Corresponding scope: Books I–III (overall synthesis)

This unit provides a structural overview of the three books of the Treatise. Book I examines the understanding, focusing on ideas, causation, belief, and the self, and establishes an empiricist account that limits the authority of reason. Book II analyzes the passions and argues that action is motivated by sentiment rather than reason, assigning reason an instrumental role. Book III addresses morals, locating moral judgment in sentiment and social psychology rather than in rational deduction, and distinguishing natural from artificial virtues.

Together, the three books form a continuous progression from cognition to action to normativity. Knowledge is grounded in experience, habit, and psychological association rather than necessity; action is driven by passion rather than reason; moral evaluation arises from sentiment and social utility. Justice, as an artificial virtue, illustrates how moral norms gain stability through convention under specific social conditions.

The Treatise thus presents a unified project: to replace traditional metaphysical philosophy with a systematic science of human nature.

Corresponding section: Book III, Part III (Of Justice)

In Book III, Part III of the Treatise, Hume offers a focused account of justice and distinguishes it from other moral virtues. He argues that justice is not a natural virtue but an artificial one, arising only under specific social conditions.

According to Hume, justice becomes necessary because of three circumstances: the scarcity of resources, the predominance of self-interest, and the limited extent of human benevolence. Under these conditions, natural sentiments alone are insufficient to sustain social order, and rules are introduced through convention to regulate property, promises, and conduct.

Justice therefore differs from virtues such as benevolence, which arise directly from natural feeling. Rules of justice are initially followed not because they are perceived as morally good, but because they serve the public interest. Over time, their utility is felt through sympathy, and justice acquires moral approval.

Hume concludes that the moral status of justice is not original but derived from its social usefulness.

Corresponding sections: Book III (Of Morals), mainly Parts I–II

In Book III of the Treatise, Hume examines the origin and nature of moral judgment. His central claim is that moral distinctions are not derived from reason but from sentiment. Reason can discover facts and relations, but it cannot generate judgments of virtue, vice, or obligation.

Hume distinguishes factual judgments from moral evaluations. Moral judgments do not describe properties of objects; rather, they express emotional responses that arise when we contemplate actions and characters. Morality, therefore, is not found in the object but in the observer’s sentiment.

Hume further argues that sympathy is the key mechanism underlying moral judgment. Through sympathy, individuals share in the feelings of others, allowing moral approval and disapproval to extend beyond private interest. This shared psychological structure gives moral judgments a degree of generality.

Accordingly, morality is grounded not in reason but in passions, sentiments, and common human psychology.