks most words we use are general (III.1.1, N: 409). Clearly, it is only general or sortal ideas that can serve in a classificatory scheme.

In his discussion of names of substances and in the contrast between names of substances and names of modes, a number of interesting features of Locke’s views about language and knowledge emerge. Physical substances are atoms and things made up of atoms. But we have no experience of the atomic structure of horses and tables. We know horses and tables mainly by secondary qualities such as color, taste and smell and so on and primary qualities such as shape, motion and extension. So, since the real essence (the atomic constitution) of a horse is unknown to us, our word ‘horse’ cannot get its meaning from that real essence. What the general word signifies is the complex of ideas we have decided are parts of the idea of that sort of thing. These ideas we get from experience. Locke calls such a general idea that picks out a sort, the nominal essence of that sort.

One of the central issues in Book III has to do with classification. On what basis do we divide things into kinds and organize those kinds into a system of species and genera? In the Aristotelian and Scholastic tradition that Locke rejects, necessary properties are those that an individual must have in order to exist and continue to exist. These contrast with accidental properties. Accidental properties are those that an individual can gain and lose and yet continue in existence. If a set of necessary properties is shared by a number of individuals, that set of properties constitutes the essence of a natural kind. The borders between kinds are supposed to be sharp and determinate. The aim of Aristotelian science is to discover the essences of natural kinds. Kinds can then be organized hierarchically into a classificatory system of species and genera. This classification of the world by natural kinds will be unique and privileged because it alone corresponds to the structure of the world. This doctrine of essences and kinds is often called Aristotelian essentialism. Locke rejects a variety of aspects of this doctrine. He rejects the notion that an individual has an essence apart from being treated as belonging to a kind. He also rejects the claim that there is a single classification of things in nature that the natural philosopher should seek to discover. He holds that there are many possible ways to classify the world each of which might be particularly useful depending on one’s purposes.

Locke’s pragmatic account of language and the distinction between nominal and real essences constitute an anti-essentialist alternative to this Aristotelian essentialism and its correlative account of the classification of natural kinds. He claims that there are no fixed boundaries in nature to be discovered—that is there are no clear demarcation points between species. There are always borderline cases. There is debate over whether Locke’s view is that this lack of fixed boundaries is true on both the level of appearances and nominal essences, and atomic constitutions and real essences, or on the level of nominal essences alone. The first view is that Locke holds that there are no Aristotelian natural kinds on either the level of appearance or atomic reality. The second view holds that Locke thinks there are Aristotelian natural kinds on the atomic level, it is simply that we cannot get at them or know what they are. On either of these interpretations, the real essence cannot provide the meaning to names of substances. A.O. Lovejoy in the Great Chain of Being , and David Wiggins are proponents of the second interpretation while Michael Ayers and William Uzgalis argue for the first (Uzgalis 1988; Ayers 1991: II. 70).

By contrast, the ideas that we use to make up our nominal essences come to us from experience. Locke claims that the mind is active in making our ideas of sorts and that there are so many properties to choose among that it is possible for different people to make quite different ideas of the essence of a certain substance. This has given some commentators the impression that the making of sorts is utterly arbitrary and conventional for Locke and that there is no basis for criticizing a particular nominal essence. Sometimes Locke says things that might suggest this. But this impression should be resisted. Peter Anstey has characterized Locke’s conventionalism about classificatory terms as both constrained and convergent (Anstey 2011: 209, 212). Locke claims that while the making of nominal essences is the work of the understanding, that work is constrained both by usage (where words stand for ideas that are already in use) and by the fact that substance words are supposed to copy the properties of the substances they refer to. Locke says that our ideas of kinds of substances have as their archetype the complex of properties that produce the appearances we use to make our nominal essences and which cause the unity of the complex of ideas that appear to us regularly conjoined. The very notion of an archetype implies constraints on what properties (and hence what ideas) can go together. If there were no such constraints there could be no archetype. (For further discussion of the nominal-real essence distinction see the entry Locke on Real Essences) .

Let us begin with the usage of words. It is important in a community of language users that words be used with the same meaning. If this condition is met it facilitates the chief end of language which is communication. If one fails to use words with the meaning that most people attach to them, one will fail to communicate effectively with others. Thus one would defeat the main purpose of language. It should also be noted that traditions of usage for Locke can be modified. Otherwise we would not be able to improve our knowledge and understanding by getting more clear and determinate ideas.

In the making of the names of substances, there is a period of discovery as the abstract general idea is put together (e.g. the discovery of violets or gold) and then the naming of that idea and then its introduction into language. Language itself is viewed as an instrument for carrying out the mainly prosaic purposes and practices of everyday life. Ordinary people are the chief makers of language.

Vulgar Notions suit vulgar Discourses; and both though confused enough, yet serve pretty well for the Market and the Wake. Merchants and Lovers, Cooks and Taylors, have Words wherewith to dispatch their ordinary affairs; and so, I think, might Philosophers and Disputants too, if they had a mind to understand and to be clearly understood. (III.11.10, N: 514)

These ordinary people use a few apparent qualities, mainly ideas of secondary qualities to make ideas and words that will serve their purposes.

Natural philosophers (i.e. scientists) come along later to try to determine if the connections between properties which the ordinary folk have put together in a particular idea in fact holds in nature. Scientists are seeking to find the necessary connections between properties. Still, even scientists, in Locke’s view, are restricted to using observable (and mainly secondary) qualities to categorize things in nature. Sometimes, the scientists may find that the ordinary folk had erred, as when they called whales ‘fish’. A whale is not a fish, as it turns out, but a mammal. There is a characteristic group of qualities that fish have that whales do not have. There is a characteristic group of qualities that mammals have that whales also have. To classify a whale as a fish, therefore, is a mistake. Similarly, we might make an idea of gold that only included being a soft metal and gold color. If so, we would be unable to distinguish between gold and fool’s gold. Thus, since it is the mind that makes complex ideas (they are ‘the workmanship of the understanding’), one is free to put together any combination of ideas one wishes and call it what one will. But the product of such work is open to criticism, either on the grounds that it does not conform to already current usage or that it inadequately represents the archetypes that it is supposed to copy in the world. We engage in such criticism in order to improve human understanding of the material world and thus the human condition. This is the convergent character of Locke’s conventionalism. In becoming more accurate, the nominal essence converges on the real essence.

However, we should not forget the master-builders that Locke mentions at the beginning of the Essay . Stephen Gaukroger (2010) claims that Locke’s great achievement was to provide a philosophical justification for the kind of experimental philosophy that Boyle’s work on the air pump, and his and Newton’s work on colors, as well as Sydenham’s observational medicine. All of these had been attacked for not providing explanations in terms of matter theory. Thus, Locke is justifying the autonomy of experimental philosophy. Such experimental explanations depend solely on the relation between phenomena, even when there is some micro-corpuscular basis for the phenomena being explained. According to Gaukroger, this is Locke’s contribution to the collapse of mechanism. For the details of the problem and its solution, see Chapters 4 and 5 of Gaukroger (2010).

The distinction between modes and substances is surely one of the most important in Locke’s philosophy. In contrast with substances, modes are dependent existences—they can be thought of as the ordering of substances. These are technical terms for Locke, so we should see how they are defined. Locke writes:

First, Modes I call such complex Ideas , which however compounded, contain not in themselves the supposition of subsisting by themselves; such are the ideas signified by the Words Triangle, Gratitude, Murther, etc . (II.12.4, N: 165)

Locke goes on to distinguish between simple and mixed modes. He writes:

Of these Modes , there are two sorts, which deserve distinct consideration. First, there are some that are only variations, or different combinations of the same simple Idea , without the mixture of any other, as a dozen or score; which are nothing but the ideas of so many distinct unities being added together, and these I call simple Modes , as being contained within the bounds of one simple Idea . Secondly, There are others, compounded of Ideas of several kinds, put together to make one complex one; v.g. Beauty , consisting of a certain combination of Colour and Figure, causing Delight to the Beholder; Theft , which being the concealed change of the Possession of any thing, without the consent of the Proprietor, contains, as is visible, a combination of several Ideas of several kinds; and these I call Mixed Modes . (II.12.5, N: 165)

When we make ideas of modes, the mind is again active, but the archetype is in our mind. The question becomes whether things in the world fit our ideas, and not whether our ideas correspond to the nature of things in the world. Our ideas are adequate. Thus we define ‘bachelor’ as an unmarried, adult, male human being. If we find that someone does not fit this definition, this does not reflect badly on our definition, it simply means that that individual does not belong to the class of bachelors. Modes give us the ideas of mathematics, of morality, of religion and politics and indeed of human conventions in general. Since these modal ideas are not only made by us but serve as standards that things in the world either fit or do not fit and thus belong or do not belong to that sort, ideas of modes are clear and distinct, adequate and complete. Thus in modes, we get the real and nominal essences combined. One can give precise definitions of mathematical terms (that is, give necessary and sufficient conditions), and one can give deductive demonstrations of mathematical truths. Locke sometimes says that morality too is capable of deductive demonstration. Though pressed by his friend William Molyneux to produce such a demonstrative morality, Locke never did so. The entry Locke’s moral philosophy provides an excellent discussion of Locke’s views on morality and issues related to them for which there is no room in this general account. The terms of political discourse also have some of the same modal features for Locke. When Locke defines the states of nature, slavery, and war in the Second Treatise of Government , for example, we are presumably getting precise modal definitions from which one can deduce consequences. It is possible, however, that with politics we are getting a study that requires both experience as well as the deductive modal aspect.

In the fourth book of An Essay Concerning Human Understanding Locke tells us what knowledge is and what humans can know and what they cannot (not simply what they do and do not happen to know). Locke defines knowledge as “the perception of the connexion and agreement or disagreement and repugnancy of any of our Ideas” (IV.1.1, N: 525). This definition of knowledge contrasts with the Cartesian definition of knowledge as any ideas that are clear and distinct. Locke’s account of knowledge allows him to say that we can know substances in spite of the fact that our ideas of them always include the obscure and relative idea of substance in general. Still, Locke’s definition of knowledge raises in this domain a problem analogous to those we have seen with perception and language. If knowledge is the “perception of … the agreement or disagreement … of any of our Ideas”—are we not trapped in the circle of our own ideas? What about knowing the real existence of things? Locke is plainly aware of this problem, and very likely holds that the implausibility of skeptical hypotheses, such as Descartes’ Dream hypothesis (he doesn’t even bother to mention Descartes’ malin genie or Evil Demon hypothesis), along with the causal connections between qualities and ideas in his own system is enough to solve the problem. It is also worth noting that there are significant differences between Locke’s brand of empiricism and that of Berkeley that would make it easier for Locke to solve the veil of perception problem than Berkeley. Locke, for example, makes transdictive inferences about atoms where Berkeley is unwilling to allow that such inferences are legitimate. This implies that Locke has a semantics that allows him to talk about the unexperienced causes of experience (such as atoms) where Berkeley cannot. (See Mackie’s perceptive discussion of the veil of perception problem, in Problems from Locke , 1976: 51 through 67.)

What then can we know and with what degree of certainty? We can know that God exists with the second highest degree of assurance, that of demonstration. We also know that we exist with the highest degree of certainty. The truths of morality and mathematics we can know with certainty as well, because these are modal ideas whose adequacy is guaranteed by the fact that we make such ideas as ideal models which other things must fit, rather than trying to copy some external archetype which we can only grasp inadequately. On the other hand, our efforts to grasp the nature of external objects are limited largely to the connection between their apparent qualities. The real essence of elephants and gold is hidden from us: though in general we suppose them to be some distinct combination of atoms which cause the grouping of apparent qualities which leads us to see elephants and violets, gold and lead as distinct kinds. Our knowledge of material things is probabilistic and thus opinion rather than knowledge. Thus our “knowledge” of external objects is inferior to our knowledge of mathematics and morality, of ourselves, and of God. We do have sensitive knowledge of external objects, which is limited to things we are presently experiencing. While Locke holds that we only have knowledge of a limited number of things, he thinks we can judge the truth or falsity of many propositions in addition to those we can legitimately claim to know. This brings us to a discussion of probability.

Knowledge involves the seeing of the agreement or disagreement of our ideas. What then is probability and how does it relate to knowledge? Locke writes:

The Understanding Faculties being given to Man, not barely for Speculation, but also for the Conduct of his Life, Man would be at a great loss, if he had nothing to direct him, but what has the Certainty of true Knowledge … Therefore, as God has set some Things in broad day-light; as he has given us some certain Knowledge…So in the greater part of our Concernment, he has afforded us only the twilight, as I may say so, of Probability, suitable, I presume, to that State of Mediocrity and Probationership, he has been pleased to place us in here, wherein to check our over-confidence and presumption, we might by every day’s Experience be made sensible of our short sightedness and liableness to Error… (IV.14.1–2, N: 652)

So, apart from the few important things that we can know for certain, e.g. the existence of ourselves and God, the nature of mathematics and morality broadly construed, for the most part we must lead our lives without knowledge. What then is probability? Locke writes:

As Demonstration is the shewing of the agreement or disagreement of two Ideas, by the intervention of one or more Proofs, which have a constant, immutable, and visible connexion one with another: so Probability is nothing but the appearance of such an Agreement or Disagreement, by the intervention of Proofs, whose connection is not constant and immutable, or at least is not perceived to be so, but is or appears, for the most part to be so, and is enough to induce the Mind to judge the Proposition to be true, or false, rather than the contrary. (IV.15.1, N: 654)

Probable reasoning, on this account, is an argument, similar in certain ways to the demonstrative reasoning that produces knowledge but different also in certain crucial respects. It is an argument that provides evidence that leads the mind to judge a proposition true or false but without a guarantee that the judgment is correct. This kind of probable judgment comes in degrees, ranging from near demonstrations and certainty to unlikeliness and improbability in the vicinity of impossibility. It is correlated with degrees of assent ranging from full assurance down to conjecture, doubt and distrust.

The new science of mathematical probability had come into being on the continent just around the time that Locke was writing the Essay . His account of probability, however, shows little or no awareness of mathematical probability. Rather it reflects an older tradition that treated testimony as probable reasoning. Given that Locke’s aim, above all, is to discuss what degree of assent we should give to various religious propositions, the older conception of probability very likely serves his purposes best. Thus, when Locke comes to describe the grounds for probability he cites the conformity of the proposition to our knowledge, observation and experience, and the testimony of others who are reporting their observation and experience. Concerning the latter we must consider the number of witnesses, their integrity, their skill in observation, counter testimony and so on. In judging rationally how much to assent to a probable proposition, these are the relevant considerations that the mind should review. We should, Locke also suggests, be tolerant of differing opinions as we have more reason to retain the opinions we have than to give them up to strangers or adversaries who may well have some interest in our doing so.

Locke distinguishes two sorts of probable propositions. The first of these have to do with particular existences or matters of fact, and the second that are beyond the testimony of the senses. Matters of fact are open to observation and experience, and so all of the tests noted above for determining rational assent to propositions about them are available to us. Things are quite otherwise with matters that are beyond the testimony of the senses. These include the knowledge of finite immaterial spirits such as angels or things such as atoms that are too small to be sensed, or the plants, animals or inhabitants of other planets that are beyond our range of sensation because of their distance from us. Concerning this latter category, Locke says we must depend on analogy as the only help for our reasoning. He writes:

Thus the observing that the bare rubbing of two bodies violently one upon the other, produce heat, and very often fire it self, we have reason to think, that what we call Heat and Fire consist of the violent agitation of the imperceptible minute parts of the burning matter…. (IV.16.12, N: 665–6)

We reason about angels by considering the Great Chain of Being; figuring that while we have no experience of angels, the ranks of species above us is likely as numerous as that below of which we do have experience. This reasoning is, however, only probable.

The relative merits of the senses, reason and faith for attaining truth and the guidance of life were a significant issue during this period. As noted above James Tyrrell recalled that the original impetus for the writing of An Essay Concerning Human Understanding was a discussion about the principles of morality and revealed religion. In Book IV Chapters 17, 18, and 19 Locke deals with the nature of reason, the relation of reason to faith and the nature of enthusiasm. Locke remarks that all sects make use of reason as far as they can. It is only when this fails them that they have recourse to faith and claim that what is revealed is above reason. But he adds:

And I do not see how they can argue with anyone or even convince a gainsayer who uses the same plea, without setting down strict boundaries between faith and reason. (IV.18.2, N: 689)

Locke then defines reason as

the discovery of the certainty or probability of such propositions or truths, which the mind arrives at by deduction made from such ideas, as it has got by the use of its natural faculties; viz, by the use of sensation or reflection. (IV.18.2, N: 689)

Faith, on the other hand, is assent to any proposition “…upon the credit of the proposer, as coming from God, in some extraordinary way of communication”. That is we have faith in what is disclosed by revelation and which cannot be discovered by reason. Locke also distinguishes between the original revelation by God to some person, and traditional revelation which is the original revelation “…delivered over to others in Words, and the ordinary ways of our conveying our Conceptions one to another” (IV.18.3, N: 690).

Locke makes the point that some things could be discovered both by reason and by revelation—God could reveal the propositions of Euclid’s geometry, or they could be discovered by reason. In such cases there would be little use for faith. Traditional revelation can never produce as much certainty as the contemplation of the agreement or disagreement of our own ideas. Similarly revelations about matters of fact do not produce as much certainty as having the experience oneself. Revelation, then, cannot contradict what we know to be true. If it could, it would undermine the trustworthiness of all of our faculties. This would be a disastrous result. Where revelation comes into its own is where reason cannot reach. Where we have few or no ideas for reason to contradict or confirm, these are the proper matters for faith.

…that Part of the Angels rebelled against GOD, and thereby lost their first happy state: and that the dead shall rise, and live again: These and the like, being Beyond the Discovery of Reason, are purely matters of Faith; with which Reason has nothing to do. (IV.18.8, N: 694)

Still, reason does have a crucial role to play in respect to revelation. Locke writes:

Because the Mind, not being certain of the Truth of that it evidently does not know, but only yielding to the Probability that appears to it, is bound to give up its assent to such Testimony, which, it is satisfied, comes from one who cannot err, and will not deceive. But yet, it still belongs to Reason, to judge of the truth of its being a Revelation, and of the significance of the Words, wherein it is delivered. (IV.18.8, N: 694)

So, in respect to the crucial question of how we are to know whether a revelation is genuine, we are supposed to use reason and the canons of probability to judge. Locke claims that if the boundaries between faith and reason are not clearly marked, then there will be no place for reason in religion and one then gets all the “extravagant Opinions and Ceremonies, that are to be found in the religions of the world…” (IV.18.11, N: 696).

Should one accept revelation without using reason to judge whether it is genuine revelation or not, one gets what Locke calls a third principle of assent besides reason and revelation, namely enthusiasm. Enthusiasm is a vain or unfounded confidence in divine favor or communication. It implies that there is no need to use reason to judge whether such favor or communication is genuine or not. Clearly when such communications are not genuine they are “the ungrounded Fancies of a Man’s own Brain” (IV.19.2, N: 698). This kind of enthusiasm was characteristic of Protestant extremists going back to the era of the civil war. Locke was not alone in rejecting enthusiasm, but he rejects it in the strongest terms. Enthusiasm violates the fundamental principle by which the understanding operates—that assent be proportioned to the evidence. To abandon that fundamental principle would be catastrophic. This is a point that Locke also makes in The Conduct of the Understanding and The Reasonableness of Christianity . Locke wants each of us to use our understanding to search after truth. Of enthusiasts, those who would abandon reason and claim to know on the basis of faith alone, Locke writes:

…he that takes away Reason to make way for Revelation, puts out the Light of both, and does much what the same, as if he would perswade a Man to put out his eyes, the better to receive the remote Light of an invisible Star by a Telescope. (IV.19.4, N: 698)

Rather than engage in the tedious labor required to reason correctly to judge of the genuineness of their revelation, enthusiasts persuade themselves that they are possessed of immediate revelation. This leads to “odd Opinions and extravagant actions” that are characteristic of enthusiasm and which should warn that this is a wrong principle. Thus, Locke strongly rejects any attempt to make inward persuasion not judged by reason a legitimate principle.

We turn now to a consideration of Locke’s educational works.

Locke’s Some Thoughts Concerning Education and his Conduct of the Understanding form a nice bridge between An Essay Concerning Human Understanding and his political works. Ruth Grant and Nathan Tarcov write in the introduction to their edition of these works:

The idea of liberty, so crucial to all of Locke’s writings on politics and education, is traced in the Essay to reflection on the power of the mind over one’s own actions, especially the power to suspend actions in the pursuit of the satisfaction of one’s own desires until after a full consideration of their objects (II.21.47, N: 51–52). The Essay thus shows how the independence of mind pursued in the Conduct is possible. (G&T 1996: xvi)

Some Thoughts Concerning Education was first published in 1693. This book collected together advice that Locke had been giving his friend Edward Clarke about the education of Clarke’s son (and also his daughters) since 1684. In preparing the revision for the fourth edition of An Essay Concerning Human Understanding Locke began writing a chapter called “The Conduct of the Understanding”. This became quite long and was never added to the Essay or even finished. It was left to Locke’s literary executors to decide what to do with it. The Conduct was published by Peter King in his posthumous edition of some of Locke’s works in 1706. As Locke was composing these works, some of the material from the Conduct eventually made its way into the Thoughts . Grant and Tarcov write that the Thoughts and the Conduct “complement each other well: the Thoughts focuses on the education of children by their parents, whereas the Conduct addresses the self-education of adults” (G&T 1996: vii). Though they also note tensions between the two that illustrate paradoxes in liberal society. The Thoughts is addressed to the education of the sons and daughters of the English gentry in the late seventeenth century. It is in some ways thus significantly more limited to its time and place than the Conduct . Yet, its insistence on the inculcating such virtues as

justice as respect for the rights of others, civility, liberality, humanity, self-denial, industry, thrift, courage, truthfulness, and a willingness to question prejudice, authority and the biases of one’s own self-interest

very likely represents the qualities needed for citizens in a liberal society (G&T 1996: xiii).

Locke’s Thoughts represents the culmination of a century of what has been called “the discovery of the child”. In the Middle Ages the child was regarded as

only a simple plaything, as a simple animal, or a miniature adult who dressed, played and was supposed to act like his elders…Their ages were unimportant and therefore seldom known. Their education was undifferentiated, either by age, ability or intended occupation. (Axtell 1968: 63–4)

Locke treated children as human beings in whom the gradual development of rationality needed to be fostered by parents. Locke urged parents to spend time with their children and tailor their education to their character and idiosyncrasies, to develop both a sound body and character, and to make play the chief strategy for learning rather than rote learning or punishment. Thus, he urged learning languages by learning to converse in them before learning rules of grammar. Locke also suggests that the child learn at least one manual trade.

In advocating a kind of education that made people who think for themselves, Locke was preparing people to effectively make decisions in their own lives—to engage in individual self-government—and to participate in the government of their country. The Conduct reveals the connections Locke sees between reason, freedom and morality. Reason is required for good self-government because reason insofar as it is free from partiality, intolerance and passion and able to question authority leads to fair judgment and action. We thus have a responsibility to cultivate reason in order to avoid the moral failings of passion, partiality and so forth (G&T 1996: xii). This is, in Tarcov’s phrase, Locke’s education for liberty.

We turn now to Locke’s political writings. (See the entry on Locke’s political philosophy , which focuses on five topics (the state of nature, natural law, property, consent and toleration) and goes into these topics in more depth than is possible in a general account and provides much useful information on the debates about them.)

4. The Two Treatises Of Government

Lord Shaftsbury had been dismissed from his post as Lord Chancellor in 1673 and had become one of the leaders of the opposition party, the Country Party. In 1679 the chief issue was the attempt by the Country Party leaders to exclude James, Duke of York from succeeding his brother Charles II to the throne. They wanted to do this because James was a Catholic, and England by this time was a firmly Protestant country. They had acquired a majority in the House of Commons through serious grass roots election campaigns, and passed an exclusion bill, but given the King’s unwillingness to see his brother excluded from the throne, the bill failed in the House of Lords. They tried a couple of more times without success. Having failed by parliamentary means, some of the Country Party leaders started plotting armed rebellion.

The Two Treatises of Government were published in 1689, long after the rebellion plotted by the Country party leaders had failed to materialize and after Shaftsbury had fled the country for Holland and died. The introduction of the Two Treatises was written after the Glorious Revolution of 1688, and gave the impression that the book was written to justify the Glorious Revolution. We now know that the Two Treatises of Government were written during the Exclusion crisis in 1681 and may have been intended in part to justify the general armed rising which the Country Party leaders were planning.

There were serious obstacles to a rebellion to force James’ exclusion from the throne. The English Anglican gentry needed to support such an action. But the Anglican church from childhood on taught that: “…men’s political duties were exhaustively determined by their terrestrial superiors, that under grave conscientious scruples they might rightly decline to carry out those decrees of authority which were in direct breach of divine law, they could under no circumstances have a right to resist such authority”. (Dunn, 1968, 48) Since by 1679 it was abundantly clear that the King opposed excluding his brother from the throne, to favor exclusion implied “explicit and self-conscious resistance to the sovereign”. Passive resistance would simply not do. On the other hand, the royal policy “outraged their deepest religious prejudices and stimulated their most obscure emotional anxieties.” So, the gentry were deeply conflicted and neither of the choices available to them looked very palatable. John Dunn goes on to remark: “To exert influence upon their choice it was above all necessary to present a more coherent ordering of their values, to show that the political tradition within which the dissenters saw their conduct was not necessarily empirically absurd or socially subversive. The gentry had to be persuaded that there could be reason for rebellion which could make it neither blasphemous or suicidal.” (Dunn, 1968, 49) To achieve this goal Locke picked the most relevant and extreme of the supporters of the divine right of Kings to attack. Sir Robert Filmer (c 1588–1653), a man of the generation of Charles I and the English Civil War, who had defended the crown in various works. His most famous work, however, Patriarcha , was published posthumously in 1680 and represented the most complete and coherent exposition of the view Locke wished to deny. Filmer held that men were born into helpless servitude to an authoritarian family, a social hierarchy and a sovereign whose only constraint was his relationship with God. Under these circumstances, anything other than passive obedience would be “vicious, blasphemous and intellectually absurd.” So, Locke needed to refute Filmer and in Dunn’s words: “rescue the contractarian account of political obligation from the criticism of impiety and absurdity. Only in this way could he restore to the Anglican gentry a coherent basis for moral autonomy or a practical initiative in the field of politics.” (Dunn, 1968, 50)

The First Treatise of Government is a polemical work aimed at refuting the theological basis for the patriarchal version of the Divine Right of Kings doctrine put forth by Sir Robert Filmer. Locke singles out Filmer’s contention that men are not “naturally free” as the key issue, for that is the “ground” or premise on which Filmer erects his argument for the claim that all “legitimate” government is “absolute monarchy”—kings being descended from the first man, Adam, and their subjects being naturally slaves. Early in the First Treatise Locke denies that either scripture or reason supports Filmer’s premise or arguments. In what follows in the First Treatise , Locke minutely examines key Biblical passages.

While The Second Treatise of Government provides Locke’s positive theory of government, it also continues his argument against Sir Robert Filmer’s claims that monarchs legitimately hold absolute power over their subjects. Locke holds that Filmer’s view is sufficiently incoherent to lead to governments being established by force and violence. Thus, Locke claims he must provide an alternative account of the origin of government “lest men fall into the dangerous belief that all government in the world is merely the product of force and violence” ( Treatises II,1,4). Locke’s account involves several devices which were common in seventeenth and eighteenth century political philosophy—natural rights theory and the social contract. Natural rights are those rights which we are supposed to have as human beings before ever government comes into being. We might suppose, that like other animals, we have a natural right to struggle for our survival. Locke will argue that we have a right to the means to survive. When Locke comes to explain how government comes into being, he uses the idea that people agree that their condition in the state of nature is unsatisfactory, and so agree to transfer some of their rights to a central government, while retaining others. This is the theory of the social contract. There are many versions of natural rights theory and the social contract in seventeenth and eighteenth century European political philosophy, some conservative and some radical. Locke’s version belongs on the radical side of the spectrum. These radical natural right theories influenced the ideologies of the American and French revolutions.

Locke’s strategy for refuting Filmer’s claims that monarchs have absolute power over their subjects is to show that Filmer is conflating a whole variety of limited powers, all of which might be held by one man and thus give the false appearance that a king has absolute power over wives, children, servants and slaves as well as subjects of a commonwealth. When properly distinguished, however, and the limitations of each displayed, it becomes clear that monarchs have no legitimate absolute power over their subjects.

An important part of Locke’s project in the Second Treatise is to figure out what the role of legitimate government is, thus allowing him to distinguish the nature of illegitimate government. Once this is done, the basis for legitimate revolution becomes clear. Figuring out what the proper or legitimate role of civil government is would be a difficult task indeed if one were to examine the vast complexity of existing governments. How should one proceed? One strategy is to consider what life is like in the absence of civil government. Presumably this is a simpler state, one which may be easier to understand. Then one might see what role civil government ought to play. This is the strategy which Locke pursues, following Hobbes and others. So, in the first chapter of the Second Treatise Locke defines political power.

Political power , then, I take to be a right of making laws with penalties of death, and consequently all less penalties, for the regulating and preserving of property, and of employing the force of the community, in the execution of such laws, and in the defence of the common-wealth from foreign injury; and all this only for the public good. ( Treatises, II, 1,3)

In the second chapter of The Second Treatise Locke describes the state in which there is no government with real political power. This is the state of nature. It is sometimes assumed that the state of nature is a state in which there is no government at all. This is only partially true. It is possible to have in the state of nature either no government, illegitimate government, or legitimate government with less than full political power. (See the section on the state of nature in the entry on Locke’s political philosophy.)

If we consider the state of nature before there was government, it is a state of political equality in which there is no natural superior or inferior. From this equality flows the obligation to mutual love and the duties that people owe one another, and the great maxims of justice and charity. Was there ever such a state? There has been considerable debate about this. Still, it is plain that both Hobbes and Locke would answer this question affirmatively. Whenever people have not agreed to establish a common political authority, they remain in the state of nature. It’s like saying that people are in the state of being naturally single until they are married. Locke clearly thinks one can find the state of nature in his time at least in the “inland, vacant places of America” ( Second Treatise V. 36) and in the relations between different peoples. Perhaps the historical development of states also went though the stages of a state of nature. An alternative possibility is that the state of nature is not a real historical state, but rather a theoretical construct, intended to help determine the proper function of government. If one rejects the historicity of states of nature, one may still find them a useful analytical device. For Locke, it is very likely both.

According to Locke, God created man and we are, in effect, God’s property. The chief end set us by our creator as a species and as individuals is survival. A wise and omnipotent God, having made people and sent them into this world:

…by his order and about his business, they are his property whose workmanship they are, made to last during his, not one another’s pleasure: and being furnished with like faculties, sharing all in one community of nature, there cannot be supposed any subordination among us, that may authorize us to destroy one another, as if we were made for one another’s uses, as the inferior ranks of creatures are for our’s. ( Treatises II,2,6)

It follows immediately that “he has no liberty to destroy himself, or so much as any creature in his possession, yet when some nobler use than its bare possession calls for it” ( Treatises II.2.6). So, murder and suicide violate the divine purpose.

If one takes survival as the end, then we may ask what are the means necessary to that end. On Locke’s account, these turn out to be life, liberty, health and property. Since the end is set by God, on Locke’s view we have a right to the means to that end. So we have rights to life, liberty, health and property. These are natural rights, that is they are rights that we have in a state of nature before the introduction of civil government, and all people have these rights equally.

There is also a law of nature. It is the Golden Rule, interpreted in terms of natural rights. Thus Locke writes:

The state of nature has a law of nature to govern it, which obliges everyone: and reason which is that law, teaches all mankind who will but consult it, that being all equal and independent, no one ought to harm another in his life, health, liberty or possessions…. ( Treatises II.2.6)

Locke tells us that the law of nature is revealed by reason. Locke makes the point about the law that it commands what is best for us. If it did not, he says, the law would vanish for it would not be obeyed. It is in this sense that Locke means that reason reveals the law. If you reflect on what is best for yourself and others, given the goal of survival and our natural equality, you will come to this conclusion. (See the section on the law of nature in the entry on Locke’s Political Philosophy.)

Locke does not intend his account of the state of nature as a sort of utopia. Rather it serves as an analytical device that explains why it becomes necessary to introduce civil government and what the legitimate function of civil government is. Thus, as Locke conceives it, there are problems with life in the state of nature. The law of nature, like civil laws can be violated. There are no police, prosecutors or judges in the state of nature as these are all representatives of a government with full political power. The victims, then, must enforce the law of nature in the state of nature. In addition to our other rights in the state of nature, we have the rights to enforce the law and to judge on our own behalf. We may, Locke tells us, help one another. We may intervene in cases where our own interests are not directly under threat to help enforce the law of nature. This right eventually serves as the justification for legitimate rebellion. Still, in the state of nature, the person who is most likely to enforce the law under these circumstances is the person who has been wronged. The basic principle of justice is that the punishment should be proportionate to the crime. But when the victims are judging the seriousness of the crime, they are more likely to judge it of greater severity than might an impartial judge. As a result, there will be regular miscarriages of justice. This is perhaps the most important problem with the state of nature.

In chapters 3 and 4, Locke defines the states of war and slavery. The state of war is a state in which someone has a sedate and settled intention of violating someone’s right to life (and thus all their other rights). Such a person puts themselves into a state of war with the person whose life they intend to take. In such a war the person who intends to violate someone’s right to life is an unjust aggressor. This is not the normal relationship between people enjoined by the law of nature in the state of nature. Locke is distancing himself from Hobbes who had made the state of nature and the state of war equivalent terms. For Locke, the state of nature is ordinarily one in which we follow the Golden Rule interpreted in terms of natural rights, and thus love our fellow human creatures. The state of war only comes about when someone proposes to violate someone else’s rights. Thus, on Locke’s theory of war, there will always be an innocent victim on one side and an unjust aggressor on the other.

Slavery is the state of being in the absolute or arbitrary power of another. On Locke’s definition of slavery, there is only one rather remarkable way to become a legitimate slave. In order to do so, one must be an unjust aggressor defeated in war. The just victor then has the option to either kill the aggressor or enslave them. Locke tells us that the state of slavery is the continuation of the state of war between a lawful conqueror and a captive, in which the conqueror delays taking the life of the captive, and instead makes use of him. This is a continued war because if conqueror and captive make some compact for obedience on the one side and limited power on the other, the state of slavery ceases and becomes a relation between a master and a servant in which the master only has limited power over his servant. The reason that slavery ceases with the compact is that “no man, can, by agreement pass over to another that which he hath not in himself, a power over his own life” ( Treatises II.4.24). Legitimate slavery is an important concept in Locke’s political philosophy largely because it tells us what the legitimate extent of despotic power is and defines and illuminates by contrast the nature of illegitimate slavery. Illegitimate slavery is that state in which someone possesses absolute or despotic power over someone else without just cause. Locke holds that it is this illegitimate state of slavery which absolute monarchs wish to impose upon their subjects. It is very likely for this reason that legitimate slavery is so narrowly defined. This shows that the chapter on slavery plays a crucial role in Locke’s argument against Sir Robert Filmer and thus could not have been easily dispensed with. Still, it is possible that Locke had an additional purpose or perhaps a quite different reason for writing about slavery.

There has been a steady stream of articles and books over the last sixty years arguing that given Locke’s involvement with trade and colonial government, the theory of slavery in the Second Treatise was intended to justify the institutions and practices of Afro-American slavery. If this were the case, Locke’s philosophy would not contradict his actions as an investor and colonial administrator. However, there are strong objections to this view. Had he intended to justify Afro-American slavery, Locke would have done much better with a vastly more inclusive definition of legitimate slavery than the one he gives. It is sometimes suggested that Locke’s account of “just war” is so vague that it could easily be twisted to justify the institutions and practices of Afro-American slavery. This, however, is also not the case. In the chapter “Of Conquest” Locke explicitly lists the limits of the legitimate power of conquerors. These limits on who can become a legitimate slave and what the powers of a just conqueror are ensure that this theory of conquest and slavery would condemn the institutions and practices of Afro-American slavery in the seventeenth, eighteenth, and nineteenth centuries. Nonetheless, the debate continues. One element of the debate has to do with Locke’s role in the writing of the Fundamental Constitutions of the Carolinas . David Armitage in his 2004 article “John Locke, Carolina and the Two Treatises of Government” argues that Locke was involved in a revision of the Fundamental Constitution of the Carolinas at the very time he was writing The Two Treatises of Government . The provision that “Every Freedman of the Carolinas has absolute power and authority over his negro slaves” remained in the document unchanged. In his 2016 book The Ashley Cooper Plan , Thomas Wilson gives a detailed account of Ashley Cooper’s intentions for the Carolina colony and how Cooper’s intent was thwarted by Barbadian slave owners who changed Carolina society from a society with slaves to a slave society. L. H. Roper, in his 2004 book Conceiving Carolina: Property, Planters and Plots 1662–1729 , offers a different account of what went wrong, focusing on conflicts over the trade in Indian slaves. James Farr’s article “Locke, Natural Law and New World Slavery” (2008) is one of the best statements of the position that Locke intended his theory of slavery to apply to English absolutism and not Afro-American slavery while noting that Locke’s involvement with slavery has ruined his reputation as the great champion of liberty Roger Woolhouse in his recent biography of Locke (Woolhouse 2007: 187) remarks that “Though there is no consensus on the whole question, there certainly seems to be ‘a glaring contradiction between his theories and Afro-American slavery’”.

Recently, there has been a debate over whose theory of slavery and absolutism Locke was attacking. Johan Olsthoorn and Laurens van Apeldoorn (2020) argue that Locke’s account of slavery and in particular, that no person can consensually establish absolute rule over themselves with all its consequences has little force against other classical contract theories, in particular those of Grotius and Puffendorf. Both Grotius and Puffendorf defended both absolutism and colonial slavery.

Felis Waldmann in “Slavery and Absolutism in Locke’s Two Treatises: A Response to Olsthoorn and van Apeldoorn” objects to a number of their claims finding others not relevant. Most notably, he objects to these claims: First, “Locke is working with an idiosyncratic conception of slavery and absolute rule repudiated by prominent early modern thinkers defending political absolutism.” Second: “Like Filmer, Locke maintains that absolute rulers may arbitrarily kill and maim their subjects at will, by dint of having a dominium in the latter’s lives.” Finally, he objects to the claim that: “Early modern natural lawyers, from Grotius onward, conceptualized slavery rather differently, insisting that enslaved people were not owned in the way we own things (which may be destroyed at will)” (Waldmann 7).

In brief, Waldmann’s response to the first claim is that Filmer accurately represented the Royalist position in the late 1670s and early 1680s and so Locke’s account is not a straw man. Thus, Locke is attacking Filmer’s account of slavery and not some weak and extreme version of the argument for absolutism that no one held. Waldmann suggests that the second claim magnifies this tendency of the two authors’ portrayal of Locke’s argument as not responding to the standard arguments for absolutism. Thus, Olsthoorn and van Apeldoorn attribute Filmer’s position to Locke. Waldmann concludes that the claims of Olsthoorn and van Apeldoorn that since Locke’s position on slavery was significantly different from those of Grotius and Puffendorf, it had little force against them is, in fact, the case. But he thinks this is of little importance since Locke was not arguing against them. One suggestion he considers plausible is that Locke is aiming his argument against the possibility of self-enslavement at Thomas Hobbes. Hobbes was recognized by his contemporaries as asserting both that one could by contract enslave oneself and that the king had dominium, over his subjects.

William Uzgalis, in his 2017 chapter “John Locke, Slavery and Indian Lands,” holds that Locke has two theories of slavery, one of them of legitimate slavery and the other of illegitimate slavery. Note that the authors discussed above simply don’t make this distinction. If they had, it would be plain that while Locke shares with Filmer the dominium conception of slavery that allows a master to kill or maim a slave, neither theory belongs to Filmer, and if Locke is correct about royal absolutism and given the character of the practices of the slave trade and colonial slavery, both absolutism at home and the slave trade and colonial slavery fall under the theory of illegitimate slavery. Neither Grotius, Puffendorf or Hobbes has an explicit theory of illegitimate slavery. Uzgalis also notes that Grotius and Puffendorf provided claims that Locke could have adopted had he wished to justify the slave trade and slavery in the colonies. Still, he denies them all, and with good reason. He would have substantially weakened his argument against the kind of absolutism he attributed to Filmer and the Stuarts had he done so. This suggests that he was crafting an alternative theory and not arguing against its competitors, with the exception, perhaps, of Hobbes.

Holly Brewer in her 2017 article “Slavery, Sovereignty, and ‘Inheritable Blood’, Reconsidering John Locke and the Origins of American Slavery” argues for a different approach to these questions. She presents evidence that the Stuart kings, and Charles II and his brother James, Duke of York, in particular, were not just interested in absolute government at home; they actively promoted the Royal Africa Company, the slave trade and slavery in the colonies as it provided considerable amounts of money to the royal coffers. James was the Governor (the President) of the Royal Africa Company and Admiral of the English fleet. Lord Shaftesbury, Locke’s patron, was the sub-governor, and Locke assisted him. Using the fleet, James attacked and captured Dutch forts on the coast of Africa to make bases for the Royal Africa Company and deprive the Dutch of them. The Stuarts minted guinea coins to celebrate these efforts. After becoming King, James continued as Governor of the Royal Africa Company. Thus Brewer underlines the similarities and connections between the absolutism Locke objected to at home and the slave trade and slavery in the colonies. She argues that the spread of slavery needs to be understood as an English imperial policy and not something that occurred in different times and places unconnected with one another. She also claims that while Locke was a member of King William III’s Board of Trade in the waning years of the seventeenth century, he sought to undo Stuart policies concerning slavery in the colonies.

Chapter 5 “Of Property” is one of the most famous, influential and important chapters in the Second Treatise of Government . Indeed, some of the most controversial issues about the Second Treatise come from varying interpretations of it. In this chapter Locke, in effect, describes the evolution of the state of nature to the point where it becomes expedient for those in it to found a civil government. So, it is not only an account of the nature and origin of private property but leads up to the explanation of why civil government replaces the state of nature (see the section on property in the entry on Locke’s political philosophy).

In discussing the origin of private property Locke begins by noting that God gave the earth to all men in common. Thus there is a question about how private property comes to be. Locke finds it a serious difficulty. He points out, however, that we are supposed to make use of the earth “for the best advantage of life and convenience” ( Treatises II.5.25). What then is the means to appropriate property from the common store? Locke argues that private property does not come about by universal consent. If one had to go about and ask everyone if one could eat these berries, one would starve to death before getting everyone’s agreement. Locke holds that we have property in our own person. And the labor of our body and the work of our hands properly belong to us. So, when one picks up acorns or berries, they thereby belong to the person who picked them up. There has been some controversy about what Locke means by “labor”. Daniel Russell claims that for Locke, labor is a goal-directed activity that converts materials that might meet our needs into resources that actually do (Russell 2004). This interpretation of what Locke means by “labor” connects nicely with his claim that we have a natural law obligation first to preserve ourselves and then to help in the preservation and flourishing of others.

One might think that one could then acquire as much as one wished, but this is not the case. Locke introduces at least two important qualifications on how much property can be acquired. The first qualification has to do with waste. Locke writes:

As much as anyone can make use of to any advantage of life before it spoils, so much by his labor he may fix a property in; whatever is beyond this, is more than his share, and belongs to others. ( Treatises II.5.31)

Since originally, populations were small and resources great, living within the bounds set by reason, there would be little quarrel or contention over property, for a single man could make use of only a very small part of what was available.

Note that Locke has, thus far, been talking about hunting and gathering, and the kinds of limitations which reason imposes on the kind of property that hunters and gatherers hold. In the next section he turns to agriculture and the ownership of land and the kinds of limitations there are on that kind of property. In effect, we see the evolution of the state of nature from a hunter/gatherer kind of society to that of a farming and agricultural society. Once again it is labor which imposes limitations upon how much land can be enclosed. It is only as much as one can work. But there is an additional qualification. Locke says:

Nor was this appropriation of any parcel of land , by improving it, any prejudice to any other man, since there was still enough, and as good left; and more than the as yet unprovided could use. So that, in effect, there was never the less for others because of his inclosure for himself: for he that leaves as much as another can make use of, does as good as take nothing at all. No body could consider himself injured by the drinking of another man, though he took a good draught, who had a whole river of the same water left to quench his thirst: and the case of land and water, where there is enough, is perfectly the same. ( Treatises II.5.33)

The next stage in the evolution of the state of nature involves the introduction of money. Locke remarks that:

… before the desire of having more than one needed had altered the intrinsic value of things, which depends only on their usefulness to the life of man; or had agreed, that a little piece of yellow metal, which would keep without wasting or decay, should be worth a great piece of flesh, or a whole heap of corn; though men had a right to appropriate by their labor, each one of himself, as much of the things of nature, as he could use; yet this could not be much, nor to the prejudice of others, where the same plenty was left to those who would use the same industry. ( Treatises II.5.37)

So, before the introduction of money, there was a degree of economic equality imposed on mankind both by reason and the barter system. And men were largely confined to the satisfaction of their needs and conveniences. Most of the necessities of life are relatively short lived—berries, plums, venison and so forth. One could reasonably barter one’s berries for nuts which would last not weeks but perhaps a whole year. And says Locke:

…if he would give his nuts for a piece of metal, pleased with its color, or exchange his sheep for shells, or wool for a sparkling pebble or diamond, and keep those by him all his life, he invaded not the right of others, he might heap up as much of these durable things as he pleased; the exceeding of the bounds of his property not lying in the largeness of his possessions, but the perishing of anything uselessly in it. ( Treatises II.5.146)

The introduction of money is necessary for the differential increase in property, with resulting economic inequality. Without money there would be no point in going beyond the economic equality of the earlier stage. In a money economy, different degrees of industry could give men vastly different proportions.

This partage of things in an inequality of private possessions, men have made practicable out of the bounds of society, and without compact, only by putting a value on gold and silver, and tacitly agreeing to the use of money: for in governments, the laws regulate the rights of property, and the possession of land is determined by positive constitutions. ( Treatises II.5.50)

The implication is that it is the introduction of money, which causes inequality, which in turn multiplies the causes of quarrels and contentions and increased numbers of violations of the law of nature. This leads to the decision to create a civil government. Before turning to the institution of civil government, however, we should ask what happens to the qualifications on the acquisition of property after the advent of money? One answer proposed by C. B. Macpherson in The Political Theory of Possessive Individualism is that the qualifications are completely set aside, and we now have a system for the unlimited acquisition of private property. This does not seem to be correct. It seems plain, rather, that at least the non-spoilage qualification is satisfied, because money does not spoil. The other qualifications may be rendered somewhat irrelevant by the advent of the conventions about property adopted in civil society. This leaves open the question of whether Locke approved of these changes. Macpherson, who takes Locke to be a spokesman for a proto-capitalist system, sees Locke as advocating the unlimited acquisition of wealth. James Tully, on the other side, in A Discourse of Property holds that Locke sees the new conditions, the change in values and the economic inequality which arise as a result of the advent of money, as the fall of man. Tully sees Locke as a persistent and powerful critic of self-interest. This remarkable difference in interpretation has been a significant topic for debates among scholars over the last forty years. Though the Second Treatise of Government may leave this question difficult to determine, one might consider Locke’s remark in Some Thoughts Concerning Education that

Covetousness and the desire to having in our possession and our dominion more than we have need of, being the root of all evil, should be early and carefully weeded out and the contrary quality of being ready to impart to others inculcated. (G&T 1996: 81)

Let us then turn to the institution of civil government.

Just as natural rights and natural law theory had a fluorescence in the seventeenth and eighteenth century, so did the social contract theory. Why is Locke a social contract theorist? Is it merely that this was one prevailing way of thinking about government at the time which Locke blindly adopted? The answer is that there is something about Locke’s project which pushes him strongly in the direction of the social contract. One might hold that governments were originally instituted by force, and that no agreement was involved. Were Locke to adopt this view, he would be forced to go back on many of the things which are at the heart of his project in the Second Treatise , though cases like the Norman conquest force him to admit that citizens may come to accept a government that was originally forced on them. Remember that the Second Treatise provides Locke’s positive theory of government, and that he explicitly says that he must provide an alternative to the view

that all government in the world is merely the product of force and violence, and that men live together by no other rules than that of the beasts, where the strongest carries it … . ( Treatises II, 1, 4)

So, while Locke might admit that some governments come about through force or violence, he would be destroying the most central and vital distinction, that between legitimate and illegitimate civil government, if he admitted that legitimate government can come about in this way. So, for Locke, legitimate government is instituted by the explicit consent of those governed. (See the section on consent, political obligation, and the ends of government in the entry on Locke’s political philosophy.) Those who make this agreement transfer to the government their right of executing the law of nature and judging their own case. These are the powers which they give to the central government, and this is what makes the justice system of governments a legitimate function of such governments.

Ruth Grant has persuasively argued that the establishment of government is in effect a two step process. Universal consent is necessary to form a political community. Consent to join a community once given is binding and cannot be withdrawn. This makes political communities stable. Grant writes: “Having established that the membership in a community entails the obligation to abide by the will of the community, the question remains: Who rules?” (1987: 114–115). The answer to this question is determined by majority rule. The point is that universal consent is necessary to establish a political community, majority consent to answer the question who is to rule such a community. Universal consent and majority consent are thus different in kind, not just in degree. Grant writes:

Locke’s argument for the right of the majority is the theoretical ground for the distinction between duty to society and duty to government, the distinction that permits an argument for resistance without anarchy. When the designated government dissolves, men remain obligated to society acting through majority rule. (1987: 119)

It is entirely possible for the majority to confer the rule of the community on a king and his heirs, or a group of oligarchs or on a democratic assembly. Thus, the social contract is not inextricably linked to democracy. Still, a government of any kind must perform the legitimate function of a civil government.

Locke is now in a position to explain the function of a legitimate government and distinguish it from illegitimate government. The aim of such a legitimate government is to preserve, so far as possible, the rights to life, liberty, health and property of its citizens, and to prosecute and punish those of its citizens who violate the rights of others and to pursue the public good even where this may conflict with the rights of individuals. In doing this it provides something unavailable in the state of nature, an impartial judge to determine the severity of the crime, and to set a punishment proportionate to the crime. This is one of the main reasons why civil society is an improvement on the state of nature. An illegitimate government will fail to protect the rights to life, liberty, health and property of its subjects, and in the worst cases, such an illegitimate government will claim to be able to violate the rights of its subjects, that is it will claim to have despotic power over its subjects. Since Locke is arguing against the position of Sir Robert Filmer who held that patriarchal power and political power are the same, and that in effect these amount to despotic power, Locke is at pains to distinguish these three forms of power, and to show that they are not equivalent. Thus at the beginning of chapter 15 “Of Paternal, Political and Despotic Power Considered Together” he writes:

THOUGH I have had occasion to speak of these before, yet the great mistakes of late about government, having as I suppose arisen from confounding these distinct powers one with another, it may not be amiss, to consider them together.

Chapters 6 and 7 give Locke’s account of paternal and political power respectively. Paternal power is limited. It lasts only through the minority of children, and has other limitations. Political power, derived as it is from the transfer of the power of individuals to enforce the law of nature, has with it the right to kill in the interest of preserving the rights of the citizens or otherwise supporting the public good. Legitimate despotic power, by contrast, implies the right to take the life, liberty, health and at least some of the property of any person subject to such a power.

At the end of the Second Treatise we learn about the nature of illegitimate civil governments and the conditions under which rebellion and regicide are legitimate and appropriate. As noted above, scholars now hold that the book was written during the Exclusion Crisis, and may have been written to justify a general insurrection and the assassination of the king of England and his brother. The argument for legitimate revolution follows from making the distinction between legitimate and illegitimate civil government. A legitimate civil government seeks to preserve its subjects’ life, health, liberty, and property insofar as this is compatible with the public good. Because it does this, it deserves obedience. An illegitimate civil government seeks to systematically violate the natural rights of its subjects. It seeks to make them illegitimate slaves. Because an illegitimate civil government does this, it puts itself in a state of nature and a state of war with its subjects. The magistrate or king of such a state violates the law of nature and so makes himself into a dangerous beast of prey who operates on the principle that might makes right, or that the strongest carries it. In such circumstances, rebellion is legitimate, as is the killing of such a dangerous beast of prey. Thus Locke justifies rebellion and regicide under certain circumstances. Presumably, this justification was going to be offered for the killing of the King of England and his brother had the Rye House Plot succeeded. Even if this was not Locke’s intention, it still would have served that purpose admirably.

The issue of religious toleration was of widespread interest in Europe in the seventeenth century, largely because religious intolerance with accompanying violence was so pervasive. The Reformation had split Europe into competing religious camps, and this provoked civil wars and massive religious persecutions. John Marshall, in his massive study John Locke, Toleration and Early Enlightenment Culture notes that the 1680s were the climactic decade for this kind of persecution. The Dutch Republic, where Locke spent years in exile, had been founded as a secular state which would allow religious differences. This was a reaction to the Catholic persecution of Protestants. However, once the Calvinist Church gained power, they began persecuting other sects, such as the Remonstrants, who disagreed with them. Nonetheless, The Dutch Republic remained the most tolerant country in Europe. In France, religious conflict had been temporarily quieted by the edict of Nantes. But in 1685, the year in which Locke wrote the First Letter concerning religious toleration, Louis XIV had revoked the Edict of Nantes, and the Huguenots were being persecuted. Though prohibited from doing so, some 200,000 emigrated, while probably 700,000 were forced to convert to Catholicism. People in England were keenly aware of the events taking place in France.

In England itself, religious conflict dominated the seventeenth century, contributing in important respects to the coming of the English Civil War, and the abolishing of the Anglican Church during the Protectorate. After the Restoration of Charles II, Anglicans in parliament passed laws that repressed both Catholics and Protestant sects such as Presbyterians, Baptists, Quakers and Unitarians who did not agree with the doctrines or practices of the state Church. Of these various dissenting sects, some were closer to the Anglicans, others more remote. One reason, among others, why King Charles may have found Shaftesbury useful was that they were both concerned about religious toleration. They parted when it became clear that the King was mainly interested in toleration for Catholics, and Shaftesbury for Protestant dissenters.

One widely discussed strategy for reducing religious conflict in England was called comprehension. The idea was to reduce the doctrines and practices of the Anglican church to a minimum so that most, if not all, of the dissenting sects would be included in the state church. For those which even this measure would not serve, there was to be toleration. Toleration we may define as a lack of state persecution. Neither of these strategies made much progress during the course of the Restoration.

When Locke fled to Holland after the discovery of the Rye house plot, he became involved with a group of scholars advocating religious toleration. This group included Benjamin Furly, a quaker with whom Locke lived for a while, the noted philosopher Pierre Bayle, several Dutch theologians, and many others. This group read all the arguments for religious intolerance and discussed them in book and conversation clubs. Members of the group considered toleration not only for Protestants and Protestant dissenters but Jews, Moslems, and Catholics. A recent discovery of a page of Locke’s reflections on toleration of Catholics shows that Locke considered even the pros and cons of toleration for Catholics (Walmsley and Waldmann 2019). Some members of the group also wrote tolerationist articles and books. They helped each other get jobs. Some of their members founded journals that reviewed books and articles on religious, scientific, and other topics. The group took the notion of free speech, civility, and politeness in discourse seriously. They called themselves the ‘the Republic of Letters’ or in Locke’s phrase ‘the commonwealth of learning.’

What were Locke’s religious views and where did he fit into the debates about religious toleration? This is a quite difficult question to answer. Religion and Christianity in particular, is perhaps the most important influence on the shape of Locke’s philosophy. But what kind of Christian was Locke? Locke’s family were Puritans. At Oxford, Locke avoided becoming an Anglican priest. Still, Locke himself claimed to be an Anglican until he died and Locke’s nineteenth-century biographer Fox Bourne thought that Locke was an Anglican. Others have identified him with the Latitudinarians—a movement among Anglicans to argue for a reasonable Christianity that dissenters ought to accept. Still, there are some reasons to think that Locke was neither an orthodox Anglican or a Latitudinarian. Locke got Isaac Newton to write Newton’s most powerful anti-Trinitarian tract. Locke arranged to have the work published anonymously in Holland though in the end, Newton decided not to publish (McLachlan 1941). This strongly suggests that Locke too was by this time an Arian or unitarian. (Arius, c. 250–336, asserted the primacy of the Father over the Son and thus rejected the doctrine of the Trinity and was condemned as a heretic at the Council of Nicaea in 325. Newton held that the Church had gone in the wrong direction in condemning Arius.) Given that one main theme of Locke’s Letter on Toleration is that there should be a separation between Church and State, this does not seem like the view of a man devoted to a state religion. It might appear that Locke’s writing The Reasonableness of Christianity in which he argues that the basic doctrines of Christianity are few and compatible with reason make him a Latitudinarian. Yet Richard Ashcraft has argued that comprehension for the Anglicans meant conforming to the existing practices of the Anglican Church; that is, the abandonment of religious dissent. Ashcraft also suggests that Latitudinarians were thus not a moderate middle ground between contending extremes but part of one of the extremes—“the acceptable face of the persecution of religious dissent” (Ashcraft 1992: 155). Ashcraft holds that while the Latitudinarians may have represented the “rational theology” of the Anglican church, there was a competing dissenting “rational theology”. Thus, while it is true that Locke had Latitudinarian friends, given Ashcraft’s distinction between Anglican and dissenting “rational theologies”, it is entirely possible that The Reasonableness of Christianity is a work of dissenting “rational theology”.

Locke had been thinking, talking and writing about religious toleration since 1659. His views evolved. In the early 1660s he very likely was an orthodox Anglican. He and Shaftesbury had instituted religious toleration in the Fundamental Constitutions of the Carolinas (1669). He wrote the Epistola de Tolerantia in Latin in 1685 while in exile in Holland. He very likely was seeing Protestant refugees pouring over the borders from France where Louis XIV had just revoked the Edict of Nantes. Holland itself was a Calvinist theocracy with significant problems with religious toleration. But Locke’s Letter does not confine itself to the issues of the time. Locke gives a principled account of religious toleration, though this is mixed in with arguments which apply only to Christians, and perhaps in some cases only to Protestants. He excluded both Catholics and atheists from religious toleration. In the case of Catholics it was because he regarded them as agents of a foreign power. Because they do not believe in God, atheists, on Locke’s account: “Promises, covenants and oaths, which are the bonds of human society, can have no hold upon an atheist” (Mendus 1991: 47). He gives his general defense of religious toleration while continuing the anti-Papist rhetoric of the Country party which sought to exclude James II from the throne.

Locke’s arguments for religious toleration connect nicely to his account of civil government. Locke defines life, liberty, health and property as our civil interests. These are the proper concern of a magistrate or civil government. The magistrate can use force and violence where this is necessary to preserve civil interests against attack. This is the central function of the state. One’s religious concerns with salvation, however, are not within the domain of civil interests, and so lie outside of the legitimate concern of the magistrate or the civil government. In effect, Locke adds an additional right to the natural rights of life, liberty, health and property—the right of freedom to choose one’s own road to salvation. (See the section on Toleration in the entry on Locke’s Political Philosophy.)

Locke holds that the use of force by the state to get people to hold certain beliefs or engage in certain ceremonies or practices is illegitimate. The chief means which the magistrate has at her disposal is force, but force is not an effective means for changing or maintaining belief. Suppose then, that the magistrate uses force so as to make people profess that they believe. Locke writes:

A sweet religion, indeed, that obliges men to dissemble, and tell lies to both God and man, for the salvation of their souls! If the magistrate thinks to save men thus, he seems to understand little of the way of salvation; and if he does it not in order to save them, why is he so solicitous of the articles of faith as to enact them by a law? (Mendus 1991: 41)

So, religious persecution by the state is inappropriate. Locke holds that “Whatever is lawful in the commonwealth cannot be prohibited by the magistrate in the church”. This means that the use of bread and wine, or even the sacrificing of a calf could not be prohibited by the magistrate.

If there are competing churches, one might ask which one should have the power? The answer is clearly that power should go to the true church and not to the heretical church. But Locke claims this amounts to saying nothing. For every church believes itself to be the true church, and there is no judge but God who can determine which of these claims is correct. Thus, skepticism about the possibility of religious knowledge is central to Locke’s argument for religious toleration.

Finally, for an account of the influence of Locke’s works, see the supplementary document: Supplement on the Influence of Locke’s Works

Locke’s Works

Oxford University Press is in the process of producing a new edition of all of Locke’s works. This will supersede The Works of John Locke of which the 1823 edition is probably the most standard. The new Clarendon editions began with Peter Nidditch’s edition of An Essay Concerning Human Understanding in 1975. The Oxford Clarendon editions contain much of the material of the Lovelace collection, purchased and donated to Oxford by Paul Mellon. This treasure trove of Locke’s works and letters, which includes early drafts of the Essay and much other material, comes down from Peter King, Locke’s nephew, who inherited Locke’s papers. Access to these papers has given scholars in the twentieth century a much better view of Locke’s philosophical development and provided a window into the details of his activities which is truly remarkable. Hence the new edition of Locke’s works will very likely be definitive.

• [N] An Essay Concerning Human Understanding , Peter H. Nidditch (ed.), 1975. doi:10.1093/actrade/9780198243861.book.1/actrade-9780198243861-book-1
• Some Thoughts Concerning Education , John W. Yolton and Jean S. Yolton (eds.), 1989. doi:10.1093/actrade/9780198245827.book.1/actrade-9780198245827-book-1
• Drafts for the Essay Concerning Human Understanding, and Other Philosophical Writings: In Three Volumes , Vol. 1: Drafts A and B, Peter H. Nidditch and G. A. J. Rogers (eds.), 1990. doi:10.1093/actrade/9780198245452.book.1/actrade-9780198245452-book-1
• The Reasonableness of Christianity: As Delivered in the Scriptures , John C. Higgins-Biddle (ed.), 2000. doi:10.1093/actrade/9780198245254.book.1/actrade-9780198245254-book-1
• An Essay Concerning Toleration: And Other Writings on Law and Politics, 1667–1683 , J. R. Milton and Philip Milton (eds.), 2006. doi:10.1093/actrade/9780199575732.book.1/actrade-9780199575732-book-1
• Vindications of the Reasonableness of Christianity , Victor Nuovo (ed.), 2012. doi:10.1093/actrade/9780199286553.book.1/actrade-9780199286553-book-1
• volume 1, 1987. doi:10.1093/actrade/9780198248019.book.1/actrade-9780198248019-book-1
• volume 2, 1987. doi:10.1093/actrade/9780198248064.book.1/actrade-9780198248064-book-1
• Volume 1, 1991. doi:10.1093/actrade/9780198245469.book.1/actrade-9780198245469-book-1
• Volume 2, 1991,. doi:10.1093/actrade/9780198248378.book.1/actrade-9780198248378-book-1
• Vol. 1: Introduction; Letters Nos. 1–461 , 2010. doi:10.1093/actrade/9780199573615.book.1/actrade-9780199573615-book-1
• Vol. 2: Letters Nos. 462–848 , 1976. doi:10.1093/actrade/9780198245599.book.1/actrade-9780198245599-book-1
• Vol. 3: Letters Nos. 849–1241 , 1978. doi:10.1093/actrade/9780198245605.book.1/actrade-9780198245605-book-1
• Vol. 4: Letters Nos. 1242–1701 , 1978. doi:10.1093/actrade/9780198245612.book.1/actrade-9780198245612-book-1.
• Vol. 5: Letters Nos. 1702–2198 , 1979. doi:10.1093/actrade/9780198245629.book.1/actrade-9780198245629-book-1
• Vol. 6: Letters Nos. 2199–2664 , 1980. doi:10.1093/actrade/9780198245636.book.1/actrade-9780198245636-book-1
• Vol. 7: Letters Nos. 2665–3286 , 1981. doi:10.1093/actrade/9780198245643.book.1/actrade-9780198245643-book-1
• Vol. 8: Letters Nos. 3287–3648 , 1989. doi:10.1093/actrade/9780198245650.book.1/actrade-9780198245650-book-1

In addition to the Oxford Press edition, there are a few editions of some of Locke’s works which are worth noting.

• An Early Draft of Locke’s Essay, Together with Excerpts from his Journal , Richard I. Aaron and Jocelyn Gibb (eds.), Oxford: Clarendon Press, 1936.
• John Locke, Two Tracts of Government , Phillip Abrams (ed.), Cambridge: Cambridge University Press, 1967.
• Locke’s The Two Treatises of Civil Government , Richard Ashcraft (ed.), London: Routledge, 1987.
• [Axtell 1968], The Educational Writings of John Locke: A Critical Edition , James L. Axtell (ed.), Cambridge: Cambridge University Press.
• [Gay 1964], John Locke on Education , Peter Gay (ed.), New York: Bureau of Publications, Columbia Teachers College, 1964.
• Epistola de Tolerantia: A Letter on Toleration , Latin text edited with a preface by Raymond Klibansky; English translation with an introduction and notes by J. W. Gough, Oxford: Oxford University Press, 1968.
• [G&T 1996] “Some Thoughts Concerning Education” and “The Conduct of the Understanding” , Ruth W. Grant and Nathan Tarcov (eds), Indianapolis: Hackett Publishing Co., 1996.
• [Laslett 1960] Locke’s Two Treatises of Government , Peter Laslett (ed.), Cambridge: Cambridge University Press, 1960.
• [Woozley 1964], An Essay Concerning Human Understanding , abridged, A.D. Woozley (ed.), London: Fontana Library, 1964.

Other Primary Sources

• Boyle, Robert, 1675 [1979], “Some Physico-Theological Considerations About the Possibility of the Resurrection”, in Selected Philosophical Papers of Robert Boyle , M.A. Stewart (ed.), New York: Manchester University Press.
• Mill, John Stuart, 1843, A System of Logic Ratiocinative and Inductive , London: John W. Parker.

Biographies

• King, Lord Peter, 1991, The Life of John Locke: with extracts from his correspondence, journals, and common-place books , Bristol: Thoemmes.
• Fox Bourne, H.R., 1876, Life of John Locke , 2 volumes, New York: Harper & Brothers. Reprinted Scientia Aalen, 1969.
• Cranston, Maurice, 1957, John Locke, A Biography , reprinted Oxford: Oxford University Press, 1985.
• Woolhouse, Roger, 2007, Locke: A Biography , Cambridge: Cambridge University Press.

Books and Articles

• Aaron, Richard, 1937, John Locke , Oxford: Oxford University Press.
• Aarsleff, Hans, 1982, From Locke to Saussure: Essays on the Study of Language and Intellectual History , Minneapolis: University of Minnesota Press.
• –––, 1994 “Locke’s Influence”, in Vere Chappell (ed.), The Cambridge Companion to Locke , Cambridge: Cambridge University Press, pp. 252–289. doi:10.1017/CCOL0521383714.011
• Alexander, Peter, 1985, Ideas Qualities and Corpuscles: Locke and Boyle on the External World , Cambridge: Cambridge University Press.
• Alston, William and Jonathan Bennett, 1988, “Locke on People and Substances”, The Philosophical Review , 97(1): 25–46. doi:10.2307/2185098
• Anstey, Peter R., 2011, John Locke and Natural Philosophy , Oxford: Oxford University Press. doi:10.1093/acprof:oso/9780199589777.001.0001
• Armitage, David, 2004, “John Locke, Carolina and the Two Treatises of Government ”, Political Theory , 32(5): 602–27. doi:10.1177/0090591704267122
• Arneil, Barbara, 1996, John Locke and America , Oxford: Clarendon Press.
• Ashcraft, Richard, 1986, Revolutionary Politics and Locke’s Two Treatises of Civil Government , Princeton: Princeton University Press.
• –––, 1992, “Latitudinarianism and Toleration: Historical Myth versus Political History”, in Kroll, Ashcraft, and Zagorin 1992: 151–177. doi:10.1017/CBO9780511896231.008
• Ayers, Michael, 1991, Locke: Epistemology and Ontology , 2 volumes, London: Routledge.
• Barresi, John, and Raymond Martin, 2000, Naturalization of the Soul: Self and Personal Identity in the 18th Century , London: Routledge.
• Bennett, Jonathan, 1971, Locke, Berkeley, Hume: Central Themes , Oxford: Oxford University Press.
• Bolton, Martha Brandt, 2004, “Locke on the Semantic and Epistemic Role of Simple Ideas of Sensation”, Pacific Philosophical Quarterly , 85(3): 301–321. doi:10.1111/j.1468-0114.2004.00200.x
• Brandt, Reinhard (ed.), 1981, John Locke: Symposium Wolfenbuttel 1979 , Berlin: de Gruyter.
• Brewer, Holly, 2017, “Slavery, Sovereignty, and ‘Inheritable Blood’: Reconsidering John Locke and the Origins of American Slavery”, The American Historical Review , 122(4): 1038–1078. doi:10.1093/ahr/122.4.1038
• Chappell, Vere, 1992, Essays on Early Modern Philosophy, John Locke—Theory of Knowledge , London: Garland Publishing, Inc.
• –––, 1994, The Cambridge Companion to Locke , Cambridge: Cambridge University Press.
• –––, 2004a, “Symposium: Locke and the Veil of Perception: Preface”, Pacific Philosophical Quarterly , 85(3): 243–244. doi:10.1111/j.1468-0114.2004.00196.x
• –––, 2004b, “Comments”, Pacific Philosophical Quarterly , 85(3): 338–355. doi:10.1111/j.1468-0114.2004.00202.x
• Chomsky, Noam, 1966, Cartesian Linguistics: A Chapter in the History of Rationalist Thought , New York: Harper & Row.
• Dunn, John, 1969, The Political Thought of John Locke , Cambridge: Cambridge University Press.
• Farr, James, 2008, “Locke, Natural Law and New World Slavery”, Political Theory , 36(4): 495–522. doi:10.1177/0090591708317899
• Fox, Christopher, 1988, Locke and the Scriblerians , Berkeley: University of California Press.
• Garrett, Don, 2003, “Locke on Personal Identity, Consciousness and ‘Fatal Errors’”, Philosophical Topics , 31: 95–125. doi:10.5840/philtopics2003311/214
• Geach, Peter, 1967, “Identity”, The Review of Metaphysics , 21(1): 3–12.
• Gibson, James, 1968, Locke’s Theory of Knowledge and its Historical Relations , Cambridge: Cambridge University Press.
• Gordon-Roth, Jessica, 2015, “Locke’s Place-Time-Kind Principle”, Philosophy Compass , 10(4): 264–274. doi:10.1111/phc3.12217
• Grant, Ruth, 1987, John Locke’s Liberalism , Chicago: University of Chicago Press.
• Gaukroger, Stephen, 2010, The Collapse of Mechanism and the Rise of Sensibility: Science and the Shaping of Modernity 1680–1760 , Oxford, Clarendon Press.
• Kretzmann, Norman, 1968, “The Main Thesis of Locke’s Semantic Theory”, The Philosophical Review , 77(2): 175–196. Reprinted in Tipton 1977: 123–140. doi:10.2307/2183319
• Kroll, Peter, Richard Ashcraft, and Peter Zagorin (eds), 1992, Philosophy, Science and Religion in England 1640–1700 , Cambridge: Cambridge University Press. doi:10.1017/CBO9780511896231
• Jolley, Nicholas, 1984, Leibniz and Locke , Oxford: Oxford University Press.
• –––, 1999, Locke, His Philosophical Thought , Oxford: Oxford University Press.
• –––, 2015, Locke’s Touchy Subjects: Materialism and Immortality , Oxford: Oxford University Press. doi:10.1093/acprof:oso/9780198737094.001.0001
• Laslett, Peter, 1954 [1990], “John Locke as Founder of the Board of Trade”, The Listener , 52(1342): 856–857. Reprinted in J.S. Yolton 1990: 127–136.
• Lennon, Thomas M., 2004, “Through a Glass Darkly: More on Locke’s Logic of Ideas”, Pacific Philosophical Quarterly , 85(3): 322–337. doi:10.1111/j.1468-0114.2004.00203.x
• LoLordo, Antonia, 2010, “Person, Substance, Mode and ‘the moral Man’ in Locke’s Philosophy”, Canadian Journal Of Philosophy , 40(4); 643–668. doi:10.1080/00455091.2010.10716738
• Lott, Tommy, 1998, Subjugation and Bondage: Critical Essays on Slavery and Social Philosophy , New York: Rowman and Littlefield Publishers Inc.
• Lovejoy, Arthur O., 1936, The Great Chain of Being; a Study of the History of an Idea , Cambridge, MA: Harvard University Press.
• Lowe, E.J., 1995, Locke on Human Understanding , London: Routledge Publishing Co.
• Mackie, J. L. 1976, Problems from Locke , Oxford: Clarendon Press.
• Macpherson, C.B., 1962, The Political Theory of Possessive Individualism , Oxford: Oxford University Press.
• Mandelbaum, Maurice, 1966, Philosophy, Science and Sense Perception: Historical and Critical Studies , Baltimore: The John Hopkins University Press.
• Marshall, John, 2006, John Locke, Toleration and Early Enlightenment Culture , Cambridge UK, Cambridge University Press.
• Martin, C. B. and D. M. Armstrong (eds.), 1968, Locke and Berkeley: A Collection of Critical Essays , New York: Anchor Books.
• Mattern, Ruth, 1980, “Moral Science and the Concept of Persons in Locke”, The Philosophical Review , 89(1): 24–45. doi:10.2307/2184862
• McCann, Edwin, 1987, “Locke on Identity, Life, Matter and Consciousness” Archiv für Geschichte der Philosophie , 69(1): 54–77. doi:10.1515/agph.1987.69.1.54
• McLachlan, Hugh, 1941, Religious Opinions of Milton, Locke and Newton , Manchester: Manchester University Press.
• Mendus, Susan, 1991, Locke on Toleration in Focus , London: Routledge.
• Newman, Lex, 2004, “Locke on Sensitive Knowledge and the Veil of Perception—Four Misconceptions”, Pacific Philosophical Quarterly , 85(3): 273–300. doi:10.1111/j.1468-0114.2004.00199.x
• Olsthoorn, Johan and Laurens van Apeldoorn, 2020, “‘This man is my property’: Slavery and political absolutism in Locke and the classical social contract tradition”, European Journal of Political Theory , 21(2): 253–275. doi:10.1177/1474885120911309
• Rogers, G.A. John, 2004, “Locke and the Objects of Perception”, Pacific Philosophical Quarterly , 85(3): 245–254. doi:10.1111/j.1468-0114.2004.00197.x
• Roper, John, April 2004, Conceiving Carolina: Proprietors, Planters and Plots 1662–1729 , New York, Palgrave/Macmillan.
• Russell, Daniel, 2004, “Locke on Land and Labor”, Philosophical Studies , 117(1–2): 303–325. doi:10.1023/B:PHIL.0000014529.01097.20
• Schouls, Peter, 1992, Reasoned Freedom: John Locke and the Enlightenment , Ithaca, NY: Cornell University Press.
• Simmons, A. John, 1992, The Lockean Theory of Rights , Princeton: Princeton University Press.
• Soles, David, 1999, “Is Locke an Imagist?” The Locke Newsletter , 30: 17–66.
• Strawson, Galen, 2011, Locke on Personal Identity , Princeton: Princeton University Press.
• Stuart, Matthew, 2013, Locke’s Metaphysics , Oxford: Oxford University Press. doi:10.1093/acprof:oso/9780199645114.001.0001
• Thiel, Udo, 2011, The Early Modern Subject: Self-Consciousness and Personal Identity from Descartes to Hume , Oxford: Oxford University Press. doi:10.1093/acprof:oso/9780199542499.001.0001
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• Tipton, I.C. (ed.), 1977, Locke on Human Understanding: Selected Essays , Oxford: Oxford University Press.
• Tully, James, 1980, A Discourse on Property , Cambridge: Cambridge University Press.
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• Wilson, Margaret Dauler, 1999, Ideas and Mechanism: Essays on Early Modern Philosophy , Princeton: Princeton University Press.
• Wilson, Thomas D., 2016, The Ashley Cooper Plan: The Founding of Carolina and the Origins of Southern Political Culture , Chapel Hill, NC: University of North Carolina Press.
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• Woolhouse, R.S., 1971, Locke’s Philosophy of Science and Knowledge , New York: Barnes and Noble.
• –––, 1983, Locke , Minneapolis: University of Minnesota Press.
• –––, 1988, The Empiricists , Oxford: Oxford University Press.
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Bibliographies

• Hall, Roland, and Roger Woolhouse, 1983, 80 Years of Locke Scholarship: A Bibliographical Guide , Edinburgh: University of Edinburgh Press.
• Locke Studies (formerly The Locke Newsletter) , edited by Timothy Stanton, Heslington: University of York.

How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

• “John Locke” , entry on Locke, Internet Encyclopedia of Philosophy .
• Images of Locke , National Portrait Gallery, Great Britain.

Berkeley, George | Hume, David | Leibniz, Gottfried Wilhelm | liberalism | Locke, John: moral philosophy | Locke, John: on freedom | Locke, John: on personal identity | Locke, John: philosophy of science | Locke, John: political philosophy | Masham, Lady Damaris | personal identity | substance | tropes

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GREAT THINKERS John Locke

An Essay Concerning Human Understanding

Recommended edition:  An Essay Concerning Human Understanding , ed. Peter H. Nidditch (New York: Oxford University Press, 1975).

Since it is the understanding, that sets man above the rest of sensible beings, and gives him all the advantage and dominion, which he has over them; it is certainly a subject, even for its nobleness, worth our labour to inquire into. The understanding, like the eye, whilst it makes us see and perceive all other things, takes no notice of itself; and it requires art and pains to set it at a distance, and make it its own object. But, whatever be the difficulties that lie in the way of this inquiry; whatever it be, that keeps us so much in the dark to ourselves; sure I am, that all the light we can let in upon our own minds, all the acquaintance we can make with our own understandings, will not only be very pleasant, but bring us great advantage, in directing our thoughts in the search of other things.

This, therefore, being my purpose, to inquire into the original, certainty, and extent of human knowledge; together with the grounds and degrees of belief, opinion, and assent. … It shall suffice to my present purpose, to consider the discerning faculties of a man, as they are employed about the objects, which they have to do with: And I shall imagine I have not wholly misemployed myself in the thoughts I shall have on this occasion, if, in this historical, plain method, I can give any account of the ways, whereby our understandings come to attain those notions of things we have, and can set down any measures of the certainty of our knowledge, or the grounds of those persuasions, which are to be found amongst men, so various, different, and wholly contradictory; and yet asserted, somewhere or other, with such assurance and confidence, that he that shall take a view of the opinions of mankind, observe their opposition, and at the same time consider the fondness and devotion wherewith they are embraced, the resolution and eagerness wherewith they are maintained, may perhaps have reason to suspect, that either there is no such thing as truth at all; or that mankind hath no sufficient means to attain a certain knowledge of it.

It is, therefore, worth while to search out the bounds between opinion and knowledge; and examine by what measures, in things, whereof we have no certain knowledge, we ought to regulate our assent, and moderate our persuasions.

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The first amendment, historic document, an essay concerning human understanding (1690).

John Locke | 1690

John Locke (1632-1704) was the author of A Letter Concerning Toleration (1689), An Essay concerning Human Understanding (1690), Two Treatises on Government (1690), and other works. Prior to the American Revolution, Locke was best known in America for his epistemological work. Contrary to the Cartesian view of innate ideas, Locke claimed that the human mind is a tabula rasa and that knowledge is accessible to us through sense perception and experience. Of the significance of Locke’s contribution to the theory of knowledge, James Madison compared him to Sir Isaac Newton’s discoveries in natural science: Both established “immortal systems, the one [Newton] in matter, the other [Locke] in mind” ("Spirit of Governments," 1791). 

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CHAP. II.: No Innate Principles in the Mind.

The way shewn how we come by any knowledge, sufficient to prove it not innate.

§ 1. It is an established opinion amongst some men, that there are in the understanding certain innate principles; some primary notions, ϰοιναὶ ἔννοιαι, characters, as it were, stamped upon the mind of man, which the soul receives in its very first being; and brings into the world with it. It would be sufficient to convince unprejudiced readers of the falseness of this supposition, if I should only shew (as I hope I shall in the following parts of this discourse) how men, barely by the use of their natural faculties, may attain to all the knowledge they have, without the help of any innate impressions; and may arrive at certainty, without any such original notions or principles. For I imagine any one will easily grant, that it would be impertinent to suppose, the ideas of colours innate in a creature, to whom God hath given sight, and a power to receive them by the eyes, from external objects: and no less unreasonable would it be to attribute several truths to the impressions of nature, and innate characters, when we may observe in ourselves faculties, fit to attain as easy and certain knowledge of them, as if they were originally imprinted on the mind. . . .

CHAP. I: Of Idea in general, and their Original.

§ 2. Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas: —How comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from EXPERIENCE. In that all our knowledge is founded, and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, do spring. . . .

CHAP. XI.: Of Discerning, and other Operations of the Mind.

§ 17. I pretend not to teach, but to inquire, and therefore cannot but confess here again, that external and internal sensation are the only passages that I can find of knowledge to the understanding. These alone, as far as I can discover, are the windows by which light is let into this dark room: for methinks the understanding is not much unlike a closet wholly shut from light, with only some little opening left, to let in external visible resemblances, or ideas of things without: would the pictures coming into such a dark room but stay there, and lie so orderly as to be found upon occasion, it would very much resemble the understanding of a man, in reference to all objects of sight, and the ideas of them. . . .

CHAP. XXI.: Of Power.

§ 51. As therefore the highest perfection of intellectual nature lies in a careful and constant pursuit of true and solid happiness, so the care of ourselves, that we mistake not imaginary for real happiness, is the necessary foundation of our liberty. The stronger ties we have to an unalterable pursuit of happiness in general, which is our greatest good, and which, as such, our desires always follow, the more are we free from any necessary determination of our will to any particular action, and from a necessary compliance with our desire, set upon any particular, and then appearing preferable good, till we have duly examined, whether it has a tendency to, or be inconsistent with our real happiness: and therefore till we are as much informed upon this inquiry, as the weight of the matter, and the nature of the case demands; we are, by the necessity of preferring and pursuing true happiness as our greatest good, obliged to suspend the satisfaction of our desires in particular cases.

§ 52. This is the hinge on which turns the liberty of intellectual beings, in their constant endeavours after and a steady prosecution of true felicity, that they can suspend this prosecution in particular cases, till they have looked before them, and informed themselves whether that particular thing, which is then proposed or desired, lie in the way to their main end, and make a real part of that which is their greatest good: for the inclination and tendency of their nature to happiness is an obligation and motive to them, to take care not to mistake or miss it; and so necessarily puts them upon caution, deliberation, and wariness, in the direction of their particular actions, which are the means to obtain it. Whatever necessity determines to the pursuit of real bliss, the same necessity with the same force establishes suspense, deliberation, and scrutiny of each successive desire, whether the satisfaction of it does not interfere with our true happiness, and mislead us from it. This, as seems to me, is the great privilege of finite intellectual beings; and I desire it may be well considered, whether the great inlet and exercise of all the liberty men have, are capable of, or can be useful to them, and that whereon depends the turn of their actions, does not lie in this, that they can suspend their desires, and stop them from determining their wills to any action, till they have duly and fairly examined the good and evil of it, as far forth as the weight of the thing requires.

 § 2. . . . Sense and intuition reach but a very little way. The greatest part of our knowledge depends upon deductions and intermediate ideas: and in those cases, where we are fain to substitute assent instead of knowledge, and take propositions for true, without being certain they are so, we have need to find out, examine, and compare the grounds of their probability. In both these cases, the faculty which finds out the means, and rightly applies them to discover certainty in the one, and probability in the other, is that which we call reason. For as reason perceives the necessary and indubitable connexion of all the ideas or proofs one to another, in each step of any demonstration that produces knowledge: so it likewise perceives the probable connexion of all the ideas or proofs one to another, in every step of a discourse, to which it will think assent due. This is the lowest degree of that which can be truly called reason. . . .

§ 23. By what has been before said of reason, we may be able to make some guess at the distinction of things, into those that are according to, above, and contrary to reason. 1. According to reason are such propositions, whose truth we can discover by examining and tracing those ideas we have from sensation and reflection; and by natural deduction find to be true or probable. 2. Above reason are such propositions, whose truth or probability we cannot by reason derive from those principles. 3. Contrary to reason are such propositions, as are inconsistent with, or irreconcileable to, our clear and distinct ideas. Thus the existence of one God is according to reason; the existence of more than one God, contrary to reason; the resurrection of the dead, above reason. . . .

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A Summary and Analysis of John Locke’s An Essay Concerning Human Understanding

By Dr Oliver Tearle (Loughborough University)

Published in 1689 though formally dated 1690, John Locke’s An Essay Concerning Human Understanding is one of the most important works of Enlightenment philosophy: indeed, in many ways, Locke paved the way for the (later) Enlightenment.

But what is it about An Essay Concerning Human Understanding , and Locke’s argument, which makes him so important?

You can read the whole of An Essay Concerning Human Understanding here (the text is taken from the original 1689 edition, which erroneously gave the title as An Essay Concerning Humane Understanding ), but we’ve tried to summarise the main points of Locke’s argument below, before proceeding to an analysis of his meaning – and his significance.

An Essay Concerning Human Understanding : summary

Locke begins the Essay by arguing against the earlier rationalist idea (propounded by Descartes among others) that ideas can be innate within the human mind. For Locke, when babies are born their minds are empty: a notion which he famously calls the tabula rasa (literally, ‘blank slate’). Human minds are like a blank sheet of paper when we’re born, and everything that ends up in them is supplied by experience.

This signals Locke’s adherence to empiricism over rationalism: rather than believing knowledge and ideas about the world are in-built within us by nature, he believes that ideas are acquired from external stimuli, from us going out there into the world and being exposed to things.

Book II develops this idea in more detail. Experience is the bedrock of all human knowledge. We don’t inherently ‘know’ things: we learn about things as we experience them. This is a bit like a ‘nurture over nature’ view. There are two routes to knowledge via experience: sensation and reflection . Sensation is about coming into contact with the external world, whereas reflection comes from introspection, or from reflecting on what we have experienced.

Book III proposes an idea later developed in more depth by Immanuel Kant: that we cannot ever know true reality, only our perception of it. And our perception of reality is necessarily subjective: you don’t have precisely the same experience of the world as I do. It is also in Book III that Locke attempts to apply his empiricist approach to language.

Book IV appears, on the face of it, to contradict what Locke had set out to argue: namely, that empiricism rather than rationalism is the correct way to view knowledge. But he is actually arguing that, once we adopt an empirical mindset, we are then able to draw a rationalist conclusion of the world from that experience.

An Essay Concerning Human Understanding : analysis

The twentieth-century philosopher Isaiah Berlin once suggested that John Locke effectively invented the idea of common sense in matters of philosophy, and An Essay Concerning Human Understanding is certainly a powerful defence of the importance of an empiricist outlook, whereby we trust our own senses and experiences rather than simply assuming things to be innately true and unquestionable. Bertrand Russell made a similar claim about Locke’s book.

What this means is that Locke’s contribution to philosophy lies partly in his emphasis on the importance of experience in forming our ideas and values. Empiricism places the emphasis on our own sensory understanding of the world (what is now sometimes called ‘lived experience’, to offer a broader term).

This means that we trust our own senses rather than some innate knowledge we come pre-programmed with at birth. How do we know right from wrong? Locke would argue that we have to learn what ‘right’ and ‘wrong’ mean in order to know that.

Locke is, of course, right to emphasise the importance of experience in forming our knowledge of the world. But, in his determination to oppose the rationalist approach touted by Spinoza, Descartes, and others, does he take things too far in the other direction?

There are many moral philosophers who would argue that we do have an innate sense of right and wrong which is present at birth, even if we’re too young to act on it as soon as we leave the womb. Evolutionary biologists would argue that we wouldn’t have got as far as we have as a species without this in-built sense of morality, among other things.

There are other aspects of An Essay Concerning Human Understanding which critics have argued are too reductive. Although our own experience is obviously important in shaping our view of the world, few would go so far as Locke and argue that it’s the only significant factor.

For one thing, our experience of the world is just too different: a man living in a secluded monastery in Yorkshire is unlikely to arrive at the same ‘knowledge’ of the world as a midwife working in London. Locke grants that our experiences will necessarily be subjective, but where does that leave us when considering supposedly self-evident or universal truths, such as ‘killing is wrong’ or ‘do unto others as you would have them to do you’?

Nevertheless, An Essay Concerning Human Understanding is an important book, not least because it was a milestone in philosophy and would act as the foundation for the work of many philosophers who came after Locke.

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6 John Locke’s (1632–1704) Essay Concerning Human Understanding (1689)

The project of the essay, against innate knowledge, ideas and their origin, simple ideas, primary and secondary qualities, complex ideas, substance/substratum, natural kinds, personal identity, the limits of knowledge.

As Locke admits, his Essay is something of a mess, from an editorial point of view. What follows are what I take to be some of the most important passages from the book, grouped under topical headings in an attempt to make a coherent and systematic whole. Parts and headings are given in bold and are purely my invention. Section headings are given in italics, and are Locke’s. Otherwise, all material in italics is mine, not Locke’s. ‘…’ indicates an omission.

The Essay is organized into Books, Chapters, and Sections. The start of each section cites book.chapter.section. For example, ‘I.i.5’ means Book I, chapter i, section 5.

(Textual note: the standard edition of the Essay is that of P.H. Nidditch (Oxford, 1975); but Roger Woolhouse’s Penguin edition is superior in some respects.)

<!–The headings are as follows: A. The Project B. Against Innate Knowledge C. Ideas and their Origin D. Simple Ideas E. Primary and Secondary Qualities F. Complex Ideas G. Substance/substratum H. Natural Kinds I. Body J. Mind K. Personal Identity L. The Limits of Knowledge M. God–>

(From The Epistle to the Reader ) Were it fit to trouble thee with the history of this Essay, I should tell thee, that five or six friends meeting at my chamber, and discoursing on a subject very remote from this, found themselves quickly at a stand, by the difficulties that rose on every side. After we had awhile puzzled ourselves, without coming any nearer a resolution of those doubts which perplexed us, it came into my thoughts that we took a wrong course; and that before we set ourselves upon inquiries of that nature, it was necessary to examine our own abilities, and see what objects our understandings were, or were not, fitted to deal with. …

The commonwealth of learning is not at this time without master-builders, whose mighty designs, in advancing the sciences, will leave lasting monuments to the admiration of posterity: but every one must not hope to be a Boyle or a Sydenham; and in an age that produces such masters as the great Huygenius and the incomparable Mr. Newton, with some others of that strain, it is ambition enough to be employed as an under-labourer in clearing the ground a little, and removing some of the rubbish that lies in the way to knowledge …

(From I.i.1— An Inquiry into the Understanding pleasant and useful ) Since it is the understanding that sets man above the rest of sensible beings, and gives him all the advantage and dominion which he has over them; it is certainly a subject, even for its nobleness, worth our labour to inquire into. The understanding, like the eye, whilst it makes us see and perceive all other things, takes no notice of itself; and it requires and art and pains to set it at a distance and make it its own object. …

(From I.i.2— Design ) This, therefore, being my purpose–to inquire into the original, certainty, and extent of human knowledge , together with the grounds and degrees of belief , opinion , and assent …

(From I.i.3— Method ) It is therefore worth while to search out the bounds between opinion and knowledge; and examine by what measures, in things whereof we have no certain knowledge, we ought to regulate our assent and moderate our persuasion. In order whereunto I shall pursue this following method: First, I shall inquire into the original of those ideas, notions, or whatever else you please to call them, which a man observes, and is conscious to himself he has in his mind; and the ways whereby the understanding comes to be furnished with them. Secondly, I shall endeavour to show what knowledge the understanding hath by those ideas; and the certainty, evidence, and extent of it. Thirdly, I shall make some inquiry into the nature and grounds of faith or opinion : whereby I mean that assent which we give to any proposition as true, of whose truth yet we have no certain knowledge. And here we shall have occasion to examine the reasons and degrees of assent .

(From I.i.4— Useful to know the Extent of our Comprehension ) If we can find out how far the understanding can extend its view; how far it has faculties to attain certainty; and in what cases it can only judge and guess, we may learn to content ourselves with what is attainable by us in this state.

(From I.i.5— Our Capacity suited to our State and Concerns ) It will be no excuse to an idle and untoward servant, who would not attend his business by candle light, to plead that he had not broad sunshine. The Candle that is set up in us shines bright enough for all our purposes.

(From I.i.6— Knowledge of our Capacity a Cure of Scepticism and Idleness ) When we know our own strength, we shall the better know what to undertake with hopes of success; and when we have well surveyed the powers of our own minds, and made some estimate what we may expect from them, we shall not be inclined either to sit still, and not set our thoughts on work at all, in despair of knowing anything; nor on the other side, question everything, and disclaim all knowledge, because some things are not to be understood. It is of great use to the sailor to know the length of his line, though he cannot with it fathom all the depths of the ocean. It is well he knows that it is long enough to reach the bottom, at such places as are necessary to direct his voyage, and caution him against running upon shoals that may ruin him. Our business here is not to know all things, but those which concern our conduct. If we can find out those measures, whereby a rational creature, put in that state in which man is in this world, may and ought to govern his opinions, and actions depending thereon, we need not to be troubled that some other things escape our knowledge.

• What is Locke’s main project in the Essay?
• What’s the point of pursuing it? What advantages does he expect to obtain from it?
• What is distinctive about Locke’s project? What would Locke think of the method of, say, Spinoza?

Given Locke’s project, it makes sense that he begins by attacking the doctrine of innate knowledge. This attack was partly responsible for the Essay ’s being banned at Oxford in 1704. Can you think why these thoughts might sound dangerous, and why Locke’s project begins where it does?

(From I.ii.5– Not on Mind naturally imprinted, because not known to Children, Idiots, &c. ) For, first, it is evident, that all children and idiots have not the least apprehension or thought of them. And the want of that is enough to destroy that universal assent which must needs be the necessary concomitant of all innate truths: it seeming to me near a contradiction to say, that there are truths imprinted on the soul, which it perceives or understands not: imprinting, if it signify anything, being nothing else but the making certain truths to be perceived. For to imprint anything on the mind without the mind’s perceiving it, seems to me hardly intelligible. If therefore children and idiots have souls, have minds, with those impressions upon them, they must unavoidably perceive them …

[I]f the capacity of knowing be the natural impression contended for, all the truths a man ever comes to know will, by this account, be every one of them innate; and this great point will amount to no more, but only to a very improper way of speaking; which, whilst it pretends to assert the contrary, says nothing different from those who deny innate principles. For nobody, I think, ever denied that the mind was capable of knowing several truths.

(From I.ii.15— The Steps by which the Mind attains several Truths ) The senses at first let in particular ideas, and furnish the yet empty cabinet, and the mind by degrees growing familiar with some of them, they are lodged in the memory, and names got to them. Afterwards, the mind proceeding further, abstracts them, and by degrees learns the use of general names. In this manner the mind comes to be furnished with ideas and language, the materials about which to exercise its discursive faculty. And the use of reason becomes daily more visible, as these materials that give it employment increase. But though the having of general ideas and the use of general words and reason usually grow together, yet I see not how this any way proves them innate.

(From I.iv.20— No innate Ideas in the Memory ) To which let me add: if there be any innate ideas, any ideas in the mind which the mind does not actually think on, they must be lodged in the memory; and from thence must be brought into view by remembrance; i.e., must be known, when they are remembered, to have been perceptions in the mind before; unless remembrance can be without remembrance. For, to remember is to perceive anything with memory, or with a consciousness that it was perceived or known before. Without this, whatever idea comes into the mind is new, and not remembered; this consciousness of its having been in the mind before, being that which distinguishes remembering from all other ways of thinking.

Whatever idea was never perceived by the mind was never in the mind. Whatever idea is in the mind, is, either an actual perception, or else, having been an actual perception, is so in the mind that, by the memory, it can be made an actual perception again. Whenever there is the actual perception of any idea without memory, the idea appears perfectly new and unknown before to the understanding. Whenever the memory brings any idea into actual view, it is with a consciousness that it had been there before, and was not wholly a stranger to the mind. Whether this be not so, I appeal to every one’s observation. And then I desire an instance of an idea, pretended to be innate, which (before any impression of it by ways hereafter to be mentioned) any one could revive and remember, as an idea he had formerly known; without which consciousness of a former perception there is no remembrance; and whatever idea comes into the mind without that consciousness is not remembered, or comes not out of the memory, nor can be said to be in the mind before that appearance. For what is not either actually in view or in the memory, is in the mind no way at all, and is all one as if it had never been there. …

[W]hatever idea, being not actually in view, is in the mind, is there only by being in the memory; and if it be not in the memory, it is not in the mind; and if it be in the memory, it cannot by the memory be brought into actual view without a perception that it comes out of the memory; which is this, that it had been known before, and is now remembered. If therefore there be any innate ideas, they must be in the memory, or else nowhere in the mind; and if they be in the memory, they can be revived without any impression from without; and whenever they are brought into the mind they are remembered, i. E. They bring with them a perception of their not being wholly new to it. …

By this it may be tried whether there be any innate ideas in the mind before impression from sensation or reflection. I would fain meet with the man who, when he came to the use of reason, or at any other time, remembered any of them; and to whom, after he was born, they were never new. If any one will say, there are ideas in the mind that are not in the memory, I desire him to explain himself, and make what he says intelligible.

• Why is Locke concerned to deny the doctrine of innate principles? Can you connect this with Locke’s project?
• Can you extract an argument from these texts that might apply to innate ideas (as opposed to principles)? There seem to be three possible ways to cash out what it means to say that an idea is innate. It might be innate as a capacity; it might always be present to the mind; or it might be lodged in the memory. What does Locke think is wrong with this last option (memory)? (See esp. Chapter 4, Section 20 above—hint: Locke seems to think there’s something contradictory about innateness.)

Premise 1: An innate idea is in the memory. Premise 2: Any idea in the memory, when recovered, brings with it…

It’s one thing to attack the doctrines of innate knowledge and innate ideas; it’s another to come up with a replacement for them. Locke must explain how all our ideas are generated solely out of the materials given to us in experience, and how experience alone can justify our knowledge claims.

(From I.1.8— What Idea stands for ) Thus much I thought necessary to say concerning the occasion of this inquiry into human understanding. But, before I proceed on to what I have thought on this subject, I must here in the entrance beg pardon of my reader for the frequent use of the word idea , which he will find in the following treatise. It being that term which, I think, serves best to stand for whatsoever is the object of the understanding when a man thinks, I have used it to express whatever is meant by phantasm, notion, species , or whatever it is which the mind can be employed about in thinking ; and I could not avoid frequently using it. I presume it will be easily granted me, that there are such ideas in men’s minds: every one is conscious of them in himself; and men’s words and actions will satisfy him that they are in others.

(From IV.xxi.4) [S]ince the things the mind contemplates are none of them, besides itself, present to the understanding, it is necessary that something else, as a sign or representation of the thing it considers, should be present to it: and these are ideas .

(From II.i.2— All Ideas come from Sensation or Reflection ) Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas: how comes it to be furnished? … To this I answer, in one word, from experience . In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.

(From II.i.3— The Objects of Sensation one Source of Ideas ) First, our senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them. And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities …

(From II.i.4— The Operations of our Minds, the other Source of them ) Secondly, the other fountain from which experience furnisheth the understanding with ideas is, the perception of the operations of our own mind within us, as it is employed about the ideas it has got. … And such are perception, thinking, doubting, believing, reasoning, knowing, willing, and all the different actings of our own minds …

(From II.i.5— All our Ideas are of the one or of the other of these ) … These, when we have taken a full survey of them, and their several modes, and the compositions made out of them we shall find to contain all our whole stock of ideas; and that we have nothing in our minds which did not come in one of these two ways. Let any one examine his own thoughts, and thoroughly search into his understanding; and then let him tell me, whether all the original ideas he has there, are any other than of the objects of his senses, or of the operations of his mind, considered as objects of his reflection.

Locke thinks that sensation and reflection are our only sources of ideas. We should now look at his response to Descartes’s argument for a third source of ideas, namely, the intellect (see the second paragraph of the Sixth Meditation .

(From II.xxix.13— Complex ideas may be distinct in one part, and confused in another ) Our complex ideas, being made up of collections, and so variety of simple ones, may accordingly be very clear and distinct in one part, and very obscure and confused in another. In a man who speaks of a chiliaedron, or a body of a thousand sides, the ideas of the figure may be very confused, though that of the number be very distinct; so that he being able to discourse and demonstrate concerning that part of his complex idea which depends upon the number of thousand, he is apt to think he has a distinct idea of a chiliaedron; though it be plain he has no precise idea of its figure, so as to distinguish it, by that, from one that has but 999 sides: the not observing whereof causes no small error in men’s thoughts, and confusion in their discourses.

• How does Locke respond to Descartes’s argument for the distinction between the intellect and the imagination? Who is right?

(From II.i.1— Uncompounded Appearances ) The better to understand the nature, manner, and extent of our knowledge, one thing is carefully to be observed concerning the ideas we have; and that is, that some of them, are simple and some complex .

Though the qualities that affect our senses are, in the things themselves, so united and blended, that there is no separation, no distance between them; yet it is plain, the ideas they produce in the mind enter by the senses simple; and unmixed. For, though the sight and touch often take in from the same object, at the same time, different ideas;–as a man sees at once motion and colour; the hand feels softness and warmth in the same piece of wax: yet the simple ideas thus united in the same subject, are as perfectly distinct as those that come in by different senses.

(From II.iii.1— Division of simple ideas ) The better to conceive the ideas we receive from sensation, it may not be amiss for us to consider them, in reference to the different ways whereby they make their approaches to our minds, and make themselves perceivable by us. First , then, there are some which come into our minds by one sense only . Secondly , there are others that convey themselves into the mind by more senses than one . Thirdly , others that are had from reflection only . Fourthly , there are some that make themselves way, and are suggested to the mind by all the ways of sensation and reflection .

• the idea of blue ___________
• the idea of square ___________
• the idea of hoping ___________
• the idea of straight ___________

(From II.xxi.1— This Idea [of power] how got ) The mind being every day informed, by the senses, of the alteration of those simple ideas it observes in things without; and taking notice how one comes to an end, and ceases to be, and another begins to exist which was not before; reflecting also on what passes within itself, and observing a constant change of its ideas, sometimes by the impression of outward objects on the senses, and sometimes by the determination of its own choice; and concluding from what it has so constantly observed to have been, that the like changes will for the future be made in the same things, by like agents, and by the like ways, considers in one thing the possibility of having any of its simple ideas changed, and in another the possibility of making that change; and so comes by that idea which we call power . Thus we say, fire has a power to melt gold, i.e., to destroy the consistency of its insensible parts, and consequently its hardness, and make it fluid … In which, and the like cases, the power we consider is in reference to the change of perceivable ideas. For we cannot observe any alteration to be made in, or operation upon anything, but by the observable change of its sensible ideas; nor conceive any alteration to be made, but by conceiving a change of some of its ideas.

(From II.xxi.2— Power, active and passive ) Power thus considered is two-fold, viz. As able to make, or able to receive any change. The one may be called active , and the other passive power. Whether matter be not wholly destitute of active power, as its author, God, is truly above all passive power; and whether the intermediate state of created spirits be not that alone which is capable of both active and passive power, may be worth consideration. I shall not now enter into that inquiry, my present business being not to search into the original of power, but how we come by the idea of it. But since active powers make so great a part of our complex ideas of natural substances, (as we shall see hereafter,) and I mention them as such, according to common apprehension; yet they being not, perhaps, so truly active powers as our hasty thoughts are apt to represent them, I judge it not amiss, by this intimation, to direct our minds to the consideration of god and spirits, for the clearest idea of active power.

(From II.xxi.3— Power includes Relation ) I confess power includes in it some kind of relation (a relation to action or change,) as indeed which of our ideas of what kind soever, when attentively considered, does not. For, our ideas of extension, duration, and number, do they not all contain in them a secret relation of the parts? figure and motion have something relative in them much more visibly. … Our idea therefore of power, I think, may well have a place amongst other simple ideas , and be considered as one of them; being one of those that make a principal ingredient in our complex ideas of substances, as we shall hereafter have occasion to observe.

(From II.xxi.4— The clearest Idea of active Power had from Spirit ) [I]f we will consider it attentively, bodies, by our senses, do not afford us so clear and distinct an idea of active power, as we have from reflection on the operations of our minds. For all power relating to action, and there being but two sorts of action whereof we have an idea, viz. Thinking and motion, let us consider whence we have the clearest ideas of the powers which produce these actions.

Of thinking, body affords us no idea at all; it is only from reflection that we have that. Neither have we from body any idea of the beginning of motion. A body at rest affords us no idea of any active power to move; and when it is set in motion itself, that motion is rather a passion than an action in it. For, when the ball obeys the motion of a billiard-stick, it is not any action of the ball, but bare passion. Also when by impulse it sets another ball in motion that lay in its way, it only communicates the motion it had received from another, and loses in itself so much as the other received: which gives us but a very obscure idea of an active power of moving in body, whilst we observe it only to transfer , but not produce any motion.

• Is the idea of power a simple idea or not? What turns on this?
• How does the mind form an idea of power?
• Why does sensation not give us an idea of active power?

II.viii is intended as a further discussion of simple ideas. Locke draws what should by now be a familiar distinction. Can you reconstruct Locke’s argument?

(From II.viii.7— Ideas in the Mind, Qualities in Bodies ) To discover the nature of our ideas the better, and to, discourse of them intelligibly, it will be convenient to distinguish them as they are ideas or perceptions in our minds ; and as they are modifications of matter in the bodies that cause such perceptions in us …

(From II.viii.8— Our Ideas and the Qualities of Bodies ) Whatsoever the mind perceives in itself , or is the immediate object of perception, thought, or understanding, that I call idea ; and the power to produce any idea in our mind, I call quality of the subject wherein that power is. Thus a snowball having the power to produce in us the ideas of white, cold, and round—the power to produce those ideas in us, as they are in the snowball, I call qualities; and as they are sensations or perceptions in our understandings, I call them ideas; which ideas , if I speak of sometimes as in the things themselves, I would be understood to mean those qualities in the objects which produce them in us.

(From II.viii.9— Primary Qualities of Bodies ) Concerning these qualities, we, I think, observe these primary ones in bodies that produce simple ideas in us, viz. solidity, extension, motion or rest , nubmer or figure . These, which I call original or primary qualities of body, are wholly inseparable from it; and such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps; and such as sense constantly finds in every particle of matter which has bulk enough to be perceived; and the mind finds inseparable from every particle of matter, though less than to make itself singly be perceived by our senses: e.g., take a grain of wheat, divide it into two parts; each part has still solidity, extension, figure, and mobility: divide it again, and it retains still the same qualities …

(From II.viii.11— How Bodies produce Ideas in us ) The next thing to be considered is, how bodies operate one upon another; and that is manifestly by impulse, and nothing else. It being impossible to conceive that body should operate on what it does not touch (which is all one as to imagine it can operate where it is not), or when it does touch, operate any other way than by motion.

(From II.viii.13— How secondary Qualities produce their ideas ) After the same manner that the ideas of these original qualities are produced in us, we may conceive that the ideas of secondary qualities are also produced, viz. By the operation of insensible particles on our senses. … [L]et us suppose at present that, the different motions and figures, bulk and number, of such particles, affecting the several organs of our senses, produce in us those different sensations which we have from the colours and smells of bodies … It being no more impossible to conceive that god should annex such ideas to such motions, with which they have no similitude, than that he should annex the idea of pain to the motion of a piece of steel dividing our flesh, with which that idea hath no resemblance.

(From II.viii.14— They depend on the primary Qualities ) What I have said concerning colours and smells may be understood also of tastes and sounds, and other the like sensible qualities; which, whatever reality we by mistake attribute to them, are in truth nothing in the objects themselves, but powers to produce various sensations in us; and depend on those primary qualities, viz. Bulk, figure, texture, and motion of parts and therefore I call them secondary qualities .

(From II.viii.15— Ideas of primary Qualities are Resemblances; of secondary, not ) From whence I think it easy to draw this observation, that the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves, but the ideas produced in us by these secondary qualities have no resemblance of them at all. There is nothing like our ideas, existing in the bodies themselves. They are, in the bodies we denominate from them, only a power to produce those sensations in us …

(From II.viii.17— The ideas of the Primary alone really exist ) The particular bulk, number, figure, and motion of the parts of fire or snow are really in them, whether any one’s senses perceive them or no: and therefore they may be called real qualities, because they really exist in those bodies. But light, heat, whiteness, or coldness, are no more really in them than sickness or pain is in manna. Take away the sensation of them; let not the eyes see light or colours, nor the can hear sounds; let the palate not taste, nor the nose smell, and all colours, tastes, odours, and sounds, as they are such particular ideas , vanish and cease, and are reduced to their causes, i.e., bulk, figure, and motion of parts.

(From II.viii.19— Examples ) Let us consider the red and white colours in porphyry. Hinder light from striking on it, and its colours vanish; it no longer produces any such ideas in us: upon the return of light it produces these appearances on us again. Can any one think any real alterations are made in the porphyry by the presence or absence of light; and that those ideas of whiteness and redness are really in porphyry in the light, when it is plain it has no colour in the dark ? It has, indeed, such a configuration of particles, both night and day, as are apt, by the rays of light rebounding from some parts of that hard stone, to produce in us the idea of redness, and from others the idea of whiteness; but whiteness or redness are not in it at any time, but such a texture that hath the power to produce such a sensation in us.

(From II.viii.20) Pound an almond, and the clear white colour will be altered into a dirty one, and the sweet taste into an oily one. What real alteration can the beating of the pestle make in an body, but an alteration of the texture of it?

(From II.viii.21— Explains how water felt as cold by one hand may be warm to the other ) Ideas being thus distinguished and understood, we may be able to give an account how the same water, at the same time, may produce the idea of cold by one hand and of heat by the other: whereas it is impossible that the same water, if those ideas were really in it, should at the same time be both hot and cold. For, if we imagine warmth , as it is in our hands, to be nothing but a certain sort and degree of motion in the minute particles of our nerves or animal spirits, we may understand how it is possible that the same water may, at the same time, produce the sensations of heat in one hand and cold in the other; which yet figure never does, that never producing the idea of a square by one hand which has produced the idea of a globe by another.

Locke argues for three theses in this chapter:

• Ideas of secondary qualities do not resemble anything in the objects that ‘have’ them
• Secondary qualities depend on primary
• Secondary qualities are nothing but powers in objects to produce certain ideas in us

If there were no observers or perceivers, what would the world be like, according to Locke? That is, what qualities does a physical object have in itself?

How does Locke argue for his three theses? Let’s start with (i): ideas of secondary qualities resemble nothing in the objects.

Recall Aquinas’s picture of (bodily) causation: one object (e.g., fire) produces in another the same kind of quality it has in itself (e.g., heat). Why does Locke think that there isn’t really any heat in the first object? Let’s take a case where fire produces a sensation of heat in a person. If our sensation of heat resembled any quality in the object, that quality would have to be the cause of the heat that it produces.

• Why does Locke reject this? (see especially II.viii.11 above).
• Locke argues for a further thesis:

Why think that the color of an object (i.e., the color ideas it produces in us) depends on its primary qualities? (Hint: use II.viii.20)

Finally, what about thesis (iii): secondary qualities are nothing but powers in objects to produce certain ideas in us? Well, this is just to combine (i) and (ii). If they’re not resemblances, and they depend on the primary qualities, then to say that a body has a particular color is just to say that its parts are so arranged as to produce a given idea in us. (Note that primary qualities are powers and genuine qualities in objects; secondary are merely powers.)

• Think of as many different ways to change the color of this room as you can.

So far, we’ve dealt only with simple ideas. But our experience doesn’t seem to come to us packaged in simple, discrete elements. So Locke needs to deal with how we generate experiences (and thoughts) of ordinary objects—what he calls ‘substances’– out of simple ideas.

(From II.xii.1— Made by the Mind out of simple Ones ) We have hitherto considered those ideas, in the reception whereof the mind is only passive, which are those simple ones received from sensation and reflection before mentioned, whereof the mind cannot make one to itself, nor have any idea which does not wholly consist of them. … Ideas thus made up of several simple ones put together, I call complex .

(From II.xii.2— Made voluntarily ) In this faculty of repeating and joining together its ideas, the mind has great power in varying and multiplying the objects of its thoughts, infinitely beyond what sensation or reflection furnished it with: but all this still confined to those simple ideas which it received from those two sources, and which are the ultimate materials of all its compositions.

(From II.xii.3— Complex ideas are either of Modes, Substances, or Relations )

(From II.xxiii.1— Ideas of substances, how made ) The mind being, as I have declared, furnished with a great number of the simple ideas, conveyed in by the senses as they are found in exterior things, or by reflection on its own operations, takes notice also that a certain number of these simple ideas go constantly together; which being presumed to belong to one thing, and words being suited to common apprehensions, and made use of for quick dispatch are called, so united in one subject, by one name; which, by inadvertency, we are apt afterward to talk of and consider as one simple idea, which indeed is a complication of many ideas together: because, as I have said, not imagining how these simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum wherein they do subsist, and from which they do result, which therefore we call substance .

• List the ideas necessary to construct an idea of a substance like Helga (a dog).

Our simple ideas represent qualities; to think of a substance like a dog, however, we need to think of these qualities as inhering in or being unified by some underlying substratum (which he sometimes also calls ‘pure substance in general’). What is Locke’s attitude toward this substratum, and our knowledge of it?

(From II.xiii.19— Substance and accidents of little use in Philosophy ) They who first ran into the notion of accidents , as a sort of real beings that needed something to inhere in, were forced to find out the word substance to support them. Had the poor Indian philosopher (who imagined that the earth also wanted something to bear it up) but thought of this word substance, he needed not to have been at the trouble to find an elephant to support it, and a tortoise to support his elephant: the word substance would have done it effectually. And he that inquired might have taken it for as good an answer from an Indian philosopher—that substance, without knowing what it is, is that which supports the earth, as take it for a sufficient answer and good doctrine from our european philosophers—that substance, without knowing what it is, is that which supports accidents. So that of substance, we have no idea of what it is, but only a confused obscure one of what it does.

(From II.xiii.20— Sticking on and under-propping ) Whatever a learned man may do here, an intelligent american, who inquired into the nature of things, would scarce take it for a satisfactory account, if, desiring to learn our architecture, he should be told that a pillar is a thing supported by a basis, and a basis something that supported a pillar. Would he not think himself mocked, instead of taught, with such an account as this? … Were the latin words, inhaerentia and substantio , put into the plain english ones that answer them, and were called sticking on and under-propping , they would better discover to us the very great clearness there is in the doctrine of substance and accidents, and show of what use they are in deciding of questions in philosophy.

(From II.xxiii.23— Our obscure Idea of Substance in general ) So that if any one will examine himself concerning his notion of pure substance in general, he will find he has no other idea of it at all, but only a supposition of he knows not what support of such qualities which are capable of producing simple ideas in us; which qualities are commonly called accidents. If any one should be asked, what is the subject wherein colour or weight inheres, he would have nothing to say, but the solid extended parts; and if he were demanded, what is it that solidity and extension adhere in, he would not be in a much better case than the Indian before mentioned who, saying that the world was supported by a great elephant, was asked what the elephant rested on; to which his answer was—a great tortoise: but being again pressed to know what gave support to the broad-backed tortoise, replied— something, he knew not what .

• It’s vital to see that by ‘substance’ Locke means here ‘substratum’: that in which properties inhere. This notion is akin to Aristotle’s notion of prime matter. Why might one say that Locke has a love/hate relationship with substratum?

Now that we know how we think about individual substances (e.g., an elephant), we need to know how we can think about kinds or sorts of things. I’m not limited to thinking (or talking) about individual substances; I can make claims that apply to groups or sorts of substances. Locke’s abstraction is the mechanism by which we move from purely determinate ideas to general ones.

Keep in mind that Locke has two kinds of fish to fry in this context: the Cartesians, who think that the essence of body is just extension, and the Aristotelians, who think that the world presents itself to us as if it were ‘carved at the joints’ into innumerable distinct natural kinds. In this context, Locke’s role as an ‘under-labourer’ to science is most in evidence.

(From III.ii.6— How general Words are made ) … Words become general by being made the signs of general ideas: and ideas become general, by separating from them the circumstances of time and place, and any other ideas that may determine them to this or that particular existence. By this way of abstraction they are made capable of representing more individuals than one; each of which having in it a conformity to that abstract idea, is (as we call it) of that sort.

(From III.ii.7— Shown by the way we enlarge our complex ideas from infancy ) … [T]here is nothing more evident, than that the ideas of the persons children converse with (to instance in them alone) are, like the persons themselves, only particular. The ideas of the nurse and the mother are well framed in their minds; and, like pictures of them there, represent only those individuals. The names they first gave to them are confined to these individuals; and the names of nurse and mamma , the child uses, determine themselves to those persons. Afterwards, when time and a larger acquaintance have made them observe that there are a great many other things in the world, that in some common agreements of shape, and several other qualities, resemble their father and mother, and those persons they have been used to, they frame an idea, which they find those many particulars do partake in; and to that they give, with others, the name man , for example. And thus they come to have a general name, and a general idea. Wherein they make nothing new; but only leave out of the complex idea they had of Peter and James, Mary and Jane, that which is peculiar to each, and retain only what is common to them all.

(From III.iii.11— General and Universal are Creatures of the Understanding, and belong not to the Real Existence of things ) [I]t is plain, by what has been said, that general and universal belong not to the real existence of things; but are the inventions and creatures of the understanding, made by it for its own use, and concern only signs, whether words or ideas. … [I]deas are general when they are set up as the representatives of many particular things: but universality belongs not to things themselves, which are all of them particular in their existence, even those words and ideas which in their signification are general. When therefore we quit particulars, the generals that rest are only creatures of our own making; their general nature being nothing but the capacity they are put into, by the understanding, of signifying or representing many particulars. For the signification they have is nothing but a relation that, by the mind of man, is added to them.

(From III.iii.13— They are the Workmanship of the Understanding, but have their Foundation in the Similitude of Things ) I would not here be thought to forget, much less to deny, that Nature, in the production of things, makes several of them alike: there is nothing more obvious, especially in the races of animals, and all things propagated by seed. But yet I think we may say, the sorting of them under names is the workmanship of the understanding, taking occasion, from the similitude it observes amongst them, to make abstract general ideas , and set them up in the mind, with names annexed to them, as patterns or forms, (for, in that sense, the word form has a very proper signification,) to which as particular things existing are found to agree, so they come to be of that species, have that denomination, or are put into that class .

(From III.iii.15— Several significations of the word Essence ) But since the essences of things are thought by some (and not without reason) to be wholly unknown, it may not be amiss to consider the several significations of the word essence .

Real essences . First, essence may be taken for the very being of anything, whereby it is what it is. And thus the real internal, but generally (in substances) unknown constitution of things, whereon their discoverable qualities depend, may be called their essence. This is the proper original signification of the word, as is evident from the formation of it; essential in its primary notation, signifying properly, being. And in this sense it is still used, when we speak of the essence of particular things, without giving them any name. Nominal essences . Secondly, the learning and disputes of the schools having been much busied about genus and species, the word essence has almost lost its primary signification: and, instead of the real constitution of things, has been almost wholly applied to the artificial constitution of genus and species. It is true, there is ordinarily supposed a real constitution of the sorts of things; and it is past doubt there must be some real constitution, on which any collection of simple ideas co-existing must depend. But, it being evident that things are ranked under names into sorts or species, only as they agree to certain abstract ideas, to which we have annexed those names, the essence of each genus , or sort, comes to be nothing but that abstract idea which the general, or sortal (if I may have leave so to call it from sort, as I do general from genus,) name stands for. And this we shall find to be that which the word essence imports in its most familiar use. These two sorts of essences, I suppose, may not unfitly be termed, the one the real , the other nominal essence .

(From III.iii.17— Supposition, that Species are distinguished by their real Essences useless ) [The opinion that considers] real essences as a certain number of forms or moulds, wherein all natural things that exist are cast, and do equally partake, has, I imagine, very much perplexed the knowledge of natural things. The frequent productions of monsters, in all the species of animals, and of changelings, and other strange issues of human birth, carry with them difficulties, not possible to consist with this hypothesis; since it is as impossible that two things partaking exactly of the same real essence should have different properties, as that two figures partaking of the same real essence of a circle should have different properties. But were there no other reason against it, yet the supposition of essences that cannot be known; and the making of them, nevertheless, to be that which distinguishes the species of things, is so wholly useless and unserviceable to any part of our knowledge, that that alone were sufficient to make us lay it by …

(From III.vi.6— Even the real essences of individual substances imply potential sorts ) It is true, I have often mentioned a real essence , distinct in substances from those abstract ideas of them, which I call their nominal essence. By this real essence I mean, that real constitution of anything, which is the foundation of all those properties that are combined in, and are constantly found to co-exist with the nominal essence; that particular constitution which everything has within itself, without any relation to anything without it. But essence, even in this sense, relates to a sort, and supposes a species . For, being that real constitution on which the properties depend, it necessarily supposes a sort of things, properties belonging only to species, and not to individuals: e.g., supposing the nominal essence of gold to be a body of such a peculiar colour and weight, with malleability and fusibility, the real essence is that constitution of the parts of matter on which these qualities and their union depend; and is also the foundation of its solubility in aqua regia and other properties, accompanying that complex idea. Hre are essences and properties, but all upon supposition of a sort or general abstract idea, which is considered as immutable; but there is no individual parcel of matter to which any of these qualities are so annexed as to be essential to it or inseparable from it.

(From III.vi.50) For, let us consider, when we affirm that ‘all gold is fixed,’ either it means that fixedness is a part of the definition, i.e., part of the nominal essence the word ‘gold’ stands for; and so this affirmation, ‘all gold is fixed,’ contains nothing but the signification of the term ‘gold’.

Or else it means, that fixedness, not being a part of the definition of ‘gold’, is a property of that substance itself: in which case it is plain that the word ‘gold’ stands in the place of a substance, having the real essence of a species of things made by nature. In which way of substitution it has so confused and uncertain a signification, that, though this proposition—‘gold is fixed’—be in that sense an affirmation of something real; yet it is a truth will always fail us in its particular application, and so is of no real use or certainty. For let it be ever so true, that all gold, i.e., all that has the real essence of gold, is fixed, what serves this for, whilst we know not, in this sense, what is or is not gold? For if we know not the real essence of gold, it is impossible we should know what parcel of matter has that essence, and so whether it be true gold or no.

• In this passage, Locke argues that all general claims about kinds (e.g., ‘gold is fixed’) are either trivial or uncertain. Using the gold example, explain each of these alternatives. In what way can it be taken as trivial? As uncertain?

Now that we have some story about how our ideas of substances are constructed, we need to look at the two main kinds of substance we seem to find in the world: mind and body. Notice Locke’s argument against Descartes’s conflation of body and extension. Locke also replies here to Leibniz’s argument against Newtonian space, namely, that it must be either a substance or an accident, and neither makes much sense.

(From II.xiii.17— Cohesion of solid parts and Impulse, the primary ideas peculiar to Body ) The primary ideas we have peculiar to body , as contradistinguished to spirit, are the cohesion of solid, and consequently separable, parts , and a power of communicating motion by impulse . These, I think, are the original ideas proper and peculiar to body; for figure is but the consequence of finite extension.

(From II.xiii.11— Extension and Body not the same ) There are some that would persuade us, that body and extension are the same thing … If, therefore, they mean by body and extension the same that other people do, viz. By body something that is solid and extended, whose parts are separable and movable different ways; and by extension , only the space that lies between the extremities of those solid coherent parts, and which is possessed by them, [then] they confound very different ideas one with another; for I appeal to every man’s own thoughts, whether the idea of space be not as distinct from that of solidity, as it is from the idea of scarlet colour? It is true, solidity cannot exist without extension, neither can scarlet colour exist without extension, but this hinders not, but that they are distinct ideas.

And if it be a reason to prove that spirit is different from body, because thinking includes not the idea of extension in it; the same reason will be as valid, I suppose, to prove that space is not body, because it includes not the idea of solidity in it; space and solidity being as distinct ideas as thinking and extension , and as wholly separable in the mind one from another … Extension includes no solidity, nor resistance to the motion of body, as body does.

(From II.xiii.3— Space and Extension ) This space, considered barely in length between any two beings, without considering anything else between them, is called distance : if considered in length, breadth, and thickness, I think it may be called capacity . When considered between the extremities of matter, which fills the capacity of space with something solid, tangible, and moveable, it is properly called extension . And so extension is an idea belonging to body only; but space may, as is evident, be considered without it.

(From II.xiii.17— Substance, which we know not, no proof against space without body ) If it be demanded (as usually it is) whether this space, void of body, be substance or accident , I shall readily answer I know not; nor shall be ashamed to own my ignorance, till they that ask show me a clear distinct idea of substance.

Locke here sets out the constituent ideas that make up the complex idea of the mind. He also launches an attack against Descartes’s claim that thought is the essence of the soul. Most famously, he denies that we can be sure that what thinks in us in an immaterial substance.

(From II.xxiii.18. Thinking and motivity ) The ideas we have belonging and peculiar to spirit , are thinking , and will , or a power of putting body into motion by thought, and, which is consequent to it, liberty . For, as body cannot but communicate its motion by impulse to another body, which it meets with at rest, so the mind can put bodies into motion, or forbear to do so, as it pleases. The ideas of existence , duration , and mobility , are common to them both.

(From II.i.10— The Soul thinks not always; for this wants Proofs ) … I confess myself to have one of those dull souls, that doth not perceive itself always to contemplate ideas; nor can conceive it any more necessary for the soul always to think, than for the body always to move: the perception of ideas being (as I conceive) to the soul, what motion is to the body; not its essence, but one of its operations. And therefore, though thinking be supposed never so much the proper action of the soul, yet it is not necessary to suppose that it should be always thinking, always in action. … To say that actual thinking is essential to the soul, and inseparable from it, is to beg what is in question, and not to prove it by reason; which is necessary to be done, if it be not a self-evident proposition But whether this, “That the soul always thinks,” be a self-evident proposition, that everybody assents to at first hearing, I appeal to mankind. It is doubted whether I thought at all last night or no. The question being about a matter of fact, it is begging it to bring, as a proof for it, an hypothesis, which is the very thing in dispute: by which way one may prove anything …

But men in love with their opinions may not only suppose what is in question, but allege wrong matter of fact. How else could any one make it an inference of mine, that a thing is not, because we are not sensible of it in our sleep? I do not say there is no soul in a man, because he is not sensible of it in his sleep; but I do say, he cannot think at any time, waking or sleeping, without being sensible of it. Our being sensible of it is not necessary to anything but to our thoughts; and to them it is; and to them it always will be necessary, till we can think without being conscious of it.

• Locke begins with an argument from experience. How does it work? We can think of it as a reductio ad absurdum :

Premise 1: The soul’s essence is to think (Descartes’s view) Premise 2: Given 1, it follows that the soul _______ (since this is part of what it is to be an essential property) Premise 3: But experience shows _______. Conclusion: _______.

Now, Locke realizes that the Cartesian will not leave things at that; he will insist that minds think even during sleep, though they do not remember it. Locke thinks this move has a heavy price:

(From II.i.11— It is not always conscious of [thinking] ) I grant that the soul, in a waking man, is never without thought, because it is the condition of being awake. But whether sleeping without dreaming be not an affection of the whole man, mind as well as body, may be worth a waking man’s consideration; it being hard to conceive that anything should think and not be conscious of it. If the soul doth think in a sleeping man without being conscious of it, I ask whether, during such thinking, it has any pleasure or pain, or be capable of happiness or misery? I am sure the man is not; no more than the bed or earth he lies on. For to be happy or miserable without being conscious of it, seems to me utterly inconsistent and impossible. Or if it be possible that the soul can, whilst the body is sleeping, have its thinking, enjoyments, and concerns, its pleasures or pain, apart, which the man is not conscious of nor partakes in—it is certain that Socrates asleep and Socrates awake is not the same person; but his soul when he sleeps, and Socrates the man, consisting of body and soul, when he is waking, are two persons: since waking Socrates has no knowledge of, or concernment for that happiness or misery of his soul, which it enjoys alone by itself whilst he sleeps, without perceiving anything of it; no more than he has for the happiness or misery of a man in the indies, whom he knows not. For, if we take wholly away all consciousness of our actions and sensations, especially of pleasure and pain, and the concernment that accompanies it, it will be hard to know wherein to place personal identity.

• What price does Locke think Descartes must pay, in order to hang on to his claim that the soul always thinks?

(From II.xxiii.5— As clear an idea of spiritual substance as of corporeal substance ) The same thing happens concerning the operations of the mind, viz. thinking, reasoning, fearing, &c., which we concluding not to subsist of themselves, nor apprehending how they can belong to body, or be produced by it, we are apt to think these the actions of some other substance , which we call spirit ; whereby yet it is evident that, having no other idea or notion of matter, but something wherein those many sensible qualities which affect our senses do subsist; by supposing a substance wherein thinking, knowing, doubting, and a power of moving, &c., do subsist, we have as clear a notion of the substance of spirit, as we have of body; the one being supposed to be (without knowing what it is) the substratum to those simple ideas we have from without; and the other supposed (with a like ignorance of what it is) to be the substratum to those operations we experiment in ourselves within. It is plain then, that the idea of corporeal substance in matter is as remote from our conceptions and apprehensions, as that of spiritual substance , or spirit: and therefore, from our not having, any notion of the substance of spirit, we can no more conclude its non-existence, than we can, for the same reason, deny the existence of body …

(From II.xxiii.16— No Idea of abstract Substance either in Body or Spirit ) By the complex idea of extended, figured, coloured, and all other sensible qualities, which is all that we know of it, we are as far from the idea of the substance of body, as if we knew nothing at all: nor after all the acquaintance and familiarity which we imagine we have with matter, and the many qualities men assure themselves they perceive and know in bodies, will it perhaps upon examination be found, that they have any more or clearer primary ideas belonging to body, than they have belonging to immaterial spirit.

(From II.xxiii.23— Cohesion of solid Parts in Body as hard to be conceived as thinking in a Soul ) [I]f [a man] says he knows not how he thinks, I answer, Neither knows he how he is extended, how the solid parts of body are united or cohere together to make extension. For though the pressure of the particles of air may account for the cohesion of several parts of matter that are grosser than the particles of air, and have pores less than the corpuscles of air, yet the weight or pressure of the air will not explain, nor can be a cause of the coherence of the particles of air themselves. And if the pressure of the aether, or any subtiler matter than the air, may unite, and hold fast together, the parts of a particle of air, as well as other bodies, yet it cannot make bonds for itself , and hold together the parts that make up every the least corpuscle of that materia subtilis .

(From II.xxiii.28— Communication of Motion by Impulse, or by Thought, equally unintelligible ) Another idea we have of body is, the power of communication of motion by impulse ; and of our souls, the power of exciting motion by thought . These ideas, the one of body, the other of our minds, every day’s experience clearly furnishes us with: but if here again we inquire how this is done, we are equally in the dark. For, in the communication of motion by impulse, wherein as much motion is lost to one body as is got to the other, which is the ordinariest case, we can have no other conception, but of the passing of motion out of one body into another; which, I think, is as obscure and inconceivable as how our minds move or stop our bodies by thought, which we every moment find they do. We have by daily experience clear evidence of motion produced both by impulse and by thought; but the manner how, hardly comes within our comprehension: we are equally at a loss in both. So that, however we consider motion, and its communication, either from body or spirit, the idea which belongs to spirit is at least as clear as that which belongs to body. And if we consider the active power of moving, or, as I may call it, motivity, it is much clearer in spirit than body; since two bodies, placed by one another at rest, will never afford us the idea of a power in the one to move the other, but by a borrowed motion. …

• Locke is here raising the problem of transference: how can one body give its motion to another? See Aquinas , Summa Contra Gentiles Chapter Sixty-nine, Section Seven , and Descartes’s Principles (Part II, sections xxiv-v). How would each react to what Locke says here?

(From IV.iii.6— Our Knowledge, therefore narrower than our Ideas ) From all which it is evident, that the extent of our knowledge comes not only short of the reality of things, but even of the extent of our own ideas. Though our knowledge be limited to our ideas, and cannot exceed them either in extent or perfection; … Yet it would be well with us if our knowledge were but as large as our ideas, and there were not many doubts and inquiries concerning the ideas we have , whereof we are not, nor I believe ever shall be in this world resolved. Nevertheless, I do not question but that human knowledge, under the present circumstances of our beings and constitutions, may be carried much further than it has hitherto been, if men would sincerely, and with freedom of mind, employ all that industry and labour of thought, in improving the means of discovering truth, which they do for the colouring or support of falsehood, to maintain a system, interest, or party they are once engaged in.

… We have the ideas of a square , a circle , and equality ; and yet, perhaps, shall never be able to find a circle equal to a square, and certainly know that it is so. We have the ideas of matter and thinking , but possibly shall never be able to know whether [any mere material being] thinks or no; it being impossible for us, by the contemplation of our own ideas, without revelation, to discover whether Omnipotency has not given to some systems of matter, fitly disposed, a power to perceive and think, or else joined and fixed to matter, so disposed, a thinking immaterial substance: it being, in respect of our notions, not much more remote from our comprehension to conceive that God can, if he pleases, superadd to matter a faculty of thinking , than that he should superadd to it another substance with a faculty of thinking ; since we know not wherein thinking consists, nor to what sort of substances the Almighty has been pleased to give that power, which cannot be in any created being, but merely by the good pleasure and bounty of the Creator. For I see no contradiction in it, that the first Eternal thinking Being, or Omnipotent Spirit, should, if he pleased, give to certain systems of created senseless matter, put together as he thinks fit, some degrees of sense, perception, and thought: though, as I think I have proved, lib. iv. Ch. 10, Section 14, &c., it is no less than a contradiction to suppose matter (which is evidently in its own nature void of sense and thought) should be that Eternal first-thinking Being. What certainty of knowledge can any one have, that some perceptions, such as, e.g., pleasure and pain, should not be in some bodies themselves, after a certain manner modified and moved, as well as that they should be in an immaterial substance, upon the motion of the parts of body: Body, as far as we can conceive, being able only to strike and affect body, and motion, according to the utmost reach of our ideas, being able to produce nothing but motion; so that when we allow it to produce pleasure or pain, or the idea of a colour or sound, we are fain to quit our reason, go beyond our ideas, and attribute it wholly to the good pleasure of our Maker. For, since we must allow He has annexed effects to motion which we can no way conceive motion able to produce, what reason have we to conclude that He could not order them as well to be produced in a subject we cannot conceive capable of them, as well as in a subject we cannot conceive the motion of matter can any way operate upon? I say not this, that I would any way lessen the belief of the soul’s immateriality: I am not here speaking of probability, but knowledge, and I think not only that it becomes the modesty of philosophy not to pronounce magisterially, where we want that evidence that can produce knowledge; but also, that it is of use to us to discern how far our knowledge does reach; for the state we are at present in, not being that of vision, we must in many things content ourselves with faith and probability: and in the present question, about the Immateriality of the Soul, if our faculties cannot arrive at demonstrative certainty, we need not think it strange. All the great ends of morality and religion are well enough secured, without philosophical proofs of the soul’s immateriality … since it is evident, that he who made us at the beginning to subsist here, sensible intelligent beings, and for several years continued us in such a state, can and will restore us to the like state of sensibility in another world, and make us capable there to receive the retribution he has designed to men, according to their doings in this life.

And therefore it is not of such mighty necessity to determine one way or the other, as some, over-zealous for or against the immateriality of the soul, have been forward to make the world believe. Who, either on the one side, indulging too much their thoughts immersed altogether in matter, can allow no existence to what is not material: or who, on the other side, finding not cogitation within the natural powers of matter, examined over and over again by the utmost intention of mind, have the confidence to conclude—that Omnipotency itself cannot give perception and thought to a substance which has the modification of solidity. He that considers how hardly sensation is, in our thoughts, reconcilable to extended matter; or existence to anything that has no extension at all, will confess that he is very far from certainly knowing what his soul is. It is a point which seems to me to be put out of the reach of our knowledge: and he who will give himself leave to consider freely, and look into the dark and intricate part of each hypothesis, will scarce find his reason able to determine him fixedly for or against the soul’s materiality. Since, on which side soever he views it, either as an unextended substance , or as a thinking extended matter , the difficulty to conceive either will, whilst either alone is in his thoughts, still drive him to the contrary side. …

It is past controversy, that we have in us something that thinks; our very doubts about what it is, confirm the certainty of its being, though we must content ourselves in the ignorance of what kind of being it is: and it is in vain to go about to be sceptical in this, as it is unreasonable in most other cases to be positive against the being of anything, because we cannot comprehend its nature. For I would fain know what substance exists, that has not something in it which manifestly baffles our understandings …

Can Locke make good on his claim that ‘all the great ends of religion and morality’ can be served, even without a proof of the soul’s immortality? Both religion and morality require, Locke thinks, the certainty of post-mortem rewards and harms. But how can we make sense of the self surviving the death of the body, if we cannot show that the self is immaterial?

(From II.xxvii.8— Idea of identity suited to the idea it is applied to ) It is not therefore unity of substance that comprehends all sorts of identity, or will determine it in every case; but to conceive and judge of it aright, we must consider what idea the word it is applied to stands for: it being one thing to be the same substance , another the same man , and a third the same person , if person , man , and substance , are three names standing for three different ideas;—for such as is the idea belonging to that name, such must be the identity; which, if it had been a little more carefully attended to, would possibly have prevented a great deal of that confusion which often occurs about this matter, with no small seeming difficulties, especially concerning personal identity, which therefore we shall in the next place a little consider.

(From II.xxvii.4) [L]et us suppose an atom, i.e., a continued body under one immutable superficies, existing in a determined time and place; it is evident, that, considered in any instant of its existence, it is in that instant the same with itself. For, being at that instant what it is, and nothing else, it is the same, and so must continue as long as its existence is continued; for so long it will be the same, and no other. In like manner, if two or more atoms be joined together into the same mass, every one of those atoms will be the same, by the foregoing rule: and whilst they exist united together, the mass, consisting of the same atoms, must be the same mass, or the same body, let the parts be ever so differently jumbled. But if one of these atoms be taken away, or one new one added, it is no longer the same mass or the same body. In the state of living creatures, their identity depends not on a mass of the same particles, but on something else. For in them the variation of great parcels of matter alters not the identity: an oak growing from a plant to a great tree, and then lopped, is still the same oak; and a colt grown up to a horse, sometimes fat, sometimes lean, is all the while the same horse: though, in both these cases, there may be a manifest change of the parts; so that truly they are not either of them the same masses of matter, though they be truly one of them the same oak, and the other the same horse. The reason whereof is, that, in these two cases—a mass of matter and a living body —identity is not applied to the same thing.

(From II.xxvii.5– Identity of Vegetables ) We must therefore consider wherein an oak differs from a mass of matter, and that seems to me to be in this, that the one is only the cohesion of particles of matter any how united, the other such a disposition of them as constitutes the parts of an oak; and such an organization of those parts as is fit to receive and distribute nourishment, so as to continue and frame the wood, bark, and leaves, &c., of an oak, in which consists the vegetable life. That being then one plant which has such an organization of parts in one coherent body, partaking of one common life, it continues to be the same plant as long as it partakes of the same life, though that life be communicated to new particles of matter vitally united to the living plant, in a like continued organization conformable to that sort of plants. For this organization, being at any one instant in any one collection of matter, is in that particular concrete distinguished from all other, and is that individual life, which existing constantly from that moment both forwards and backwards, in the same continuity of insensibly succeeding parts united to the living body of the plant, it has that identity which makes the same plant, and all the parts of it, parts of the same plant, during all the time that they exist united in that continued organization, which is fit to convey that common life to all the parts so united.

(From II.xxvii.6– Identity of Animals ) The case is not so much different in brutes but that any one may hence see what makes an animal and continues it the same. Something we have like this in machines, and may serve to illustrate it. For example, what is a watch? it is plain it is nothing but a fit organization or construction of parts to a certain end, which, when a sufficient force is added to it, it is capable to attain. If we would suppose this machine one continued body, all whose organized parts were repaired, increased, or diminished by a constant addition or separation of insensible parts, with one common life, we should have something very much like the body of an animal …

(From II.xxvii.7— The Identity of Man ) This also shows wherein the identity of the same man consists; viz. in nothing but a participation of the same continued life, by constantly fleeting particles of matter, in succession vitally united to the same organized body.

(From II.xxvii.11— Personal Identity ) This being premised, to find wherein personal identity consists, we must consider what person stands for; which, I think, is a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places; which it does only by that consciousness which is inseparable from thinking, and, as it seems to me, essential to it: it being impossible for any one to perceive without perceiving that he does perceive. When we see, hear, smell, taste, feel, meditate, or will anything, we know that we do so. Thus it is always as to our present sensations and perceptions: and by this every one is to himself that which he calls self —it not being considered, in this case, whether the same self be continued in the same or divers substances. For, since consciousness always accompanies thinking, and it is that which makes every one to be what he calls self, and thereby distinguishes himself from all other thinking things, in this alone consists personal identity, i.e., the sameness of a rational being: and as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self now it was then; and it is by the same self with this present one that now reflects on it, that that action was done.

(From II.xxvii.12— Consciousness makes personal Identity ) But it is further inquired, whether it be the same identical substance. This few would think they had reason to doubt of, if these perceptions, with their consciousness, always remained present in the mind, whereby the same thinking thing would be always consciously present, and, as would be thought, evidently the same to itself. But that which seems to make the difficulty is this, that this consciousness being interrupted always by forgetfulness, there being no moment of our lives wherein we have the whole train of all our past actions before our eyes in one view, but even the best memories losing the sight of one part whilst they are viewing another; and we sometimes, and that the greatest part of our lives, not reflecting on our past selves, being intent on our present thoughts, and in sound sleep having no thoughts at all, or at least none with that consciousness which remarks our waking thoughts—I say, in all these cases, our consciousness being interrupted, and we losing the sight of our past selves, doubts are raised whether we are the same thinking thing, i.e., the same substance or no. Which, however reasonable or unreasonable, concerns not personal identity at all. … For as far as any intelligent being can repeat the idea of any past action with the same consciousness it had of it at first, and with the same consciousness it has of any present action; so far it is the same personal self. For it is by the consciousness it has of its present thoughts and actions, that it is self to itself now, and so will be the same self, as far as the same consciousness can extend to actions past or to come; and would be by distance of time, or change of substance, no more two persons, than a man be two men by wearing other clothes to-day than he did yesterday, with a long or a short sleep between: the same consciousness uniting those distant actions into the same person, whatever substances contributed to their production.

(From II.xxvii.14— Personality in Change of Substance ) But the question is, Whether if the same substance which thinks be changed, it can be the same person; or, remaining the same, it can be different persons? And to this I answer: First, This can be no question at all to those who place thought in a purely material animal constitution, void of an immaterial substance. For, whether their supposition be true or no, it is plain they conceive personal identity preserved in something else than identity of substance; as animal identity is preserved in identity of life, and not of substance. And therefore those who place thinking in an immaterial substance only, before they can come to deal with these men, must show why personal identity cannot be preserved in the change of immaterial substances, or variety of particular immaterial substances, as well as animal identity is preserved in the change of material substances, or variety of particular bodies …

(From II.xxvii.15— Whether in Change of thinking Substances there can be one Person ) [I]t must be allowed, that, if the same consciousness (which, as has been shown, is quite a different thing from the same numerical figure or motion in body) can be transferred from one thinking substance to another, it will be possible that two thinking substances may make but one person. For the same consciousness being preserved, whether in the same or different substances, the personal identity is preserved.

(From II.xxvii.17— The body, as well as the soul, goes to the making of a Man ) And thus may we be able, without any difficulty, to conceive the same person at the resurrection, though in a body not exactly in make or parts the same which he had here, the same consciousness going along with the soul that inhabits it. But yet the soul alone, in the change of bodies, would scarce to any one but to him that makes the soul the man, be enough to make the same man. For should the soul of a prince, carrying with it the consciousness of the prince’s past life, enter and inform the body of a cobbler, as soon as deserted by his own soul, every one sees he would be the same person with the prince, accountable only for the prince’s actions: but who would say it was the same man ?

(From II.xxvii.19— Self depends on Consciousness, not on Substance ) Self is that conscious thinking thing—whatever substance made up of (whether spiritual or material, simple or compounded, it matters not)—which is sensible or conscious of pleasure and pain, capable of happiness or misery, and so is concerned for itself, as far as that consciousness extends.

(From II.xxvii.20— Persons, not Substances, the Objects of Reward and Punishment ) In this personal identity is founded all the right and justice of reward and punishment; happiness and misery being that for which every one is concerned for himself , and not mattering what becomes of any substance , not joined to, or affected with that consciousness.

(From II.xxvii.21— Which shows wherein Personal identity consists ) This may show us wherein personal identity consists: not in the identity of substance, but, as I have said, in the identity of consciousness … if Socrates waking and sleeping do not partake of the same consciousness, Socrates waking and sleeping is not the same person. And to punish Socrates waking for what sleeping Socrates thought, and waking Socrates was never conscious of, would be no more of right, than to punish one twin for what his brother-twin did, whereof he knew nothing, because their outsides were so like, that they could not be distinguished; for such twins have been seen.

(From II.xxvii.24— Objection ) But is not a man drunk and sober the same person? Why else is he punished for the fact he commits when drunk, though he be never afterwards conscious of it? Just as much the same person as a man that walks, and does other things in his sleep, is the same person, and is answerable for any mischief he shall do in it. Human laws punish both, with a justice suitable to their way of knowledge; because, in these cases, they cannot distinguish certainly what is real, what counterfeit: and so the ignorance in drunkenness or sleep is not admitted as a plea. But in the great day, wherein the secrets of all hearts shall be laid open, it may be reasonable to think, no one shall be made to answer for what he knows nothing of; but shall receive his doom, his conscience accusing or excusing him.

• What is Locke’s sortal relativity thesis?
• Atom over time?
• Mass of atoms?
• What does Descartes think accounts for personal identity over time?
• What does Locke think is wrong with Descartes’s answer?

It now makes sense to turn to Locke’s official discussion of the limits of knowledge. Keep in mind that the two orders of classification Locke introduces (manners or degrees of knowledge and the objects known) cut across each other. I’ve chosen to frame the discussion in terms of the objects of knowledge: identity (known by intuition), relation (by demonstration), co-existence, and real existence (by sensation).

(From IV.i.1— Our Knowledge conversant about our Ideas only ) Since the mind, in all its thoughts and reasonings, hath no other immediate object but its own ideas, which it alone does or can contemplate, it is evident that our knowledge is only conversant about them.

(From IV.i.2— Knowledge is the perception of the agreement or disagreement of two ideas ) Knowledge then seems to me to be nothing but the perception of the connexion of and agreement, or disagreement and repugnancy of any of our ideas . In this alone it consists. Where this perception is, there is knowledge, and where it is not, there, though we may fancy, guess, or believe, yet we always come short of knowledge. For when we know that white is not black, what do we else but perceive, that these two ideas do not agree? when we possess ourselves with the utmost security of the demonstration, that the three angles of a triangle are equal to two right ones, what do we more but perceive, that equality to two right ones does necessarily agree to, and is inseparable from, the three angles of a triangle?

(From IV.i.3— This Agreement or Disagreement may be any of four sorts ) But to understand a little more distinctly wherein this agreement or disagreement consists, I think we may reduce it all to these four sorts: i. identity , or diversity . ii. relation . iii. co-existence , or necessary connexion . iv. real existence .

(From IV.i.4— First, of Identity, or Diversity in ideas ) First , as to the first sort of agreement or disagreement, viz. identity or diversity . It is the first act of the mind, when it has any sentiments or ideas at all, to perceive its ideas; and so far as it perceives them, to know each what it is, and thereby also to perceive their difference, and that one is not another.

(From IV.i.5— Secondly, of abstract Relations between ideas ) Secondly , the next sort of agreement or disagreement the mind perceives in any of its ideas may, I think, be called relative , and is nothing but the perception of the relation between any two ideas, of what kind soever, whether substances, modes, or any other.

(From IV.i.6— Thirdly, of their necessary Co-existence in Substances ) The third sort of agreement or disagreement to be found in our ideas, which the perception of the mind is employed about, is co-existence or non-co-existence in the same subject ; and this belongs particularly to substances. Thus when we pronounce concerning gold, that it is fixed, our knowledge of this truth amounts to no more but this, that fixedness, or a power to remain in the fire unconsumed, is an idea that always accompanies and is joined with that particular sort of yellowness, weight, fusibility, malleableness, and solubility in aqua regia , which make our complex idea signified by the word ‘gold’.

(From IV.iii.9– Of their Co-existence, extends only a very little way ) [A]s to the … agreement or disagreement of our ideas in co-existence , in this our knowledge is very short; though in this consists the greatest and most material part of our knowledge concerning substances. For our ideas of the species of substances being, as I have showed, nothing but certain collections of simple ideas united in one subject, and so co-existing together; e.g., our idea of flame is a body hot, luminous, and moving upward; of gold, a body heavy to a certain degree, yellow, malleable, and fusible: for these, or some such complex ideas as these, in men’s minds, do these two names of the different substances, flame and gold, stand for. When we would know anything further concerning these, or any other sort of substances, what do we inquire, but what other qualities or powers these substances have or have not? which is nothing else but to know what other simple ideas do, or do not co-exist with those that make up that complex idea?

(From IV.iii.10— Because the Connexion between simple Ideas in substances is for the most part unknown ) This, how weighty and considerable a part soever of human science, is yet very narrow, and scarce any at all. The reason whereof is, that the simple ideas whereof our complex ideas of substances are made up are, for the most part, such as carry with them, in their own nature, no visible necessary connexion or inconsistency with any other simple ideas, whose co-existence with them we would inform ourselves about.

(From IV.iii.25) If a great, nay, far the greatest part of the several ranks of bodies in the universe escape our notice by their remoteness, there are others that are no less concealed from us by their minuteness. These insensible corpuscles , being the active parts of matter, and the great instruments of nature, on which depend not only all their secondary qualities, but also most of their natural operations, our want of precise distinct ideas of their primary qualities keeps us in an incurable ignorance of what we desire to know about them.

I doubt not but if we could discover the figure, size, texture, and motion of the minute constituent parts of any two bodies, we should know without trial several of their operations one upon another; as we do now the properties of a square or a triangle. Did we know the mechanical affections of the particles of rhubarb, hemlock, opium, and a man, as a watchmaker does those of a watch, whereby it performs its operations; and of a file, which by rubbing on them will alter the figure of any of the wheels; we should be able to tell beforehand that rhubarb will purge, hemlock kill, and opium make a man sleep: as well as a watchmaker can, that a little piece of paper laid on the balance will keep the watch from going till it be removed; or that, some small part of it being rubbed by a file, the machine would quite lose its motion, and the watch go no more. The dissolving of silver in aqua fortis , and gold in aqua regia , and not vice versa , would be then perhaps no more difficult to know than it is to a smith to understand why the turning of one key will open a lock, and not the turning of another. But whilst we are destitute of senses acute enough to discover the minute particles of bodies, and to give us ideas of their mechanical affections, we must be content to be ignorant of their properties and ways of operation; nor can we be assured about them any further than some few trials we make are able to reach. But whether they will succeed again another time, we cannot be certain. This hinders our certain knowledge of universal truths concerning natural bodies: and our reason carries us herein very little beyond particular matter of fact.

(From IV.vi.9— No discoverable necessary connexion between nominal essence gold, and other simple ideas ) As there is no discoverable connexion between fixedness and the colour, weight, and other simple ideas of that nominal essence of gold; so, if we make our complex idea of gold, a body yellow, fusable, ductile, weighty, and fixed, we shall be at the same uncertainty concerning solubility in aqua regia , and for the same reason. Since we can never, from consideration of the ideas themselves, with certainty affirm or deny of a body whose complex idea is made up of yellow, very weighty, ductile, fusible, and fixed, that it is soluble in aqua regia : and so on of the rest of its qualities. I would gladly meet with one general affirmation concerning any will, no doubt, be presently objected, is not this an universal proposition, “all gold is malleable” ? to which I answer, it is a very complex idea the word ‘gold’ stands for. But then here is nothing affirmed of gold, but that that sound stands for an idea in which malleableness is contained: and such a sort of truth and certainty as this it is, to say a centaur is four-footed. But if malleableness make not a part of the specific essence the name of ‘gold’ stands for, it is plain, “all gold is malleable” , is not a certain proposition. Because, let the complex idea of gold be made up of whichsoever of its other qualities you please, malleableness will not appear to depend on that complex idea, nor follow from any simple one contained in it: the connexion that malleableness has (if it has any) with those other qualities being only by the intervention of the real constitution of its insensible parts; which, since we know not, it is impossible we should perceive that connexion, unless we could discover that which ties them together.

(From IV.i.7— Fourthly, of real Existence agreeing to any idea ) The fourth and last sort is that of actual real existence agreeing to any idea.

(From IV.ii.1— Of the degrees, or differences in clearness, of our Knowledge )

• Intuitive: The different clearness of our knowledge seems to me to lie in the different way of perception the mind has of the agreement or disagreement of any of its ideas. For if we will reflect on our own ways of thinking, we will find, that sometimes the mind perceives the agreement or disagreement of two ideas immediately by themselves , without the intervention of any other: and this I think we may call intuitive knowledge .

(From IV.ii.2)

• Demonstrative: The next degree of knowledge is, where the mind perceives the agreement or disagreement of any ideas, but not immediately. Though wherever the mind perceives the agreement or disagreement of any of its ideas, there be certain knowledge; yet it does not always happen, that the mind sees that agreement or disagreement, which there is between them, even where it is discoverable; and in that case remains in ignorance, and at most gets no further than a probable conjecture. … In this case then, when the mind cannot so bring its ideas together as by their immediate comparison, and as it were juxta-position or application one to another, to perceive their agreement or disagreement, it is fain, by the intervention of other ideas , (one or more, as it happens) to discover the agreement or disagreement which it searches; and this is that which we call reasoning . …

(From IV.ii.14)

• Sensitive knowledge of the particular existence of finite beings without us. These two, viz. intuition and demonstration, are the degrees of our knowledge ; whatever comes short of one of these, with what assurance soever embraced, is but faith or opinion , but not knowledge, at least in all general truths. There is, indeed, another perception of the mind, employed about the particular existence of finite beings without us, which, going beyond bare probability, and yet not reaching perfectly to either of the foregoing degrees of certainty, passes under the name of knowledge . There can be nothing more certain than that the idea we receive from an external object is in our minds: this is intuitive knowledge. But whether there be anything more than barely that idea in our minds; whether we can thence certainly infer the existence of anything without us, which corresponds to that idea, is that whereof some men think there may be a question made; because men may have such ideas in their minds, when no such thing exists, no such object affects their senses. But yet here I think we are provided with an evidence that puts us past doubting. For I ask any one, whether he be not invincibly conscious to himself of a different perception, when he looks on the sun by day, and thinks on it by night; when he actually tastes wormwood, or smells a rose, or only thinks on that savour or odour? We as plainly find the difference there is between any idea revived in our minds by our own memory, and actually coming into our minds by our senses, as we do between any two distinct ideas. If any one say, a dream may do the same thing, and all these ideas may be produced, in us without any external objects; he may please to dream that I make him this answer:

That it is no great matter, whether I remove his scruple or no: where all is but dream, reasoning and arguments are of no use, truth and knowledge nothing. That I believe he will allow a very manifest difference between dreaming of being in the fire, and being actually in it. But yet if he be resolved to appear so sceptical as to maintain, that what I call being actually in the fire is nothing but a dream; and that we cannot thereby certainly know, that any such thing as fire actually exists without us: I answer, that we certainly finding that pleasure or pain follows upon the application of certain objects to us, whose existence we perceive, or dream that we perceive, by our senses; this certainty is as great as our happiness or misery, beyond which we have no concernment to know or to be. So that, I think, we may add to the two former sorts of knowledge this also, of the existence of particular external objects, by that perception and consciousness we have of the actual entrance of ideas from them, and allow these three degrees of knowledge, viz. intuitive , demonstrative , and sensitive ; in each of which there are different degrees and ways of evidence and certainty.

(From IV.iv.1— Objection: “Knowledge placed in our ideas may be all unreal or chimerical” ) I doubt not but my reader, by this time, may be apt to think that I have been all this while only building a castle in the air; and be ready to say to me: To what purpose all this stir? knowledge, say you, is only the perception of the agreement or disagreement of our own ideas: but who knows what those ideas may be? Is there anything so extravagant as the imaginations of men’s brains? where is the head that has no chimeras in it? … If it be true, that all knowledge lies only in the perception of the agreement or disagreement of our own ideas, the visions of an enthusiast and the reasonings of a sober man will be equally certain.

(From IV.iv.2— Answer Not so, where Ideas agree with Things ) To which I answer, That if our knowledge of our ideas terminate in them, and reach no further, where there is something further intended, our most serious thoughts will be of little more use than the reveries of a crazy brain. … But I hope, before I have done, to make it evident, that this way of certainty, by the knowledge of our own ideas, goes a little further than bare imagination: and I believe it will appear that all the certainty of general truths a man has lies in nothing else.

(From IV.iv.3— But what shall be the criterion of this agreement? ) It is evident the mind knows not things immediately, but only by the intervention of the ideas it has of them. Our knowledge, therefore, is real only so far as there is a conformity between our ideas and the reality of things. But what shall be here the criterion? How shall the mind, when it perceives nothing but its own ideas, know that they agree with things themselves? this, though it seems not to want difficulty, yet, I think, there be two sorts of ideas that we may be assured agree with things.

(From IV.iv.4— As, first all simple ideas are really conformed to things ) First , the first are simple ideas, which since the mind, as has been showed, can by no means make to itself, must necessarily be the product of things operating on the mind, in a natural way, and producing therein those perceptions which by the Wisdom and Will of our Maker they are ordained and adapted to. From whence it follows, that simple ideas are not fictions of our fancies, but the natural and regular productions of things without us, really operating upon us; and so carry with them all the conformity which is intended; or which our state requires: for they represent to us things under those appearances which they are fitted to produce in us: whereby we are enabled to distinguish the sorts of particular substances, to discern the states they are in, and so to take them for our necessities, and apply them to our uses. Thus the idea of whiteness, or bitterness, as it is in the mind, exactly answering that power which is in any body to produce it there, has all the real conformity it can or ought to have, with things without us. And this conformity between our simple ideas and the existence of things, is sufficient for real knowledge.

• What is the difference between knowledge and ‘real’ knowledge?
• How can we know whether we have ‘real’ knowledge or not?

Scholars disagree on just how Locke means to respond to skepticism. But it certainly looks as if he is invoking God at some crucial points in his defense of the reality of knowledge. What follows is Locke’s sketch of his argument for God’s existence; the details are to be found later in IV.x.

(From IV.x.1— We are capable of knowing certainly that there is a God ) Though God has given us no innate ideas of himself; though he has stamped no original characters on our minds, wherein we may read his being; yet having furnished us with those faculties our minds are endowed with, he hath not left himself without witness …

(From IV.x.2— For Man knows that he himself exists ) I think it is beyond question, that man has a clear idea of his own being; he knows certainly he exists, and that he is something. He that can doubt whether he be anything or no, I speak not to … This, then, I think I may take for a truth, which every one’s certain knowledge assures him of, beyond the liberty of doubting, viz. that he is something that actually exists .

(From IV.x.3— He knows also that Nothing cannot produce a Being; therefore something must have existed from Eternity ) In the next place, man knows, by an intuitive certainty, that bare nothing can no more produce any real being, than it can be equal to two right angles . [I]t is [thus] an evident demonstration, that from eternity there has been something ; since what was not from eternity had a beginning; and what had a beginning must be produced by something else.

(From IV.x.4— And that eternal being must be most powerful ) Next, it is evident, that what had its being and beginning from another, must also have all that which is in and belongs to its being from another too. All the powers it has must be owing to and received from the same source. This eternal source, then, of all being must also be the source and original of all power; and so this eternal being must be also the most powerful .

(From IV.x.5— And most knowing ) Again, a man finds in himself perception and knowledge. We have then got one step further; and we are certain now that there is not only some being, but some knowing, intelligent being in the world. There was a time, then, when there was no knowing being, and when knowledge began to be; or else there has been also a knowing being from eternity . If it be said, there was a time when no being had any knowledge, when that eternal being was void of all understanding; I reply, that then it was impossible there should ever have been any knowledge: it being as impossible that things wholly void of knowledge, and operating blindly, and without any perception, should produce a knowing being, as it is impossible that a triangle should make itself three angles bigger than two right ones. For it is as repugnant to the idea of senseless matter, that it should put into itself sense, perception, and knowledge, as it is repugnant to the idea of a triangle, that it should put into itself greater angles than two right ones.

(From IV.x.6— And therefore God ) Thus, from the consideration of ourselves, and what we infallibly find in our own constitutions, our reason leads us to the knowledge of this certain and evident truth— that there is an eternal, most powerful, and most knowing being ; which whether any one will please to call God, it matters not.

• Locke’s argument for God’s existence, as presented in these passages, looks pretty weak. What’s wrong with it?

Modern Philosophy Copyright © 2013 by Walter Ott and Alex Dunn is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Part of: The Works of John Locke in Nine Volumes The Works, vol. 1 An Essay concerning Human Understanding Part 1

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The first part of Locke’s most important work of philosophy. Continued in volume 2.

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Peaden offers a feminist reading of Essay Concerning Human Understanding, and discusses how it planted seeds for modern feminism(s) while also examining how it reified a discursive system which has been used to oppress women.

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Selected Works of John Locke

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An Essay Concerning Human Understanding

NOTE: This is a single-section Summary & Analysis of Essay Concering Human Understanding . SparkNotes also offers a full-length study guide of with 16 sections of Summary & Analysis and other useful features  here .

John Locke’s  Essay Concering Human Understanding  presents a detailed, systematic philosophy of mind and thought. The  Essay  wrestles with fundamental questions about how we think and perceive, and it even touches on how we express ourselves through language, logic, and religious practices. In the introduction, entitled   The Epistle to the Reader,  Locke describes how he became involved in his current mode of philosophical thinking. He relates an anecdote about a conversation with friends that made him realize that men often suffer in their pursuit of knowledge because they fail to determine the limits of their understanding.

Summary: Book 1

In Book 1, Locke lays out the three goals of his philosophical project: to discover where our ideas come from, to ascertain what it means to have these ideas and what an idea essentially is, and to examine issues of faith and opinion to determine how we should proceed logically when our knowledge is limited. Locke attacks previous schools of philosophy, such as those of Plato and Descartes, that maintain a belief in a priori , or innate, knowledge. He begins by opposing the idea that we are all born knowing certain fundamental principles, such as “whatever is, is.” The usual justification for this belief in innate principles is that certain principles exist to which all human beings universally assent. Locke contends that, on the contrary, no principle is actually accepted by every human being. Furthermore, if universal agreement did exist about something, this agreement might have come about in a way other than through innate knowledge.

Locke offers another argument against innate knowledge, asserting that human beings cannot have ideas in their minds of which they are not aware, so that people cannot be said to possess even the most basic principles until they are taught them or think them through for themselves. Still another argument is that because human beings differ greatly in their moral ideas, moral knowledge must not be innate. Finally, Locke confronts the theory of innate ideas (along the lines of the Platonic Theory of Forms) and argues that ideas often cited as innate are so complex and confusing that much schooling and thought are required to grasp their meaning. Against the claim that God is an innate idea, Locke counters that God is not a universally accepted idea and that his existence cannot therefore be innate human knowledge.

Summary: Book 2

Having eliminated the possibility of innate knowledge, Locke in Book 2 seeks to demonstrate where knowledge comes from. He proposes that knowledge is built up from ideas, either simple or complex. Simple ideas combine in various ways to form complex ideas. Therefore, the most basic units of knowledge are simple ideas, which come exclusively through experience. There are two types of experience that allow a simple idea to form in the human mind: sensation, or when the mind experiences the world outside the body through the five senses, and reflection, or when the mind turns inward, recognizing ideas about its own functions, such as thinking, willing, believing, and doubting. Locke divides simple ideas into four categories:

(1) ideas we get from a single sense, such as sight or taste;

(2) ideas created from more than one sense, such as shape and size;

(3) ideas emerging from reflection; and

(4) ideas arising from a combination of sensation and reflection, such as unity, existence, pleasure, pain, and substance.

Locke goes on to explain the difference between primary and secondary qualities. Ideas of primary qualities—such as texture, number, size, shape, and motion—resemble their causes. Ideas of secondary qualities do not resemble their causes, as is the case with color, sound, taste, and odor. In other words, primary qualities cannot be separated from the matter, whereas secondary qualities are only the power of an object to produce the idea of that quality in our minds.

Locke devotes much of Book 2 to exploring various things that our minds are capable of, including making judgments about our own perceptions to refine our ideas, remembering ideas, discerning between ideas, comparing ideas to one another, composing a complex idea from two or more simple ideas, enlarging a simple idea into a complex idea by repetition, and abstracting certain simple ideas from an already complex ideas.

Locke also discusses complex ideas, breaking them down into four basic types:

(1) modes, which are ideas that do not exist in and of themselves, such as qualities, numbers, and other abstract concepts;

(2) substances, either self-subsisting things (such as a particular man or a sheep) or collections of such things (an army of men or a flock of sheep);

(3) relations, such as  father , bigger , and morally good ; and

(4) abstract generals, such as “man” or “sheep” in general.

Complex ideas are created through three methods: combination, comparison, and abstraction.

Summary: Book 3

In Book 3, Locke discusses abstract general ideas. Everything that exists in the world is a particular “thing.” General ideas occur when we group similar particular ideas and take away, or abstract, the differences until we are left only with the similarities. We then use these similarities to create a general term, such as “tree,” which is also a general idea. We form abstract general ideas for three reasons: it would be too hard to remember a different word for every particular thing that exists, having a different word for everything that exists would obstruct communication, and the goal of science is to generalize and categorize everything.

Locke argues against the notion of essences , a concept that had been widely accepted since at least Plato’s time. Plato argued that we can only recognize individuals as members of a species because we are aware of the essence of that species—for example, we recognize a particular tree as a tree because we understand what a tree is in its essence. Locke argues that essences don’t actually exist as ideal entities but are instead nothing more than the abstract, general ideas that we form about the things we observe, things that actually exist in the world. Human beings decide which differences and similarities they will use to separate and classify particular things into categories—they choose how to define categories rather than discovering the essence of a given species.

Despite having just criticized the traditional concept of essences, Locke decides to adopt the term into his own philosophy and proceeds to distinguish between real essences and nominal essences. Nominal essences are the specific collections of observable properties from which we create an abstract general idea. For example, we observe similarities between many different individual dogs and from these observations form our idea of what a dog is. Real essences are the invisible structures and arrangements of corpuscles or atoms that allow for those observable properties to be observable in the first place. For example, to return to the case of dogs, if we could fully understand the biological structures and processes that make a dog a dog, whether those would include DNA or other things as well, then we would understand the real essence of dogs. Unlike the nominal essence, the real essence has a basis in reality.

Locke moves on to discuss language, pointing out natural weaknesses and common abuses of language. The most significant problem with words is that they do not immediately and obviously mean the same thing to all people. This problem has four main causes:

(1) a word may imply a very complex idea,

(2) the ideas that words stand for may have no constant standard anywhere in nature to judge them against,

(3) the standard that ideas refer to may not be easily known, and

(4) the meaning of a word and the real nature of the thing referred to by the word may not be exactly the same.

Locke also identifies six common abuses:

(1) people often use words without really knowing what these words mean,

(2) people use words inconsistently,

(3) people purposefully make terms obscure by using old words for new and unusual uses or by introducing new terms without defining them,

(4) people mistakenly believe that words refer to things rather than ideas,

(5) people try to use words incorrectly to change their meaning, and

(6) people assume that others know what they are saying when they are not really being clear.

Locke suggests four remedies to counteract the natural shortcomings and the abuses of language:

(1) never use a word without having a clear idea of what it means;

(2) try to recognize the same meaning for words as others do so that we can communicate with a common vocabulary;

(3) if there is the slightest chance that the meaning of your words will be unclear, define your terms; and

(4) always use words consistently.

Summary: Book 4

In Book 4, Locke addresses the nature of knowledge itself, asking what knowledge is and in what areas we can hope to attain it. For Locke, knowledge is what the mind is able to perceive through reasoning out the connection, or lack of connection, between any two or more of our ideas. Because knowledge only has to do with relations between ideas, which are in the mind, the knowledge we are capable of is not actually knowledge of the world itself. Locke identifies four sorts of agreement and disagreement that reason can perceive to produce knowledge:

(1) identity (blue is blue) and diversity (blue is not yellow),

(2) relation (two triangles with equal bases located between the same two parallel lines are equal triangles),

(3) coexistence (iron is always susceptible to magnets), and

(4) realization that existence belongs to the ideas themselves and is not in the mind (the idea of God and of the self).

Locke distinguishes between three grades or degrees of knowledge: intuition, when we immediately perceive an agreement or disagreement the moment the ideas are understood; demonstration, which requires some sort of proof; and sensitive knowledge, which is about the existence of an external world, roughly resembling the world as we perceive it.

Locke argues that we can never really develop a system of knowledge in natural philosophy. The best that we can do is to observe certain qualities in the world that tend to occur together on a regular basis. The kind of connection he demands is the sort that we find between properties occurring together regularly in geometrical figures. Although he doesn’t seem to think we will ever be able to know more about the true nature of things, Locke is hopeful that we can understand existence, and the properties of things that exist in the world, much more thoroughly.

Locke outlines three strategies for dealing with the problem of skepticism, or doubt about whether the world exists outside of our minds. This problem arises naturally from Locke’s theory of knowledge. If we only have access to the ideas in our minds, which only exist in our minds, how do we know there is a real world outside of our minds? Locke’s first strategy is to refuse to take the skeptic seriously. Can anyone really doubt, he asks, that there is an external world out there? His second strategy is to say that it doesn’t matter whether we doubt the existence of an outside world or not. All that matters is that we know enough to enable us to get around in the world.

His third line of attack involves seven marks of our experience that can best be explained by the existence of an external world:

(1) there is a certain realness and strength of clarity to perception of an immediate object that memories or products of the imagination do not have,

(2) we cannot get these ideas without the sense organ appropriate to them,

(3) we are able to receive ideas of this sort only in certain situations so it cannot be the organs themselves that are responsible for producing the ideas,

(4) we receive ideas passively,

(5) some ideas are accompanied by pleasure or pain but the memories of those ideas are not,

(6) our senses often bear witness to the truth of each other’s reports, and

(7) two different people can share the same experience.

Locke argues that almost all of science, with the exception of mathematics and morality, and most of our everyday experience is subject to opinion or judgment. We base our judgments on the similarity between propositions to our own experience and to the experiences we have heard described by others. Locke examines the relation between reason and faith. He defines reason as being the faculty we use to obtain judgment and knowledge. Faith is the acceptance of revelation and has its own truths, which reason cannot discover. Reason, however, must always be used to determine which revelations truly are revelations from God and which are the constructions of man. Finally, Locke divides all of human understanding into three sciences: natural philosophy, or the study of things to gain knowledge; ethics, or the study of how it is best to act; and logic, or the study of words and signs.

Analysis: Locke’s  Essay Concering Human Understanding

Locke effectively shifted the focus of 17th-century philosophy from metaphysics to the more basic problems of epistemology, or how people are able to acquire knowledge and understanding. Locke rigorously addresses many different aspects of human understanding and of the mind’s functions. His most striking innovation in this regard is his rejection of the theory that human beings are born possessing innate knowledge, which philosophers such as Plato and Descartes had sought to prove.

Locke replaces the theory of innate knowledge with his own signature concept, the tabula rasa , or blank slate. Locke tries to demonstrate that we are born with no knowledge whatsoever—we are all blank slates at birth—and that we can only know that things exist if we first experience them.

Locke builds a strong case against the existence of innate knowledge, but the model of knowledge he proposes in its place is not without flaws. By emphasizing the necessity of experience as a prerequisite for knowledge, Locke downplays the role of the mind and neglects to adequately address how knowledge exists and is retained in the mind—in other words, how we remember knowledge and what happens to our knowledge when we aren’t thinking about it and it is temporarily out of our consciousness. While Locke is thorough in his discussion of what objects of experience can be known, he leaves us with little idea of how the mind works to translate experiences into knowledge and to combine certain experiences with other bits of knowledge to categorize and interpret future information.

Locke presents “simple” ideas as a basic unit of human understanding, claiming that we can break all of our experiences down into these simple, fundamental parts that cannot be broken down any further. For example, the idea of a plain wooden chair can be broken down into simpler units that are received by our minds through one sense, through multiple senses, through reflection, or through a combination of sensation and reflection. “Chair” is thus perceived and understood by us in several ways: as brown, as hard, as according to its function (to be sat upon), and as a certain shape that is unique to the object “chair.” These simple ideas allow us to understand what “chair” is and to recognize it when we come in contact with it.

Locke’s theory of primary and secondary qualities is based on the Corpuscular Hypothesis of Robert Boyle, Locke’s friend and contemporary. According to the Corpuscular Hypothesis, which Locke considered the best scientific picture of the world in his day, all matter is composed of tiny particles, or corpuscles, which are too small to see individually and which are colorless, tasteless, soundless, and odorless. The arrangement of these invisible particles of matter gives an object of perception both its primary and secondary qualities. An object’s primary qualities include its size, shape, and movement. They are primary in the sense that these qualities exist regardless of whether anyone perceives them. Secondary qualities include color, odor, and taste, and they are secondary in the sense that they may be perceived by observers of the object, but they are not inherent in the object. For example, a rose’s shape and the way it grows are primary because they exist regardless of whether they are observed, but the rose’s redness only exists for an observer under the right conditions of lighting and if the observer’s eyesight is functioning normally. Locke suggests that because we can explain everything using the existence only of corpuscles and primary qualities, we have no reason to think that secondary qualities have any real basis in the world.

According to Locke, every idea is an object of some action of perception and thinking. An idea is an immediate object of our thoughts, something we perceive and to which we are actively paying attention. We also perceive some things without ever thinking about them, and these things do not continue to exist in our minds because we have no reason to think about them or remember them. The latter are nonimmediate objects. When we perceive an object’s secondary qualities, we are actually perceiving something that does not exist outside of our minds. In each of these cases, Locke would maintain that the act of perception always has an internal object—the thing that is perceived exists in our mind. Moreover, the object of perception sometimes exists only  in our minds. One of the more confusing aspects of Locke’s discussion is the fact that perception and thinking are sometimes, but not always, the same action. To add to the confusion, Locke claims in Book II that an action of perception may  have a nonimmediate object, not that it must have one . This makes it difficult to pin down a rule for what perception is and isn’t, and how perception works.

We may find Locke’s discussion of essence, or substance, confusing because Locke himself doesn’t seem convinced of its existence. Locke may have chosen to retain this concept for several possible reasons. First, he seems to think that the idea of essence is necessary to make sense of our language. Second, the concept of essence solves the problem of persistence through change: that is, if a tree is just a bundle of ideas such as “tall,” “green,” “leaves,” and so on, what happens when a tree is short and leafless? Does this new collection of qualities change the essence from “tree” to something new? In Locke’s view, the essence persists through any change, remaining the same despite changes in the object’s properties. A third reason Locke seem to be compelled to accept the notion of essence is to explain what unifies ideas that occur at the same time, making them into a single thing, distinct from any other thing. Essence helps clarify this unity, though Locke is not very specific about how this works. For Locke, essence is what qualities are dependent on and exist in.

Locke’s view that our knowledge is much more limited than was previously supposed was shared by other seventeenth-and eighteenth-century thinkers such as Descartes and Hume—even though Locke differs sharply from Descartes about why that knowledge is limited. For Locke, however, the fact that our knowledge is limited is a philosophical rather than practical matter. Locke points out that the very fact that we do not take such skeptical doubts about the existence of the external world seriously is a sign of how overwhelmingly probable we feel the existence of the world to be. The overwhelming clarity of the idea of an external world, and the fact that it is confirmed by everybody except madmen, is important to Locke in and of itself. Even so, Locke holds that we can never have real knowledge when it comes to natural science. Rather than encouraging us to stop bothering with science, Locke seems to say instead that we should be aware of its limitations.

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An essay concerning humane understanding. In four books.

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