Etienne Gilson published six editions of his book devoted to the philosophy of Thomas Aquinas. The appearance of these editions, the first in 1917 and the last in 1965, covers much of the scholarly life of their author. As he says in his Preface, the book was his lifelong companion. The editions represent a sustained effort to set forth his developing views on the philosophy of the man who, in Gilson's opinion, most profoundly sought out the heart of reality: being, understood as the act of existing (esse). Gilson presents his thoughts on this subject with new clarity and precision in his revised sixth and final edition, which is here put into English for the first time. While probing into Thomas's philosophy, Gilson measures it against the views of his predecessors: notably Plato, Aristotle, Plotinus, and the Pseudo-Dionysius among the Greeks, and Avicenna and Averroes in the Islamic world. Among the Latins, he pays particular attention to the views of Augustine, Boethius, Anselm, and in his own century to those of Alexander of Hales and Bonaventure. Gilson sees Aquinas as retrieving much of the long tradition of philosophy in which he was schooled, but surpassing it with his original insights and developments. Most important, in Gilson's opinion, is that Thomas goes beyond the essentialist ontology bequeathed to the Middle Ages by Augustine, among others, and reaches a 'new ontology' which is truly existential. With this leitmotif, in Part 1 Gilson explores Thomas's notions of the existence and nature of God and our access to them. Part 2 examines the emanation of the world from God and the hierarchy of creatures, culminating in the human person. Part 3 contains Gilson's fullest treatment of Thomas's moral doctrine, featuring the human act, its principles, and the personal, social, and religious life. While stressing the strictly rational character of Thomistic philosophy in the way it reaches its conclusions, this edition, like its predecessors, emphasize its development within Thomas's theology and the guidance it receives from the Christian faith. Language : English.