Abstract

The paper presents a general reconstruction of Aquinas’s interpretation of Aristotle’s Metaphysics, Book Z, the book devoted to the notion of substance. The aim of the study is to evaluate Aquinas’s reading in the light of a series of exegetical and philosophical issues debated in the contemporary literature on Book Z. Therefore, the paper focuses on four main issues: the relation between Book Z’s ontology and the one outlined by Aristotle in the Categories; the problem of the definition of sensible substances; the question as to whether a thing is identical with its own essence; the ontological status of the forms of sensible substances. The paper presents Aquinas’s position on each of the aforementioned topics. The main thesis defended throughout is that Aquinas’s interpretation of Book Z is guided by the intuition that sensible substances are ontologically prior to their substantial components, matter and form.