The contains some of Aristotle's most influential thoughts in logic, epistemology, metaphysics, and the philosophy of science. The first book expounds and develops the notions of a demonstrative argument and of a formal, axiomatized science; the second discusses a cluster of problems raised by the axioms or principles of such a science, and investigates in particular the theory of definition. This volume is intended to serve the needs of readers of Aristotle without a knowledge of Greek; for this second edition the translation has been completely rewritten, with the aims of greater elegance and greater fidelity to the Greek. The commentary elucidates and assesses Aristotle's arguments from a philosophical point of view; it has been extensively revised to take account of the scholarship of the last twenty years.