Understanding the metaphysics of properties, the building blocks of ancient ontologies, is foundational to understanding ancient philosophy.

This Element provides an overview of how the ancient thinkers (Anaxagoras, Plato and Aristotle) theorised about properties; such overview puts in relief the inquiries, problems and solutions they were pursuing while engaged in dialogue with each other. It examines alternative philosophical perspectives existing in antiquity concerning the explanation of property qualification, qualitative similarity, compositeness, and oneness. It further argues that although Plato was the first to conceptualise recurring universals, he did not reify them and did not admit them in his ontology; it was Aristotle who did, and developed his metaphysics around them. Aristotle, building on Plato's work, identified the metaphysical phenomenon of the instantiation of properties and developed an account for it. Finally, this Element outlines Aristotle's 'sophisticated' account of the oneness of a substance and argues that it was not hylomorphic.