A Treatise of Human Nature

Summary

Hume subtitled his first book 'an attempt to introduce the experimental method of reasoning into moral subjects', and he meant it literally: as Newton had explained the heavens by a few observed principles, Hume would explain belief, emotion and morality by a few principles of the mind. Book I, Of the Understanding, begins by dividing all perceptions into vivid impressions and fainter ideas, and holds that every simple idea is copied from a prior impression. Ideas are linked by three associative relations, resemblance, contiguity and cause and effect, which Hume calls a gentle force of attraction in the mental world. The heart of the book is his analysis of causation. We never perceive any necessary connexion between a cause and its effect; we observe only that one kind of event has constantly followed another. Inference from the past to the future cannot be justified by demonstration or by probable reasoning without circularity, so it rests on custom: repeated conjunction produces a felt determination of the mind to pass from one idea to its usual attendant. Belief itself is not a further idea but a manner of conceiving, a greater force and vivacity. Part IV pushes this scepticism further. Our confidence in an external world, in material substance and in an enduring soul all turn out to be products of the imagination. Looking inward, Hume finds no self at all, only a bundle of perceptions in perpetual flux. The book then closes with an extraordinary personal confession: the philosopher, isolated and frightened by his own conclusions, is rescued not by argument but by dinner, backgammon and friends. Book II, Of the Passions, offers a detailed mechanics of pride and humility, love and hatred, built on a double relation of impressions and ideas, and introduces sympathy, the communication of feeling from one person to another, as a fundamental principle of social life. It then argues that reason alone can never motivate action or oppose a passion. Book III, Of Morals, published separately in 1740, concludes that moral distinctions are not discovered by reason but felt through a moral sentiment, notes the illegitimate slide from 'is' to 'ought' in moralists' arguments, and treats justice, property and promising as artificial virtues invented by convention to serve human interest, while benevolence and similar traits are natural virtues approved through sympathy. The young author famously complained that the work 'fell dead-born from the press', yet its arguments on causation, induction, the self and the motivational priority of feeling define problems philosophers still work on.

Plot or Argument

• Impressions, ideas and the copy principle (I.i)

  All perceptions are impressions (sensations, passions) or ideas (their fainter copies). Simple ideas derive from simple impressions; complex ideas are assembled by the imagination under the associative relations of resemblance, contiguity and causation.

• Space, time and the limits of divisibility (I.ii)

  Hume argues that our ideas of space and time are composed of finite minima and attacks the infinite divisibility of extension, an early test of the copy principle against mathematical abstraction.

• Causation, custom and belief (I.iii)

  The idea of necessary connexion has no source in any observed quality of objects. It arises from constant conjunction, which produces a habit of expectation. Belief is a lively idea related to a present impression; education, repetition and even lying can counterfeit this liveliness.

• Scepticism about the world and the self (I.iv)

  Reason, applied to itself, undermines all probability. Belief in continuing external bodies is a fiction of the imagination; so is the simple, identical soul. Personal identity is only a bundle of successive perceptions bound by resemblance and causation.

• The conclusion of Book I: melancholy and its cure

  Hume narrates his own despair at these results, his sense of being a monster expelled from human society, and his recovery through ordinary pleasures. He resolves to philosophize only where reason mixes with a natural propensity.

• The indirect passions and sympathy (II.i–ii)

  Pride, humility, love and hatred are explained by a double relation between an object, a pleasant or painful quality and the self or another person. Sympathy converts the idea of another's feeling into an impression of our own, so that minds reflect one another.

• Will, liberty and the subordination of reason (II.iii)

  Human actions are as regular as natural events, so liberty of indifference is an illusion. Reason discovers relations and means but cannot produce motivation; it is the servant of the passions. What we call reason's victories are calm passions prevailing over violent ones.

• Moral sense and the is–ought gap (III.i)

  Virtue and vice are not matters of fact or relations of ideas. Morality is felt as a peculiar pleasure or uneasiness on contemplating a character, and arguments that move from what is to what ought to be require an explanation they rarely receive.

• Justice as an artificial virtue (III.ii)

  Scarcity, limited generosity and the instability of possessions lead people to conventions of property, transfer by consent and promise-keeping. These rules, and the governments that enforce them, are approved because sympathy with the public interest attaches moral feeling to them.

• Natural virtues and the appendix (III.iii)

  Benevolence, greatness of mind and natural abilities are approved because they are useful or agreeable to their possessor or others. The 1740 appendix admits that Hume's account of personal identity leaves him in a labyrinth he cannot escape.

Characters

• The narrating philosopher, first-person voice

  Hume's own persona, who in the conclusion to Book I describes his solitude, dread and recovery and so turns an epistemological treatise into something like a case history.

• Isaac Newton, model

  Never discussed at length but the implicit pattern for Hume's ambition to find a few general laws of mental attraction.

• John Locke and George Berkeley, predecessors

  Sources of the way of ideas whom Hume cites and corrects, especially on abstract ideas, substance and personal identity.

• Nicolas Malebranche, foil

  Occasionalist whose view that only God is a true cause Hume uses as the extreme case of searching for causal power beyond observed conjunction.

Lessons

• Expectation is a habit of mind, not a perception of necessity

  Hume shows that our confidence that the future will resemble the past cannot be proved, yet we cannot stop relying on it. Custom does the work reason was supposed to do, which makes our most basic inferences natural rather than rational.

  • If causal belief rests on custom, how should we treat a single striking experience versus a long run of observations?
  • Does Hume's account of belief as 'vivacity' explain why vivid anecdotes can outweigh statistics?
  • Can a scientist accept Hume's argument and still do science with confidence?

• Looking inward finds perceptions, never a perceiver

  When Hume searches introspectively for a self, he finds only particular sensations and feelings. The unity we attribute to a person is supplied by the imagination, an idea that troubled Hume himself in the appendix.

  • Is the bundle theory a discovery about the self or a limitation of introspection?
  • How might the bundle view change the way we think about memory loss or dissociation?

• Feeling sets ends; reasoning only finds routes to them

  Book II argues that reason cannot by itself move us to act or oppose a desire. Apparent struggles between reason and passion are really contests between calm and violent passions, so changing behaviour means working on feeling and habit.

  • What would Hume say about someone who knows smoking is harmful and keeps smoking?
  • Are 'calm passions' a convincing name for what we usually call prudence or rational self-interest?
  • Is there any case where a belief alone, without desire, seems to produce action?

• Scepticism is cured by living, not refuted by argument

  The end of Book I dramatizes a philosopher overwhelmed by doubt who recovers through company and play. Hume concludes that nature, not reason, keeps us from total scepticism, and that philosophy should be pursued only in a mood where it remains agreeable.

  • Is Hume's turn to backgammon an evasion or a philosophical position?
  • What does the passage suggest about the emotional costs of intellectual isolation?

Context

Hume wrote in the wake of Locke's Essay and Newton's Principia, when British philosophers were trying to build a science of the mind on observation. Scottish moral philosophers such as Francis Hutcheson had already proposed a moral sense, and Hume extended that sentimentalist approach while turning Lockean empiricism toward radical scepticism. His conclusions on causation, miracles and the soul had obvious religious implications in Presbyterian Scotland.

Composition

Hume planned the book in his late teens and early twenties, through an intellectual crisis around 1729–1734, and wrote most of it in France between 1734 and 1737. He removed passages on miracles to avoid offending Joseph Butler. Books I and II were published anonymously in London in January 1739; Book III, with an appendix, followed in November 1740. Hume also issued an anonymous Abstract (1740) to explain the argument.

Reception

Early reviews were few and mostly hostile or puzzled, and Hume later disowned the Treatise in favour of his recast Enquiries. Its reputation as a youthful work damaged his candidacies for chairs at Edinburgh (1745) and Glasgow (1751–52). Thomas Reid built his common-sense philosophy in reply, and Kant credited Hume with waking him from dogmatic slumber, though Kant knew the Enquiry better. Twentieth-century analytic philosophy treated the Treatise as Hume's fullest statement.

Comparisons

• an-essay-concerning-human-understanding

  Locke supplied the vocabulary of ideas and the empiricist programme; Hume tightens it into the copy principle and turns it against substance and the self, where Locke had kept a 'something I know not what' behind qualities and grounded identity in consciousness and memory.

• an-enquiry-concerning-human-understanding

  Hume's own recasting of Book I: shorter, more elegant, without the analysis of space, external bodies or personal identity, but with new sections on miracles and providence. Reading both shows which arguments Hume chose to keep in public view.

• the-passions-of-the-soul

  Descartes explains emotions by animal spirits acting on the pineal gland and gives the soul power to master them; Hume's Book II keeps a mechanical style of explanation but drops the soul's sovereignty and makes reason the passions' servant.

• ethics

  Spinoza also treats affects with geometrical detachment and denies free will, but hopes adequate ideas can free us from bondage to passion. Hume denies that ideas alone could ever have that power.

• the-principles-of-psychology

  William James inherits Hume's introspective method and his doubts about a substantial soul, but replaces the bundle of discrete perceptions with a continuous 'stream of thought' and criticizes associationism for chopping experience into pieces.

• critique-of-pure-reason

  Kant accepts that causal necessity cannot be found in experience and responds by making causality a category the mind imposes, turning Hume's custom-based psychology into a theory of a priori conditions of experience.

Quotes

For Students

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

Reading Guide

Watch for

• The copy principle at the opening of Book I: every simple idea comes from a prior impression. Hume uses it as a test throughout, asking of any idea, from what impression is it derived?
• The search for necessary connexion in Book I, Part III. Follow Hume as he looks for the impression behind our idea of cause and finds only constant conjunction and the mind's habit of expectation.
• Of Personal Identity, Book I, Part IV, Section 6, where Hume looks inward for a self and finds only perceptions, comparing the mind to a theatre.
• The Conclusion of Book I, an unusual personal passage in which Hume describes the melancholy his own arguments produce and how dinner, backgammon, and friends restore him.
• Book II, Part III, Section 3, where Hume argues that reason alone can never move the will, and Book III, Part I, where he observes that moralists slip from is to ought without explaining how.

Key terms and names

Impressions and ideas

Hume's two kinds of perception. Impressions are vivid sensations and passions; ideas are their fainter copies in thought and memory. The difference between them, for Hume, is only one of force and liveliness.

Constant conjunction

The repeated observation that one kind of event follows another. Hume argues in Book I, Part III that this is all we ever observe of causation; the necessity we feel is added by the mind.

Custom

The habit produced by repeated experience that carries the mind from a cause to its usual effect. Hume makes custom, not reasoning, the foundation of every inference about matters of fact.

Bundle theory

Hume's account in Book I, Part IV, Section 6 that the self is nothing but a bundle of perceptions in perpetual flux. He confesses in the Appendix that he cannot fully explain what binds the bundle together.

Sympathy

Hume's name in Book II for the way feelings pass from one person to another, so that minds become mirrors to one another. It is the foundation of his account of social life and moral approval.

Is and ought

Hume's observation in Book III, Part I, Section 1 that moral writers move from statements of fact to statements of obligation without justifying the step. The passage has framed debate about the foundations of ethics ever since.

Artificial virtue

Hume's term in Book III, Part II for justice, property, and promise-keeping, which he holds are invented by human convention to serve common interest, in contrast to natural virtues such as benevolence.

Seminar Questions

1. Comprehension What is the difference between an impression and an idea, and what does Hume mean by saying simple ideas are copies of impressions?
2. Comprehension According to Book I, Part III, what do we actually observe when we say that one billiard ball causes another to move, and what does the mind add?
3. Comprehension In the Conclusion of Book I, what state does Hume say his philosophy has left him in, and what cures him of it?
4. Interpretation Hume says reason is and ought only to be the slave of the passions. Is he saying people should be ruled by their feelings, or describing how motivation works? What does his distinction between calm and violent passions add?
5. Interpretation When Hume looks inward he never catches himself without a perception. Does this show there is no self, or only that the self is not the kind of thing that can be observed as an object?
6. Interpretation Hume admits that nature, not reason, rescues him from philosophical melancholy. Does this confession strengthen his skepticism or weaken it?
7. Interpretation If justice is an artificial virtue invented for human convenience, as Book III argues, why does Hume think we still feel moral approval for it and not merely self-interest?
8. Big Question If our confidence that the sun will rise tomorrow rests on custom and not on demonstration, is it still rational to hold it? What must be true about the world, and about us, for experience to be trustworthy?

Faith Connections

• Romans 1:20 (Scripture)

  Paul says the invisible things of God are clearly seen, being understood by the things that are made. Hume's analysis of causation in Book I questions whether we can ever reason from observed effects to an unobserved cause, so this verse and the Treatise together frame the central debate over natural theology.

• Psalm 139:1-6 (Scripture)

  The psalmist confesses that God has searched and known him, his sitting down and rising up, his thoughts afar off, a knowledge too wonderful for him. Where Hume, looking inward, finds only passing perceptions, the psalmist locates the unity of the self in being known by Another.

• Augustine, Confessions X (Church Fathers)

  Augustine explores the vast halls of memory and confesses that he has become a great question to himself and cannot grasp all that he is. Like Hume, he finds the self elusive to introspection, but he treats that mystery as a path toward God rather than as evidence that there is no enduring soul.

• Thomas Reid, An Inquiry into the Human Mind on the Principles of Common Sense (1764) (Great Conversation)

  Reid, a Scottish minister and professor, argued that Hume's skepticism followed from the theory of ideas Hume inherited from Locke, and that principles such as belief in an external world and in our own continuing existence are first principles of common sense. Hume's own appeal to nature in the Conclusion of Book I is the point where the two Scots come closest.

Logic and Rhetoric

Central argument: All ideas are copied from impressions. We have no impression of necessary connexion between cause and effect, only of constant conjunction; therefore our idea of causal necessity comes from custom, the mind's habit of expecting what has usually followed. The same test, applied to the external world and the self, finds no impression of either, so belief in them is also a product of imagination. Since reason cannot ground these beliefs and yet nature compels us to hold them, the proper course is a mitigated skepticism that follows reason only where it is mixed with natural propensity, and a science of man built on feeling: reason serves the passions, and morality is more properly felt than judged.

Rhetorical device: extended analogy. In Book I, Part IV, Section 6 Hume compares the mind to a theatre where perceptions pass, re-pass, glide away, and mingle. He then immediately warns that the comparison must not mislead us, since there is no stage and no audience, only the perceptions, so the analogy carries his argument and corrects itself at once.

Debate: Resolved: Hume is right that moral distinctions are derived from feeling rather than from reason.

Memory Work

Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them

I dine, I play a game of backgammon, I converse, and am merry with my friends

Writing Prompts

Essay: In the Conclusion of Book I Hume says nature cures him of the philosophical melancholy his reasoning produced. Using his analysis of causation, his account of personal identity, and this conclusion, argue whether Hume's skepticism is a position he actually holds or a discovery about the limits of philosophy.

Comparison with Pensees: Pascal and Hume both argue that reason cannot by itself establish the beliefs we live by, and both turn to something other than demonstration: for Pascal the heart and the wager, for Hume custom and natural propensity. Compare their accounts of where reason fails and argue which offers the more satisfying answer to the doubt it raises.

Medical Lens

The Treatise is a founding text of associationist psychology, the tradition that runs through David Hartley and James Mill to nineteenth-century physiological psychology. For psychiatry its richest pages are the conclusion to Book I, a first-person account of 'philosophical melancholy and delirium' relieved by company and diversion, which readers often set beside Hume's 1734 letter to an unnamed physician (often identified as George Cheyne or John Arbuthnot) describing his breakdown in terms of the 'disease of the learned'. Linking the two is an interpretation, not a diagnosis. Hume's account of madness as excessive vivacity of ideas, and of belief as a feeling rather than a judgment, bears on modern discussions of delusion. His claim that reason cannot by itself motivate is a reference point in debates about insight, akrasia and the limits of purely cognitive therapy. Sympathy in Book II anticipates later work on emotional contagion and empathy.

• Book I, Part III, Sect. 9–10

  Repetition, education and lying give ideas the vivacity of belief; a lively imagination can degenerate into madness when a ferment of the blood and spirits makes fictions indistinguishable from memories.

  Madness PsychosisHumoral MedicineDementia Memory
• Book I, Part IV, Sect. 6

  Introspective search for the self finds only perceptions; the mind compared to a theatre with no fixed stage; sleep and death as the absence of a perceiving self.

  Psychology UnconsciousMind Body
• Book I, Part IV, Sect. 7

  Hume's despair, dread of error, sense of monstrous isolation and 'heated' brain, followed by recovery through dining, backgammon and conversation; he names his mood a splenetic humour.

  Melancholia DepressionNeurosis AnxietyPhilosophy AS TherapyHumoral Medicine
• Book II, Part I, Sect. 11; Part II, Sect. 5

  Sympathy as the communication of passions between people, including how the opinions of others sustain pride and how feelings reverberate between minds.

  Psychology Unconscious
• Book II, Part III, Sect. 3–4

  Reason as servant of the passions; calm versus violent passions; why strong emotion can override clear knowledge of one's interest.

  Mind BodyPsychology Unconscious

Creative Prompts

• Fiction

  Write the evening at La Flèche after Hume finishes the conclusion to Book I: the backgammon game, the friends, and what he does not tell them.

• Dialogue

  Stage a conversation in which a patient with depersonalization describes their experience and Hume replies using only the resources of the bundle theory.

• Essay

  Compare Hume's cure for 'philosophical melancholy' with behavioural activation in modern treatment of depression. Where is the analogy illuminating, and where is it anachronistic?

• Classroom

  Have students keep a two-day log of every causal expectation they act on, then test which ones they could justify without appeal to past regularity.

Further Reading

• An Enquiry Concerning Human Understanding, David Hume

  Hume's later, shorter treatment of Book I's themes.

• My Own Life, David Hume

  Hume's brief autobiography, written in 1776, including the 'dead-born' remark.

• The Philosophy of David Hume, Norman Kemp Smith

  The classic naturalist reading, emphasizing feeling over scepticism.

• Hume's Philosophical Politics, Duncan Forbes

• The Life of David Hume, Ernest Campbell Mossner

• Hume, Barry Stroud

  Analytic study of Hume's theory of mind and causation.