  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.