Book: A Treatise of Human Nature

Overview

David Hume’s A Treatise of Human Nature (1739, 40) aims to found the sciences on a systematic account of human nature. Rejecting rationalist claims to innate ideas and necessary truths about the world, Hume advances a thoroughgoing empiricism: all the contents of the mind derive from experience, and the mind’s operations can be explained by psychological principles. The work is divided into three books, Of the Understanding, Of the Passions, and Of Morals, each developing a naturalistic account of cognition, motivation, and ethics that both exposes the limits of reason and explains how belief, action, and moral evaluation nevertheless arise.

Book I: Of the Understanding

Hume begins with the “copy principle”: all ideas are faint copies of antecedent impressions (vivid sensory or emotional experiences). He analyzes how ideas are associated by resemblance, contiguity, and especially cause and effect. The notion of causation does not arise from perceiving a necessary connection in nature; we observe only constant conjunction and infer a connection by habit or custom. Belief is not a special idea but a lively or vivacious manner of conceiving an idea produced by repeated conjunctions. This diagnosis underwrites the problem of induction: there is no demonstrative or probable proof that the future will resemble the past; the expectation of uniformity is a nonrational but natural propensity.

He criticizes the doctrine of abstract ideas, explaining apparent generality through the mind’s capacity to use particular ideas in a general way. On space and time, he treats them as collections of minimal, indivisible perceptions, challenging substantive metaphysical accounts. His account of personal identity is likewise deflationary: the self is not an invariant substance but a bundle or heap of perceptions related by resemblance and causation. Our belief in a continued, independent world similarly rests on the imagination’s propensity to feign stability across interrupted perceptions. Throughout, skeptical arguments unsettle rational pretensions, while a naturalistic psychology explains why we inevitably form beliefs and navigate the world.

Book II: Of the Passions

Turning to motivation, Hume argues that reason alone cannot move the will; it discovers relations of ideas and matters of fact but does not supply ends. The passions provide the motives, and reason serves them, famously, it is the slave of the passions. He distinguishes direct passions, such as desire, aversion, hope, and fear, from indirect passions, notably pride and humility, love and hatred, which arise through a “double relation” of impressions and ideas connecting the self, its qualities, and their pleasurable or painful effects. Sympathy transmits sentiments across persons, explaining how we are affected by others’ fortunes and opinions. On liberty and necessity, Hume defends a compatibilist view: regular connections between motives and actions are necessary for responsibility, and moral appraisal tracks character revealed in consistent patterns of behavior.

Book III: Of Morals

Moral distinctions stem from sentiment rather than reason. We approve or disapprove of traits by feeling their agreeableness or usefulness to ourselves and others from a general point of view that corrects for partiality. Hume distinguishes natural virtues, like benevolence and generosity, from artificial virtues, such as justice and fidelity, which arise from social conventions coordinating limited generosity and scarce resources. Justice, property, and promising are stabilized by rules that serve public utility; government and allegiance rest on similar considerations. He articulates the is, ought gap, warning that prescriptive conclusions do not follow without a normative premise. Moral language, on his account, expresses refined sentiments informed by sympathy and social utility, not discoveries of objective moral facts known by reason.

Significance

The Treatise unifies epistemology, psychology, and ethics under an empirical method, pairing deep skepticism about rational foundations with a constructive explanation of belief, motivation, and morality in terms of human nature. Its analyses of causation, induction, the self, and moral sentiments have shaped modern philosophy and the human sciences.