This book weaves together concerns from three different literatures in philosophy: the logical analysis of propositional attitude reports (Quine), the semantics and metaphysics of cognition (Fodor, Putnam, Burge), and issues of causation and externalism in epistemology (Gettier, Goldman, Lehrer). The topics these literatures deal with fit naturally together, but the literatures do not. Often ideas are developed in isolation from the others; sometimes authors in one area see the relevance of the others, but do not have the patience to get things straight. This work is based on the version of Philip R. Henry's dissertation that was left behind after his untimely death in 1987. Professor Julius Moravscik, Henry's advisor, and Professor John Perry, a member of Henry's committee, felt it worthwhile to make the ideas of this serious and talented philosopher available to the philosophy community.