Introduction: Hume’s position in ethics, which is based on his empiricist theory of the mind, is best known for asserting four theses: (1) Reason alone cannot be a motive to the will, but rather is the “slave of the passions” (see Section 3) (2) Moral distinctions are not derived from reason (see Section 4). (3) Moral distinctions are derived from the moral sentiments: feelings of approval (esteem, praise) and disapproval (blame) felt by spectators who contemplate a character trait or action (see Section 7). (4) While some virtues and vices are natural (see Section 13), others, including justice, are artificial (see Section 9). There is heated debate about what Hume intends by each of these theses and how he argues for them. He articulates and defends them within the broader context of his metaethics and his ethic of virtue and vice.
Hume’s main ethical writings are Book 3 of his Treatise of Human Nature, “Of Morals” (which builds on Book 2, “Of the Passions”), his Enquiry concerning the Principles of Morals, and some of his Essays. In part the moral Enquiry simply recasts central ideas from the moral part of the Treatise in a more accessible style; but there are important differences. The ethical positions and arguments of the Treatise are set out below, noting where the moral Enquiry agrees; differences between the Enquiry and the Treatise are discussed afterwards.