ABSTRACT
Obviously, one cannot do justice even to a few parts of Aquinas’s metaphysics in a single chapter,1 but I want to lay out roughly here the main elements of what might be called ‘Aquinas’s theory of things’. This is not the same as his ontology or his theory of what there is in the world, since he supposes that being – what there is – is spread over all the ten Aristotelian categories and not just the category of substance, which includes things. It is not the same as his theory of substance either, however, since it is arguable that not everything he recognizes as a thing counts for him as a substance.2 For the purposes of this chapter, I will take things to include not only substances and artifacts but also at least some of the parts of which substances are constituted. By ‘parts’ in this context, I mean both what Aquinas called ‘integral parts’, such as the hand of a human being or the roof of a house, and also metaphysical parts, such as matter and form, which constitute material things in a way different from the way they are constituted by their integral parts.3 In order to understand Aquinas’s basic worldview, it is important to understand his theory of things, and especially his view of what it is for something to be one thing.
