This book is an introduction to the philosophy of logic and an attempt to assess its scope and philosophical significance. The author deals with the nature of proposition, connectives, quantifiers, truth, modality, propositional attitude, and vagueness and deals with the more general questions of realism versus antirealism in logic and of the nature of logical constants. He defends a form of realism based on the idea of logic as a normative discipline setting the general standards of rationality.