An Enquiry Concerning Human Understanding

Summary

Hume first published this book in 1748 as Philosophical Essays Concerning Human Understanding, and gave it its present title in 1758. It is his deliberate second attempt at the material of Book I of the Treatise, written, he said, so that the argument would no longer fail through its manner. In twelve compact sections it drops the Treatise's arguments about space, external bodies and personal identity and adds new and provocative sections on miracles and on providence. Section I defends 'accurate and abstruse' philosophy against the charge that it is useless, while warning in nature's voice that the thinker must remain a man of action and society. Section II restates the distinction between impressions and ideas and challenges anyone who doubts the copy principle to produce an idea with no source in experience, conceding only the puzzle of a missing shade of blue. Section IV divides all objects of enquiry into relations of ideas, which can be known by demonstration, and matters of fact, which cannot. Every inference about unobserved matters of fact depends on cause and effect, and our knowledge of causes comes only from experience. But reasoning from experience presupposes that the future will resemble the past, which no argument can establish without circularity. Section V answers the doubt not with a proof but with a description: custom is the principle that leads us to expect similar effects, and belief is a more vivid, steady conception produced by it. Section VII seeks the origin of the idea of power or necessary connexion and finds it neither in bodies nor in our experience of the will, but in the felt transition of the mind after repeated conjunctions, yielding Hume's two definitions of cause. Section VIII reconciles liberty and necessity: human conduct shows the same uniformity as nature, and liberty means only acting according to one's determinations of the will. Section IX holds that animals learn from experience by the same custom. Section X argues that because testimony is itself a matter of probability, a wise man proportions belief to evidence, and no testimony can establish a miracle unless its falsehood would be more miraculous than the event it reports; Hume illustrates with reported Jansenist cures at the tomb of the Abbé Pâris. Section XI, a dialogue with a sceptical friend who speaks as Epicurus, questions whether order in nature can support inferences to a providential God. Section XII distinguishes excessive Pyrrhonian doubt, which nature overrules, from a mitigated scepticism that confines enquiry to common life and experiment, and ends by advising readers to commit books of divinity and school metaphysics to the flames.

Plot or Argument

• Sect. I: The two species of philosophy

  Hume compares easy moral writing with abstract analysis and defends the latter as the only cure for superstition disguised as metaphysics, while insisting that philosophy remain humane and connected to action.

• Sect. II–III: Origin and association of ideas

  Ideas are less lively copies of impressions; the most vivid thought is weaker than the dullest sensation unless the mind is disordered. Ideas are connected by resemblance, contiguity and causation.

• Sect. IV: Sceptical doubts about the understanding

  Relations of ideas versus matters of fact (later called Hume's fork). No a priori reasoning shows what effect follows a cause, and arguments from experience assume the uniformity they are meant to prove.

• Sect. V: The sceptical solution

  Custom, not reasoning, carries us from past conjunctions to expectations; belief is a manner of feeling an idea. Nature has secured this vital operation by an instinct rather than by fallible argument.

• Sect. VI–VII: Probability and necessary connexion

  Probabilities arise from mixed experience. The idea of power is copied not from anything in objects or in the will's command over body and mind, but from the mind's customary transition, giving two definitions of cause.

• Sect. VIII: Liberty and necessity reconciled

  History and daily life show regular connexions between motives and actions, which we rely on as we rely on physical laws. Liberty is the power of acting or not according to the will, compatible with necessity.

• Sect. IX: Reason in animals

  Beasts learn from experience and form expectations by the same custom as humans, which confirms that experimental reasoning is an instinct.

• Sect. X: Of miracles

  Testimony is weighed like any other evidence. A miracle, a violation of the laws of nature, faces the full weight of uniform experience; historical reports of miracles come from credulous ages and interested witnesses. Reported cures at the Abbé Pâris's tomb show that even well-attested wonders should be rejected.

• Sect. XI: Providence and a future state

  A friend speaking for Epicurus argues that from an imperfect world we cannot infer a cause with greater qualities than the effects display, so religious hypotheses add nothing to the conduct of life.

• Sect. XII: Mitigated scepticism

  Cartesian antecedent doubt and Pyrrhonian excessive doubt are both unliveable. A modest academic scepticism limits enquiry to mathematics and experimental reasoning and consigns the rest to the flames.

Characters

• The sceptical friend, interlocutor (Sect. XI)

  An unnamed friend 'who loves sceptical paradoxes' and delivers a speech in the person of Epicurus defending himself before the Athenians.

• Abbé François de Pâris, historical example (Sect. X)

  Jansenist deacon whose tomb in the cemetery of Saint-Médard became the site of reported miraculous cures and convulsions in the 1720s–1730s.

• Pyrrho and the Pyrrhonians, foil (Sect. XII)

  Ancient sceptics whose total suspension of belief Hume argues no one can live by.

Lessons

• Proportion belief to the weight of the evidence

  Hume's rule for testimony applies to every claim: weigh the reliability of the source against the improbability of what is reported. The more an event conflicts with uniform experience, the stronger the testimony must be.

  • How would Hume evaluate a single case report of a dramatic, unexpected recovery?
  • Is it ever reasonable to believe testimony of something without precedent?
  • Which of Hume's four reasons for doubting historical miracle reports applies to modern health misinformation?

• Every argument from experience rests on an unproven assumption

  Section IV shows that the inference from observed to unobserved cases cannot be justified without assuming nature is uniform. Section V shows we make the inference anyway, by custom, which is why the problem of induction is a fact about us as much as about logic.

  • Why does Hume think no argument could ever settle the problem of induction?
  • Does it matter for practice that induction cannot be justified, if it works?

• Freedom does not require exemption from causes

  Section VIII argues that we already treat human motives as regular causes in history, law and daily life. Liberty is acting according to one's own will, not uncaused action, and responsibility depends on that connexion.

  • If behaviour is as predictable as Hume claims, what remains of praise and blame?
  • How does Hume's view bear on treating conduct that follows from illness rather than from settled character?

• Doubt should be moderate enough to live with

  Hume rejects both dogmatism and total scepticism. Nature defeats extreme doubt in practice, so the useful lesson of scepticism is modesty: limit enquiry to what experience can check and remain open to correction.

  • What is the difference between Pyrrhonian and mitigated scepticism in practice?
  • Is Hume's call to burn metaphysics consistent with his own philosophical writing?

Context

The Enquiry belongs to the moment when Newtonian science, deist controversy and the rise of polite essay-writing were reshaping British intellectual life. Its section on miracles entered a lively debate among deists such as Thomas Woolston and defenders of Christian evidences such as Thomas Sherlock. The Saint-Médard cures, which Hume heard about in France, had become a European controversy about Jansenism, convulsionaries and medical testimony.

Composition

Hume wrote it in the mid-1740s, partly while travelling as secretary to General James St Clair. Published in London in 1748 as Philosophical Essays Concerning Human Understanding, it was retitled An Enquiry in the 1758 edition and revised through later editions of his Essays and Treatises on Several Subjects. In the posthumous 1777 edition an advertisement asked readers to judge his philosophy by this work rather than the Treatise.

Reception

The miracles section provoked replies from William Adams, George Campbell and others, and Hume's reputation for scepticism grew. Kant's response, especially in the Prolegomena, was shaped by this book's treatment of causation. Later empiricists from Mill to the logical positivists adopted the fork between relations of ideas and matters of fact, and the closing 'commit it then to the flames' became a motto of anti-metaphysical philosophy.

Comparisons

• a-treatise-of-human-nature

  The Treatise's Book I is the longer original; the Enquiry trims its theory of space, external objects and the self, softens the confessional despair, and adds the explosive argument against miracles.

• dialogues-concerning-natural-religion

  Section XI's speech for Epicurus is a sketch of the critique of the design argument that Hume developed at full length, and with more voices, in the posthumous Dialogues.

• critique-of-pure-reason

  Kant took up Hume's question how we can know necessary connexion and answered that causality is an a priori category, rescuing synthetic necessity that Hume had traced to custom.

• novum-organum

  Bacon's call to build knowledge by careful induction from particulars is exactly what Hume shows cannot be justified by reason, even as he endorses experimental reasoning as the only path to matters of fact.

• meditations-on-first-philosophy

  Section XII names Descartes's universal doubt as an 'antecedent' scepticism that, if possible, would be incurable; Hume's alternative begins inside experience and never expects a foundation of certainty.

• the-varieties-of-religious-experience

  James studies religious experience as psychological data, including healing and conversion, where Hume weighs reports of the miraculous only as testimony to be discounted.

Quotes

For Students

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

Reading Guide

Watch for

• Section IV's division of all objects of enquiry into relations of ideas and matters of fact, and Hume's challenge to say what justifies our belief that the future will resemble the past.
• The turn in Section V from doubt to description, where Hume stops looking for an argument and names custom as what actually carries us from past to future.
• The search in Section VII for the idea of power or necessary connexion, first in bodies, then in the will, and finally in the mind's own felt transition after repeated conjunctions.
• The structure of Section X: Part I gives the general argument about testimony and the laws of nature, and Part II gives the historical reasons for distrusting reports, ending with the cures at the tomb of the Abbé Pâris.
• The closing pages of Section XII, where Hume asks two questions of any volume of divinity or school metaphysics and pronounces the sentence of the flames.

Key terms and names

Impressions and ideas

Hume's two kinds of perception in Section II: impressions are lively sensations and feelings, and ideas are their fainter copies. Every genuine idea, he claims, can be traced back to an impression, with the missing shade of blue as his one admitted puzzle.

Relations of ideas

Truths, such as those of geometry and arithmetic, that can be known by thought alone because their denial would be a contradiction. Hume sets them against matters of fact in Section IV.

Matters of fact

Truths about what exists or happens, whose denial is always conceivable, such as that the sun will rise tomorrow. Section IV argues that all reasoning about them rests on cause and effect, known only by experience.

Custom

The habit formed by repeated experience that leads the mind, after seeing one event, to expect its usual companion. Section V makes custom, not reason, the source of our expectations about the world.

Necessary connexion

The supposed bond between cause and effect that makes the effect follow. Section VII finds no impression of it in objects and traces the idea to the mind's customary transition from one event to the next.

Miracle

Defined in Section X as a violation of the laws of nature. Because those laws rest on uniform experience, Hume argues, testimony to a miracle must always be weighed against the strongest possible evidence on the other side.

Mitigated scepticism

The modest academic scepticism of Section XII, which rejects both Descartes's antecedent doubt and total Pyrrhonian doubt and confines enquiry to mathematics, experiment, and common life.

Seminar Questions

1. Comprehension What is the difference between relations of ideas and matters of fact in Section IV, and which kind of knowledge depends on cause and effect?
2. Comprehension According to Section V, if reason does not lead us to expect the future to resemble the past, what does?
3. Comprehension How does Hume define a miracle in Section X, and what four reasons does Part II give for distrusting historical reports of miracles?
4. Interpretation Hume calls Section V a sceptical solution to the doubts of Section IV. Is it really a solution, or a confession that the doubts cannot be answered?
5. Interpretation In Section VIII Hume argues that liberty and necessity are compatible. What does he mean by liberty, and is that the freedom a person needs in order to be praised or blamed?
6. Interpretation Section X's maxim says testimony can establish a miracle only if its falsehood would be more miraculous than the event reported. Does the argument assume from the start that no miracle has ever happened?
7. Interpretation Why does Hume insist in Section XII that Pyrrhonian doubt is overruled by nature, and how does that fit with his advice in Section I to remain a man amid all one's philosophy?
8. Big Question If our confidence in the regularity of nature rests on custom rather than reason, is our confidence in anything, including Hume's own argument, better grounded than the belief he asks us to give up?

Faith Connections

• 1 Corinthians 15:12-19 (Scripture)

  Paul stakes the whole faith on a reported event, the resurrection, and points to named witnesses still living. Hume's Section X is aimed squarely at this kind of claim, so the two texts together pose the question of what testimony can bear.

• John 20:24-29 (Scripture)

  Thomas refuses to believe the other disciples' testimony until he sees and touches the risen Christ, and Jesus blesses those who believe without seeing. The scene sets Hume's demand for proportioned evidence beside a different account of how faith receives witness.

• Augustine, City of God XXI.8 (Church Fathers)

  Augustine argues that a portent happens not against nature but against what is known of nature. His view challenges Hume's definition of a miracle as a violation of the laws of nature, which Section X takes as its starting point.

• George Campbell, A Dissertation on Miracles (1762) (Great Conversation)

  The Scottish minister Campbell replied directly to Section X, arguing that our natural trust in testimony comes before experience and is not simply derived from it as Hume claimed. His reply is one of the earliest and most careful answers to Hume on this ground.

Logic and Rhetoric

Central argument: All reasoning about matters of fact depends on cause and effect. Our knowledge of cause and effect comes only from experience, and inferring from experience assumes that the future will resemble the past, which cannot be proven without circularity. Therefore our beliefs about the world rest on custom, not reason. Since custom is a natural instinct we cannot abandon, we should neither despair nor doubt everything, but limit our enquiries to mathematics, experiment, and common life, and proportion belief to evidence, which rules out accepting testimony to miracles and speculative metaphysics.

Rhetorical device: hypophora. At the end of Section XII Hume takes a volume of divinity or school metaphysics in hand, asks whether it contains abstract reasoning about quantity or number and whether it contains experimental reasoning about fact and existence, answers each in turn, and then delivers the verdict, Commit it then to the flames. The questions and answers make the reader feel the conclusion has been reached by a simple test.

Debate: Resolved: Hume's argument in Section X gives a reasonable person sufficient grounds to reject all testimony to miracles.

Memory Work

Custom, then, is the great guide of human life

A wise man, therefore, proportions his belief to the evidence

Writing Prompts

Essay: In Section X Hume argues that no testimony can establish a miracle unless its falsehood would be more miraculous than the event it reports. Reconstruct the argument of Part I step by step, then evaluate whether it depends on the conclusions about cause and custom reached in Sections IV and V.

Comparison with Pensees: Hume holds that custom and nature, not reason, carry us through life, and Pascal holds that the heart has reasons that reason does not know. Compare how each thinker limits the power of reason, and argue whether Pascal's account leaves more room for faith than Hume's mitigated scepticism.

Medical Lens

The Enquiry is a foundational text for evidence-based reasoning. Its treatment of probability, irregular causes (rhubarb and opium do not act the same on everyone), testimony and the weighing of extraordinary claims maps closely onto modern questions about case reports, placebo responses and therapeutic claims. Section X examines testimony to miraculous cures at Saint-Médard, including a physician's examination of a reported patient, which makes it an early study of how medical witnesses can be enlisted for the improbable. Section VII's remark that self-command varies with sickness, time of day and fasting is a small but striking observation about state-dependent cognition. Section I's warning that abstruse thought brings 'pensive melancholy' echoes Hume's own youthful breakdown, though that connection is biographical inference.

• Section I

  Nature warns that excessive abstract study will be punished by pensive melancholy, uncertainty and cold reception, and recommends a mixed life of thought, action and society.

  Melancholia DepressionPhilosophy AS Therapy
• Section II

  Ideas can approach the vividness of sensations only when the mind is disordered by disease or madness.

  Madness Psychosis
• Section VI

  Irregular causes such as rhubarb as a purge and opium as a soporific, used to explain how probability arises from mixed experience.

  Pharmacology PoisonsOpium Laudanum
• Section VII, Part I

  The will's command over body and mind is known only by experience; self-command varies with health, sickness, time of day and fasting; a paralysed limb illustrates our ignorance of the mechanism.

  Mind BodyDisability Deformity
• Section VIII, Part I

  Physicians are not surprised when medicines fail, because they assume hidden causes in the animal economy; Hume uses this to argue for regularity in human conduct.

  Physicians DoctorsPharmacology Poisons
• Section X, Part II and notes

  Reported miraculous cures at the tomb of the Abbé Pâris, with physicians and witnesses for and against, including the case of Mademoiselle Thibaut.

  Physicians DoctorsQuackery Charlatans

Creative Prompts

• Essay

  Apply Hume's test for miracles to a contemporary claim of a dramatic drug response reported in a single patient. What would Hume require before believing it?

• Dialogue

  Write the exchange between Hume and a physician who examined a patient cured at Saint-Médard and is convinced the cure was real.

• Classroom

  Give students five claims of increasing improbability and ask them to apply Hume's rule of proportioning belief to evidence, then discuss where Bayesian reasoning agrees or departs.

• Fiction

  Tell the story of a librarian in 1760 who takes Hume's last paragraph literally and must decide which books to burn.

Further Reading

• A Treatise of Human Nature, David Hume

• An Enquiry Concerning the Principles of Morals, David Hume

  The companion recasting of Treatise Book III.

• Prolegomena to Any Future Metaphysics, Immanuel Kant

  Kant's account of being woken from dogmatic slumber by Hume.

• Hume's Abject Failure: The Argument Against Miracles, John Earman

  A probabilistic critique of Section X.

• The Life of David Hume, Ernest Campbell Mossner