This book offers a comprehensive analysis and re-evaluation of Hume's Treatise of Human Nature. Kant viewed Hume as the sceptical destroyer of metaphysics. Yet for most of this century the consensus among interpreters is that for Hume scepticism was a means to a naturalistic, anti-sceptical end. The author seeks here to achieve a balance by showing how Hume's naturalism leads directly to a kind of scepticism even more radical than Kant imagined. In the process it offers the first systematic treatment of Humean associationalist psychology, including detailed exploration of his views on time-consciousness, memory, aspect-seeing, and the comparison with animal reason. Within this framework, Hume's views on language, belief, induction, causality, and personal identity emerge in a novel and revealing light.