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 composition of what-is (quod est) and being (esse). It argues that this distinction describes a composition of a concrete subsisting thing, susceptible of accidents, with its own being-in-act-what-it-is (esse substantiale in actu). While it has been common in modern scholarship to view Thomas as only nominally indebted to Boethius, but more profoundly indebted to Avicenna for this doctrine, this dissertation, drawing on a fresh consideration of Thomas’s sources and texts, argues that the reverse is the case. Thomas happily incorporates the Avicennian language of a quiddity/essence-esse composition in created intellectual substances into his own works, but he transforms the content of this Avicennian distinction to better align with the traditional Boethian doctrine of a composition of concrete subject with its own being-what-it-is (esse aliquid in eo quod est). Included within this dissertation is a new interpretation of the phrases “substantial being” (esse substantiale) and “act of [a] being” (actus essendi / entis); of the logic of predication; of the meaning of the question, “Does it exist?” (an est); and of Thomas’s principal arguments for the real composition of quod est and esse.

Ch. 0: Introduction and Literature Review 

Ch. 1: Avicenna, Alfarabi, and Averroes 

Ch. 2: Boethius and William of Auvergne 

Ch. 3: Thomas’s Averroistic Critique of Avicenna 

Ch. 4: The Logic of Actus entis 

Ch. 5: Thomas Aquinas on the Accidentality and Actuality of Esse