This is the first work to draw on the four hundred years of transition from ancient Greek philosophy to the medieval philosophy of Islam and the West. During this period, philosophy was often written in the form of commentaries on the works of Plato and Aristotle. Many ideas wrongly credited to the Middle Ages derive from these centuries, such as that of impetus in dynamics and intentional objects in philosophy of mind. The later Neoplatonist commentators fought a losing battle with Christianity, but inadvertently made Aristotle acceptable to Christians by ascribing to him belief in a Creator God and human immortality. The commentators provide a panorama of up to a thousand years of Greek philosophy, much of which would otherwise be lost. They also serve as the missing link essential for understanding the subsequent history of Western philosophy. Volume 1 of this indispensable sourcebook deals with psychology, which for the Neoplatonist commentators was the gateway to metaphysics and theology. It was the subject on which Plato and Aristotle disagreed most, and on which the commentators went furthest beyond them in their search for synthesis. Ethics and religious practice fall naturally under psychology and are included in this volume. All sources appear in English translation and are carefully linked and cross-referenced by editorial comment and explanation. Bibliographies are provided throughout.