Gad Freudenthal offers an original new account of one of Aristotle's central doctrines, his theory of material substance. Freudenthal argues that Aristotle's concept of heat is a crucial but hitherto ignored part of this account. Aristotle's 'canonical', four-element theory of matter fails to explain the coming-to-be of material substances (the way matter becomes organized) and their persistence (why substances do not disintegrate into their components). Interpreters have highlighted Aristotle's claim that soul is the active cause of the coming-to-be and persistence of living beings. On the basis of dispersed remarks in Aristotle's writings Freudenthal argues that Aristotle in parallel also draws on a comprehensive 'naturalistic' theory, which accounts for material persistence through the concepts of heat, specifically vital heat, and connate pneuma. This theory, which bears also on the higher soul-functions, is central in Aristotle's understanding of the relationship between matter and form, body and soul. Dr Freudenthal aims not only to recover this theory and to highlight its explanatory roles, but also to make suggestions concerning its origin in Presocratic thought and in Aristotle's own early theology. He further offers a brief review of how later ages came to grips with the difficulties inherent in the received version of Aristotle's matter theory. This book is an important contribution to the proper understanding of a central Aristotelian doctrine, which straddles 'chemistry', biology, the theory of soul, and metaphysics. 'This bold and vigorous study contributes greatly to the growing body of work on the essential connections between Aristotle's biology and central issues in his metaphysics and psychology . . . Comprehensive and lucidly argued, this book is strongly recommended for all university and college libraries.' Choice 'The book offers a new and refreshing description of Aristotle's system and demonstrates that without understanding the basics of Aristotle's biology, his conception of the structure of the physical world cannot be fully understood. The book is carefully and thoughtfully outlined and very well written. For quite a while I have not read a book that contributed so much to my understanding of Aristotle.' Early Science and Medicine