This collection of John Mackie's papers on topics in epistemology, some of which have not previously been published, deal with such issues as: incorrigible empirical statements; rationalism and empiricism; the philosophy of John Anderson; self-refutation; Plato's theory of idea; ideological explanation; problems of intentionality; Popper's third world;; mind, brain, and causation; Newcomb's Paradox and the direction of causation; induction; causation in concept, knowledge, and reality; absolutism; Locke and representative perception; and anti-realisms.