In this dissertation, I argue for the philosophical consistency of Aquinas’ hybrid view of human souls - that is, the idea that human souls, and only human souls, are at once substantial forms and subsistent things. I contend that the best way to understand the ontological status of human souls according to Aquinas is by means of the concept of ‘subsistent parts’. Since Aquinas characterizes souls as parts of substances, I propose a mereological analysis of the different types of part in Aquinas, and I conclude that souls should be seen as metaphysical parts of substances. An influential contemporary view holds that Aquinas’ doctrine is inconsistent on the grounds that nothing could be an abstract (form) and a concrete (subsistent) at the same time. I respond to this view by denying the widespread notion that substantial forms are purely abstract entities. I hold that the best way to make sense of Aquinas’ twofold approach to human souls is by saying that substantial forms possess an element of concreteness which is accounted for by the fundamental relationship between form and being. Finally, I address the question of taxonomy: how can we classify Aquinas’ view of the soul-body relation in light of the concepts that are currently used in philosophy of mind. I argue that the notion of a subsistent part entails the concept of ‘part-dualism’, which I present as standing midway between substance-dualism and nonreductive materialism, and also as being ontologically richer than property-dualism. I conclude this dissertation with a refutation of the idea championed by some prominent scholars that the existence of the soul is sufficient for the existence of the person.

In this dissertation, I argue for the philosophical consistency of Aquinas’ hybrid view of human souls - that is, the idea that human souls, and only human souls, are at once substantial forms and subsistent things. I contend that the best way to understand the ontological status of human souls according to Aquinas is by means of the concept of ‘subsistent parts’. Since Aquinas characterizes souls as parts of substances, I propose a mereological analysis of the different types of part in Aquinas, and I conclude that souls should be seen as metaphysical parts of substances. An influential contemporary view holds that Aquinas’ doctrine is inconsistent on the grounds that nothing could be an abstract (form) and a concrete (subsistent) at the same time. I respond to this view by denying the widespread notion that substantial forms are purely abstract entities. I hold that the best way to make sense of Aquinas’ twofold approach to human souls is by saying that substantial forms possess an element of concreteness which is accounted for by the fundamental relationship between form and being. Finally, I address the question of taxonomy: how can we classify Aquinas’ view of the soul-body relation in light of the concepts that are currently used in philosophy of mind. I argue that the notion of a subsistent part entails the concept of ‘part-dualism’, which I present as standing midway between substance-dualism and nonreductive materialism, and also as being ontologically richer than property-dualism. I conclude this dissertation with a refutation of the idea championed by some prominent scholars that the existence of the soul is sufficient for the existence of the person.