The books translated in this volume are seventh and eighth in the traditional ordering of Aristotle's Metaphysics. They are central to Aristotle's metaphysical system: in them he discusses the nature of perceptible 'substance' or reality. In particular, he compares the claims of matter and of form to be the basic reality of things, and he frequently contrasts his own view of form with the Platonic view. Several other topics are treated which are of central importance to his metaphysics, e.g. the notions of essence and definition, the status of universals, and the concept of a unity. David Bostock provides an authoritative guide to these difficult and important books, assuming no knowledge of Greek on the part of the reader. He offers a clear new translation that follows the original closely, and a thorough and careful philosophical commentary.