An investigation into Aristotle's metaphysics of nature as expounded in the Physics. It focuses in particular his conception of change, a concept which is shown to possess a unique metaphysical structure, with implications that should engage the attention of contemporary analysis. First published in hardback in 1982, the book is now available for the first time in paperback. 'A powerful and appealing explanatory scheme which succeeds on the whole in drawing together a great many seemingly disparate elements in the Physics into a neat unitary stucture.' Canadian Philosophical Review