Abstract

It is well known that Thomas Aquinas's distinction between quod est and esse in all creatures is foundational to both his metaphysics and theology. It is also well known that he attributes this distinction to Boethius. In the twentieth century, however, many commentators came to view the true source for this distinction as Avicenna, not Boethius. Thus, they saw Aquinas as following the likes of William of Auvergne in creatively reinterpreting Boethius in an Avicennian direction. This dissertation tests the accuracy of this thesis by reconstructing Avicenna's quiddity-esse distinction, on the one hand, and Boethius's quod est-esse distinction, on the other, and by comparing Aquinas's own doctrine to those of his two predecessors. The fundamental difference between Avicenna's doctrine and Boethius's, according to this dissertation, is that Avicenna intends to distinguish an abstract quiddity (e.g., equinity; humanity) from a non-quidditative being-necessary (necesse esse) or being-in-effect (esse in effectu) whereas Boethius intends to distinguish a concrete subsisting creature (e.g., Socrates; man) from its very being-what-it-is (e.g., being-Socrates; being-a-man). Via a study of Aquinas's appropriation of Averroes's critique of Avicenna, Aquinas's theory of predication in its medieval grammatical context, and Aquinas's arguments for the distinction between creatures and their esse, this dissertation concludes that St. Thomas's doctrine is more consistent with that of Boethius than that of Avicenna. It is not a distinction between an abstract essence (e.g., humanity; gabrielity) and a non-quidditative esse, but rather a distinction between a concrete creature (e.g., Socrates; man; Gabriel) and its very being-in-act-what-it-is (esse substantiale in actu). Going beyond Avicenna and Boethius, Aquinas incorporates the Aristotelian distinction between potency and act into his doctrine about the metaphysical composition of creatures. This dissertation argues that a sharp distinction must be drawn between Aquinas's rationale for using the phrase "actus essendi," which Aquinas uses for primarily grammatical reasons, rooted in the medieval theory of the substantive verb, and Aquinas's rationale for saying that all creatures are composed with their esse as out of potency and act. Aquinas provides several, complementary metaphysical reasons for viewing the esse composed with a creature as its act by various analogies of proportionality to form. These analogies are spelled out in the final chapter of this dissertation. OUTLINE: Ch. 0: Introduction and Previous Attempts to Explain the Accidentality and Essentiality of Being Ch. 1: Avicenna and Averroes on the Accidentality of "Being" Ch. 2: Boethius and William of Auvergne Ch. 3: Thomas's Identification of Esse with Esse substantiale Ch. 4: The Logic of Actus entis and the Substantive Verb Ch. 5: The Accidentality and Actuality of Being in Thomas Aquinas Ch. 6: Conclusion