Abstract

Aristotelians traditionally motivate the doctrine of first (“prime”) matter by claiming that substantial change requires a subject. Without gainsaying that motivation, I propose another: first matter is a necessary postulate for the sort of unity proper to a substance. This motivation arises if one examines a claim that Patrick Toner and Robert Koons share: (TM′) the possession of emergent causal powers is necessary for substancehood. I first explain how TM′ represents the application of “Merricks’s Dictum” (“For a macrophysical object to exist is to have causal powers”) to an Aristotelian framework. Next, I argue that, as Toner’s and Koons’s respective theories use TM′, it is incompatible with the denial that substances have substances as proper parts. In Toner’s hylomorphism, TM′ entails that an entity’s matter and form are independent substances. As part of Koons’s theory, TM′ implies that an entity’s elementary parts are substances. Happily, a hylomorphist need not accept TM′. For example, Aquinas rejects TM′ as incompatible with the doctrine of first matter. An ontology like Aquinas’s that includes first matter navigates the dialectical straight between the dualism and atomism. If she commits to first matter, the hylomorphist can deny that substances have substances as proper parts.