An Essay Concerning Human Understanding

Summary

Locke says in the Epistle to the Reader that the Essay began when five or six friends meeting in his rooms found themselves at a standstill over questions of morality and revealed religion, and he proposed that they first examine what objects human understanding is fitted to deal with. Nearly twenty years later the result was a long, patient survey of where ideas come from, how they combine, how words signify them and how far knowledge and probable belief can reach. Book I attacks the doctrine of innate principles. If any speculative or practical truths were stamped on the mind, children, 'idiots' and whole nations would assent to them, yet none commands universal assent, and even the idea of God differs widely between peoples. Book II, the longest and most influential, supposes the mind to be white paper and derives every idea from two sources: sensation of external objects and reflection on the mind's own operations. Simple ideas are passively received; the mind actively compounds, compares and abstracts them into complex ideas of modes, substances and relations. Along the way Locke distinguishes primary qualities such as solidity, extension and figure, which resemble their ideas, from secondary qualities such as colour, taste and warmth, which are only powers in bodies to produce sensations. He reports William Molyneux's question whether a man born blind and newly sighted could tell a globe from a cube by sight alone, and agrees that he could not. He explains madness as right reasoning from wrongly joined ideas, analyses power and the will at great length, and concedes that our idea of substance is only a supposed something we know not what. The chapter on identity, added in 1694, separates the identity of a man, a living organism, from the identity of a person, which extends exactly as far as consciousness reaches back, with thought experiments about a prince's soul in a cobbler's body and a waking and sleeping Socrates. The final chapter of Book II, added in the fourth edition, names the association of ideas and treats chance connexions made by custom as a kind of madness found in nearly everyone. Book III examines language: words stand for ideas in the speaker's mind, general terms name abstract ideas, and the 'real essences' of natural kinds are unknown, so much dispute is merely verbal. Book IV defines knowledge as the perception of agreement or disagreement between ideas, ranks intuition, demonstration and sensitive knowledge, and admits that most of life runs on probability, judgment and faith regulated by reason, closing with a warning against religious enthusiasm.

Plot or Argument

• Epistle and Introduction: measuring the understanding

  Locke presents himself as an under-labourer clearing rubbish for scientists like Boyle, Sydenham, Huygens and Newton. The aim is to learn the extent of our faculties so that we neither despair of knowledge nor dispute about what lies beyond it.

• Book I: Against innate principles

  Neither speculative maxims (whatever is, is) nor moral rules nor the idea of God are universally assented to; children and the uneducated lack them, and moral rules vary across societies. Supposed innate principles are early-learned opinions.

• Book II, Ch. I–XI: Simple ideas and the operations of the mind

  All ideas arise from sensation and reflection. Locke treats solidity, primary and secondary qualities, perception (including Molyneux's problem), retention, discerning and composition, and distinguishes madmen, who join ideas wrongly, from naturals, who lack quickness.

• Book II, Ch. XII–XXI: Modes, infinity, pleasure and power

  Complex ideas of space, duration, number and infinity are built from simple ones. The very long chapter on power analyses volition, argues that the will is determined by present uneasiness, and explains how a drunkard can see his ruin and still drink.

• Book II, Ch. XXIII: Substance as 'something we know not what'

  Our ideas of particular substances are collections of qualities with an unknown support. The idea of spiritual substance is as clear, or as obscure, as that of material substance.

• Book II, Ch. XXVII: Identity of man and of person

  Identity depends on the kind of thing: an organism persists through continuous life; a person, a forensic term for an agent who can be held accountable, persists as far as consciousness extends. Locke tests the view on memory loss, drunkenness, sleepwalking and soul transfer.

• Book II, Ch. XXXIII: The association of ideas

  Ideas united by chance or custom rather than nature produce antipathies, phobias and prejudice. Locke's cases include a man cured of madness who could never bear to see his operator, a mother's unending grief and a dancer who needed a trunk in the room.

• Book III: Words and essences

  Words signify ideas, not things directly. General terms name abstract ideas made by the mind; the real essences of gold or a horse are unknown, and the imperfection and abuse of words cause many disputes.

• Book IV: Knowledge, probability, faith and enthusiasm

  Knowledge is perception of agreement between ideas, by intuition, demonstration or sensation of existing things. Beyond it lies probability. Faith is assent to revelation that reason must still judge; enthusiasm, trusting private inner light without reason, is condemned.

Characters

• William Molyneux, correspondent

  Dublin scientist whose letter posed the problem of whether a newly sighted blind man could recognise a globe and cube by sight; Locke inserted it in the second edition.

• The prince and the cobbler, thought experiment

  A prince's soul, carrying his memories, enters a cobbler's body: the same person as the prince, Locke says, but not the same man.

• Socrates waking and sleeping, thought experiment

  If waking and sleeping Socrates did not share consciousness, they would be different persons, and one should not be punished for the other's thoughts.

• The young gentleman who learned to dance, case of association

  Could dance well only when an old trunk stood in the room as it had during his lessons; Locke vouches for the story's source.

• The man cured of madness, case of association

  Recovered by a harsh and painful operation, he was grateful for life but could never bear the sight of the operator.

Lessons

• Experience writes on a mind that begins blank

  Locke denies that any principles are inborn and traces every idea to sensation or reflection. The practical upshot is that education, environment and early impressions shape minds profoundly, for good or ill.

  • Is the 'white paper' image consistent with Locke's admission that the mind has active powers?
  • What would Locke make of modern evidence for innate perceptual and linguistic capacities?
  • Why does Locke think belief in innate principles serves people who want authority over others' opinions?

• A person reaches as far as memory and consciousness reach

  Locke separates the human organism from the person, an accountable self constituted by consciousness of past actions. This makes identity a question of psychological continuity, with direct consequences for punishment and responsibility.

  • If a person cannot remember an act, are they the same person who did it? Why does Locke still allow the drunkard to be punished?
  • How does Locke's view apply to someone with advanced dementia?

• Chance associations can feel like nature

  In Book II, Chapter XXXIII Locke shows how ideas joined by accident or repetition harden into antipathies, fears and prejudices that reason cannot dissolve, and how time can loosen some of them. He urges parents and teachers to prevent such connexions early.

  • Which of Locke's examples most resembles what we now call conditioning?
  • Why does Locke say time cures some disorders that reason cannot?
  • Is Locke right to call universal habits of association a 'degree of madness'?

• Most of life runs on probability, so judge assent by grounds

  Book IV narrows certain knowledge and leaves most belief to probable judgment. Locke asks that assent be proportioned to evidence and warns that strong inner conviction, as in enthusiasm, proves nothing about truth.

  • How does Locke distinguish legitimate faith from enthusiasm?
  • What would Locke advise someone who is utterly certain because they feel certain?

Context

The Essay appeared in the year after the Glorious Revolution, alongside Locke's political and toleration writings. It drew on the experimental and corpuscular science of the Royal Society, especially Robert Boyle, on the clinical observation Locke learned from Sydenham, and on Gassendi and Descartes. Its critique of innate ideas targeted scholastic authority and the Cambridge Platonists, and its limits on knowledge supported a case for religious moderation.

Composition

The project began in a discussion among friends around 1671, from which two drafts (Drafts A and B) survive. Locke worked on it intermittently for nearly two decades, including in Dutch exile. It was published in London in December 1689 (dated 1690). The second edition (1694) added the chapter on identity and the Molyneux problem; the fourth (1700) added the chapters on association of ideas and on enthusiasm. A French translation by Pierre Coste (1700) spread it across Europe.

Reception

The Essay quickly became the standard philosophical text in Britain and was taught at Oxford, Cambridge and in Dissenting academies. Bishop Stillingfleet attacked its implications for the Trinity and the soul; Leibniz answered it at length in New Essays. Berkeley and Hume radicalized its empiricism, and Voltaire and Condillac made it central to the French Enlightenment. Its chapter on association became the root of associationist psychology through Hartley and the Mills.

Comparisons

• a-treatise-of-human-nature

  Hume adopts Locke's derivation of ideas from experience but drops Locke's distinction of primary and secondary qualities, his unknown substance and his consciousness-based person, and turns association from a source of error into the main engine of thought.

• meditations-on-first-philosophy

  Descartes grounds knowledge in innate ideas and the certainty of the thinking self; Locke's Book I attacks innatism, and his chapter on substance treats the thinking thing as no clearer than matter.

• second-treatise-of-government

  Published the same winter, the Second Treatise relies on the moral claims Locke here says are knowable by reason, and his forensic concept of a person underlies its account of property and consent.

• leviathan

  Hobbes also derives thought from sense and describes trains of imagination, but he is a thoroughgoing materialist; Locke leaves open whether God might give matter the power of thought.

• the-principles-of-psychology

  James's chapters on association, habit and the self engage the tradition Locke's final chapter started, while rejecting the picture of ideas as separate units that mechanically link.

• novum-organum

  Bacon's idols of the mind, especially those of the cave and marketplace, anticipate Locke's analysis of personal associations and the abuse of words as sources of error.

Quotes

For Students

A reading companion for classical Christian high school students. See the student guide.

Reading Guide

Watch for

• The Epistle to the Reader, where Locke tells how a conversation among five or six friends stalled and led him to ask first what the understanding is fitted to deal with. The whole Essay is an answer to that stalled conversation.
• Book I's arguments against innate principles, especially the appeal to children, the uneducated, and the variety of moral rules and ideas of God among peoples.
• The opening of Book II, where Locke supposes the mind to be white paper and asks how it comes to be furnished. Follow the two sources he names, sensation and reflection, through the rest of Book II.
• Book II, Ch. XXVII on identity, with the prince and the cobbler, the waking and sleeping Socrates, and the drunk man punished for what he cannot remember.
• Book IV's closing chapters on faith, reason, and enthusiasm, where Locke says revelation must still be judged by reason and warns against trusting a private inner light.

Key terms and names

Innate principles

Truths supposed to be stamped on the mind from birth, such as whatever is, is, or the idea of God. Book I argues that none commands universal assent and that so-called innate principles are opinions learned early.

Sensation and reflection

The two sources of all ideas in Book II. Sensation gives ideas of external things through the senses, and reflection gives ideas of the mind's own operations, such as thinking, doubting, and willing.

Primary and secondary qualities

Primary qualities such as solidity, extension, and figure resemble the ideas they cause; secondary qualities such as colour, taste, and warmth are only powers in bodies to produce sensations in us, as Locke illustrates with opium.

Molyneux's problem

William Molyneux's question, added in the second edition, whether a man born blind and newly given sight could tell a globe from a cube by sight alone. Locke agrees with Molyneux that he could not without experience.

Substance

The unknown support that we suppose holds a collection of qualities together. In Book II, Ch. XXIII Locke admits our idea of it is only a supposed something we know not what.

Person

In Book II, Ch. XXVII, a forensic term for an agent who can be held accountable. Locke argues that personal identity reaches exactly as far as consciousness reaches back, which separates the same person from the same man.

Association of ideas

Locke's name, in the chapter added in 1700, for ideas joined by chance or custom rather than by nature. His examples include the dancer who needed the trunk in the room and the cured madman who could not bear his operator.

Enthusiasm

In Book IV, the confident claim to private revelation that will not submit its inner light to reason. Locke treats it as a danger to both true religion and civil peace.

Seminar Questions

1. Comprehension What reasons does Locke give in Book I for denying that any speculative or moral principles are innate?
2. Comprehension According to the opening of Book II, from what two sources does the mind receive all its ideas, and what is the difference between them?
3. Comprehension In Book II, Ch. XXVII, why does Locke say the prince's soul in the cobbler's body is the same person as the prince but not the same man?
4. Interpretation Locke describes madmen in Book II, Ch. XI as people who reason rightly from wrongly joined ideas. How does this account connect to the later chapter on the association of ideas, and what does it imply about sane people?
5. Interpretation If our idea of substance is only something we know not what, does Locke's empiricism undermine our confidence that the world is made of real things?
6. Interpretation Locke's own example asks why a drunk man is punished for what he cannot remember. Does his account of the person as consciousness give a good answer, or does the example expose a weakness in it?
7. Interpretation In the Introduction Locke says the candle set up in us shines bright enough for all our purposes. What does he mean, and how does this attitude shape his treatment of faith and enthusiasm in Book IV?
8. Big Question If the mind begins as white paper, where do our convictions about right and wrong and about God come from, and can they still bind us if they are learned rather than inborn?

Faith Connections

• Proverbs 20:27 (Scripture)

  The proverb calls the spirit of man the candle of the Lord. Locke's image in the Introduction of a candle set up in us draws on this language, presenting reason as a God-given light sufficient for the tasks we are given, though not for everything.

• Romans 1:19-20 (Scripture)

  Paul says God's invisible attributes are clearly seen through the things that are made. Locke denies an innate idea of God in Book I but argues in Book IV that God's existence can be demonstrated from our own existence, a path closer to Paul's reasoning from creation.

• 1 Corinthians 13:12 (Scripture)

  Paul says we now see through a glass darkly and know in part. Locke's patient mapping of what the understanding can and cannot reach, from unknown real essences to the limits of probability, is a philosopher's account of knowing in part.

• G. W. Leibniz, New Essays on Human Understanding (Great Conversation)

  Leibniz answered the Essay book by book in a dialogue, defending innate ideas by comparing the mind not to blank paper but to a block of veined marble whose grain already favors certain shapes. Reading the two together sets the white paper of Book II against a mind with its own given structure.

Logic and Rhetoric

Central argument: If any principles were innate, all people, including children and the uneducated, would assent to them; but no principle commands such assent, so none is innate. All ideas must then come from experience, through sensation and reflection. Since knowledge is the perception of agreement or disagreement among our ideas, it can reach only as far as our ideas reach. Therefore we should measure the extent of the understanding, seek certainty where it is available, rely on probability and judgment elsewhere, submit even claims of revelation to reason, and stop disputing about what lies beyond our faculties.

Rhetorical device: governing metaphor. At Book II, Ch. I, §2 Locke asks the reader to suppose the mind to be white paper and then asks how it comes to be furnished. The single image of a blank sheet turned into a furnished room organizes the whole of Book II and made his position memorable to generations of readers.

Debate: Resolved: Locke is right that a person is the same person only as far as his consciousness reaches back.

Memory Work

The Candle that is set up in us shines bright enough for all our purposes

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

Writing Prompts

Essay: Locke separates the identity of a man from the identity of a person in Book II, Ch. XXVII. Using the prince and the cobbler, the waking and sleeping Socrates, and the drunk man punished for a forgotten deed, explain his theory and argue whether it can support the justice of reward and punishment that Locke says it must.

Comparison with Meditations on First Philosophy: Descartes finds the idea of God already in his mind and builds knowledge outward from the thinking self, while Locke denies innate ideas and builds from sensation and reflection. Compare how each philosopher arrives at knowledge of the self and of God, and argue which starting point better accounts for the certainty each claims.

Medical Lens

Locke was a trained physician and close associate of Thomas Sydenham, and the Essay carries Sydenham's preference for observation over speculative theory. For psychiatry it offers an influential cognitive theory of madness (correct reasoning from wrongly joined ideas), which shaped eighteenth-century writing on insanity and the later concept of partial insanity or monomania. The chapter on association reads as a proto-theory of conditioned fear, phobia and context-dependent memory, and its section on grief makes a still-relevant point about the limits of rational consolation. The identity chapter's cases of memory loss, drunkenness and sleepwalking remain central to debates on dementia, dissociation and criminal responsibility. Equating Locke's examples with modern diagnoses is an interpretive move, not a historical claim about his intentions.

• Book II, Ch. IX, §8

  Molyneux's problem: whether a man born blind, newly given sight, could distinguish a globe from a cube without touching them; Locke and Molyneux answer no.

  Disability DeformityMind Body
• Book II, Ch. XI, §12–13

  Difference between 'naturals' (intellectual disability) and madmen; delusions such as believing oneself a king or made of glass; partial madness in otherwise sober people.

  Madness PsychosisObsession MonomaniaAsylum Institution
• Book II, Ch. XXI

  The will determined by present uneasiness; the drunkard who sees his health and estate decaying yet returns to drink.

  AlcoholAddiction
• Book II, Ch. XXIII

  Opium's colour, taste and soporific or anodyne virtues as powers grounded in hidden primary qualities.

  Opium LaudanumPharmacology Poisons
• Book II, Ch. XXVII

  Personal identity through consciousness; cases of forgetting, drunkenness, sleepwalking and alternating consciousness, and their bearing on punishment.

  Dementia MemoryAlcoholSleep InsomniaPsychology Unconscious
• Book II, Ch. XXXIII, §7–16

  Associations producing antipathies (surfeit of honey), fear of the dark, rumination on injury, aversion to places of illness, unending grief, aversion to a surgeon who cured madness, and context-bound dancing.

  Neurosis AnxietyGriefTrauma Shell ShockPsychology Unconscious

Creative Prompts

• Fiction

  Write the story of the gentleman cured of madness by a harsh operation, told on the day he meets his surgeon again in the street.

• Dialogue

  Stage a consultation between Locke, wearing his physician's hat, and Shaftesbury, about whether the person who wakes from the operation will be the same person who consented to it.

• Essay

  Use Locke's memory criterion of personal identity to examine advance directives in dementia: whose wishes should govern?

• Classroom

  Have students design a modern version of Molyneux's experiment and then read about real cases of sight restoration to see whether Locke's answer held.

Further Reading

• Second Treatise of Government, John Locke

• Some Thoughts Concerning Education, John Locke

  Locke's advice on child-rearing, which applies the Essay's warnings about early associations.

• New Essays on Human Understanding, G. W. Leibniz

  A chapter-by-chapter dialogue answering Locke.

• John Locke: A Biography, Maurice Cranston

• Locke, Berkeley, Hume: Central Themes, Jonathan Bennett

• Molyneux's Question: Vision, Touch and the Philosophy of Perception, Michael J. Morgan