Date of Award

January 2017

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Kara Richardson


Aquinas, Hylomorphism, Soul, Substantial Unity

Subject Categories

Arts and Humanities


In this dissertation I examine Thomas Aquinas’ account of the metaphysical nature of the rational soul and its hylomorphic union with the body. Aquinas simultaneously holds that the rational soul is the substantial form of the human being and that it is an incorporeal subsisting thing that survives death. This particular pairing of views is notoriously difficult. On the one hand, Aquinas argues that because of the soul’s role as substantial form, it informs prime matter so as to compose a single unified substance—the human being. Unlike aggregates or accidental unities, the human being is something unqualifiedly one, that is, something unum simpliciter. On the other, his commitment to the incorporeity and subsistence of the soul as well as its continued exitence after death appear to threaten this unity—if the soul’s existence does not depend on the body, and it can exist on its own, then it seems to be a complete substance in its own right. If so, on Aquinas’ view, it cannot be united to anything else to form something unum simpliciter. So, in spite of Aquinas’ insistence that the human being is unqualifiedly one it is not clear that he is philosophically entitled to it.

In the first half of my dissertation I determine the extent to which the incorporeity, subsistence, and incorruptibility of the soul threaten to undermine Aquinas’ account of human unity. I argue that when his account of the soul and its relationship to the body is properly understood within his metaphysical framework, the metaphysical nature of the soul is compatible with human unqualified unity. Moreover, I argue that although human beings are metaphysically unique among created substances in his ontology, Aquinas adequately motivates their peculiar hybrid status.

In the second half of my dissertation, I discuss two of Aquinas’ arguments for the hylomorphic union of body and soul. Both arguments are found in Summa Theologiae I.76.1. The first is based on Aristotle’s demonstration in De Anima II.2 that the soul is the form of the body. I argue that while Aquinas’ version of the argument is similar to Aristotle’s in many ways, it goes beyond Aristotle’s in ways that reflect his specific motivations, and in particular, his disagreement with Averroes concerning the relationship between intellective soul and body.

The second argument for hylomorphism in Summa Theologiae I.76.1 involves Aquinas’ rejection of three competing accounts of the relationship between intellect and body, namely, the Platonist, Averroist, and Moved-Mover accounts. While Aquinas’ argument may initially appear to be a mere argument by elimination, I argue that a common theme emerges in his rejection of the alternatives. According to Aquinas, none of his competitors can satisfactorily account for the rationality, animality, and unity of the human being. At best, each competitor can account for two out of the three. In his view, therefore, Aquinas’ rejection of competing accounts provides positive reasons for affirming the hylomorphic account of body and soul, namely, that only his view can succeed where the others fail.


Open Access