Theory of Forms
On Ideas (Greek: Περὶ Ἰδεῶν, "Peri Ideōn") is a philosophical work which deals with the problem of universals with regards to Plato's Theory of Forms. The work is supposedly by Aristotle, but there is not universal agreement on this point. It only survives now as fragments in quotations by Alexander of Aphrodisias in his commentary of Aristotle's "Metaphysics".