In this book, Professor Pears examines the foundations of Hume's system as laid down in the first book of his Treatise, where his ideas are presented in their first fresh and undiluted form. The author steers a middle course between the two extreme views adopted in recent writings on Hume: that he relies exclusively on a theory of meaning, or that he relies exclusively on a theory of truth and evidence. Professor Pears argues that Hume's theory of ideas serves both functions, and he examines in detail its application to three difficult problems: causation, personal identity, and sense-perception. Hume's solutions are shown not to be theories which can be given a place in a standard classification of philosophical theories, but rather to depend upon a subtle form of naturalism not altogether unlike Wittgenstein's naturalism.