The ten essays in this collection approach the philosophy of Thomas Aquinas not merely as an object of scholarly interest but also as a framework for addressing perennial philosophical questions, even as they are raised and debated in our own times. The first five articles are expositions of important philosophical themes as developed in Aquinas's own works. In the last five, the authors bring Aquinas's thought to bear on contemporary philosophical discussions of metaphysical, ethical, and social issues. In the first essay, Kenneth L. Schmitz explores the centrality of esse in Aquinas's thought and shows the richness of this notion by chronicling the changing currents in its study over the course of this century. Next, Jorge J.E. Gracia describes Aquinas's distinctive solution to the age-old problem of the ontological status of universals. Turning to ethical themes, David M. Gallagher outlines the precise nature of moral goodness and how Thomas relates it to his metaphysical understanding of the good. Gregory Martin Reichberg takes up the more specific issue of the possibility and nature of moral responsibility within the activity of theoretical or speculative thought. In the final essay of the first part, Edward P. Mahoney examines Aquinas's arguments against Averroes' doctrine of the unity of the intellect in order to show the consistency of Aquinas's teaching throughout his career. Beginning the second set of articles, Oliva Blanchette contrasts Thomas's notion of perfection with that of Charles Hartshorne, demonstrating how Hartshorne arrives at his particular understanding of the divine perfection. Alejandro Llano argues that the understanding of possibility employed by Jaako Hintikka and Simo Knuuttila is much narrower than Aquinas's analogical understanding, and that consequently they do not distinguish between logical and ontological possibilities. Turning to political philosophy, John P. Hittinger examines Jacques Maritain and Yves Simon's Thomistically inspired arguments for the desirability of modern liberal democracies, while questioning their consistency with Thomas's own political thought. Arguments that could have direct bearing on questions in medical ethics are examined in William A. Wallace's essay, in which he appeals to principles of Thomistic natural philosophy to argue that personal death may well precede the biological death of the human body. In the final article, Stephen F. Brown shows how Henry of Ghent rejected Thomas's understanding of theology's relationship to all lower sciences.