William of Auvergne is the first of the great philosophical theologians of the thirteenth century; his thought is original, systematic, and vigorous. He was the first medieval theologian to take serious account of the Greek and Arab philosophical works that poured into the West during the last half of the twelfth and beginning of the thirteenth centuries. The translation of nearly all the Aristotelian works, along with those of Arab and Jewish philosophers and theologians, confronted the Christian West for the first time with a rival understanding of the world and of humanity and its destiny. Despite repeated ecclesiastical warnings against Aristotle's writings and Arabic thought in 1210, 1215, and 1231, William continued to study Avicenna and used his metaphysics and psychology to come to an understanding of the Christian faith. Though William rejected the doctrine of Aristotle and Avicenna when it opposed the faith, he used it and expounded it...