Abstract

There are two competing models for how to understand Aquinas’s hylomorphic theory of material substances: the Simple Model, according to which material substances are composed of prime matter and substantial form, and the Expanded Model, according to which material substances are composed of prime matter, substantial form, and all of their accidental forms. In this paper, I first explain the main differences between these two models and show how they situate Aquinas’s theory of material substances in two different places within the contemporary debate on concrete particulars, highlighting several advantages that Aquinas’s approach has over other varieties of substratum and bundle theory along the way. I then offer some reasons to think that the Expanded Model, as a theory of concrete particulars, is preferable. I argue that the Expanded Model avoids two major concerns for the Simple Model: the problem of extrinsicality, and the problem of too-many-possessors.