"Know thyself," a precept as old as Socrates, is still good advice. But is introspection the best path to self-knowledge? What are we trying to discover, anyway? In an eye-opening tour of the unconscious, as contemporary psychological science has redefined it, Timothy D. Wilson introduces us to a hidden mental world of judgments, feelings, and motives that introspection may never show us.

This is not your psychoanalyst's unconscious. The adaptive unconscious that empirical psychology has revealed, and that Wilson describes, is much more than a repository of primitive drives and...