Hume's "naturalist" approach to a wide variety of philosophical topics resulted in highly original theories about perception, self-identity, causation, morality, politics, and religion, all of which are discussed in this stimulating introduction by A.J. Ayer, himself one of the twentieth century's most important philosophers. Ayer also gives an account of Hume's fascinating life and character, and includes generous quotations from Hume's lucid and often witty writings.