This is a philosophical study of the theory of mind and morality that David Hume developed in his Treatise of Human Nature and other writings. The chief elements in this theory of mind are Hume's accounts of reasons for action and of the complex interrelations of desire, volition, and affection. On this basis, the book lays out and defends Hume's thoroughgoing non-cognitivist theory of moral judgement, and shows that cognitivist and standard sentimentalist readings of Hume are unsatisfactory, as are the usual interpretations of his views on the connections between morality, justice, and convention.