Title: Aquinas the Boethian: Toward an Interpretation of Thomas's Quod est-Esse Distinction in Light of His Sources

This dissertation offers a reevaluation of the meaning of and sources for Thomas Aquinas’s doctrine of the distinction between essence and esse. At least since Pierre Duhem, it has been common to view Thomas as following William of Auvergne in reading the Avicennian distinction between quiddity and esse into the traditional Boethian formula of a distinction between quod est and esse. This dissertation argues that nearly the opposite is the case. When one considers Thomas’s technical vocabulary—for instance, “esse substantiale” and “actus entis”—in its proximate scholastic context as well as Thomas’s use of Averroes’s critique of Avicenna, it becomes clear that rather than reading an Avicennian doctrine into Boethian formulae, Thomas is, in fact, redirecting Avicennian formulae to what is substantially a Boethian doctrine.

Ch. 0: The Problem of the Accidentality and Essentiality of Being in Aquinas

Ch. 1: Avicenna, Alfarabi, and Averroes

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