This book originated in the deeply felt conviction that the widespread acceptance of Gettier-type counterexamples to the classical definition of knowledge rests in a demonstrably erroneous understanding of the nature of human knowledge. In seeking to defend that conviction, the author offers a detailed and systematic picture of the nature and limits of human factual knowledge. He defends a fallibilism which, when properly delineated, requires repudiating any classical correspondence theory of truth without at the same time rejecting that core of classical realism which distinguishes it from every idealism denying that we have some correct beliefs about an external world.