Plato and Aristotle. Two ontologies in contrast

The purpose of this paper is to put forward two theses on the nature of metaphysics and its object in Aristotelian thought, which assume and simultaneously render the irreducibility of Platonic and Aristotelian ontology evident. Through the introduction and discussion of these theses, it will be made clear that the substance is not an operative, or merely taxonomical notion, but always has an invariant ontological content in Aristotle’s philosophy. We will find that the irreconcilable difference between the Platonic and Aristotelian ontologies stems precisely from this content.