Abstract

Alexander of Aphrodisias, Aristotle’s commentator par excellence, rarely engages with Plato. In the present paper, however, we see him at work as an exegete of a passage in the _Phaedrus_ (245c5-9), in which Plato argues for the immortality of the soul based on its self-motion. In this paper, I focus on two ways in which Alexander deals with the passage. In his commentary on Aristotle’s _Prior Analytics_ (CAG II 1), Alexander employs the same approach to the _Phaedrus_ that he uses with Aristotle’s treatises: he puts an informal argument expressed in ordinary language into the more formal shape of a syllogism. This does not mean that Alexander gives his approval to Plato’s theory. In fact, in his commentary on Aristotle’s _Topics_ (CAG II 2), Alexander introduces a polemical discussion of the same Platonic argument. Commenting on Aristotle’s denial that the soul is a self-moving substance (_Top_. IV 1.120b21-29), Alexander spells out the implicit reference to the _Phaedrus_ and criticizes Plato’s argument for not taking into account the difference between an accidental property of the soul and the essential characteristics by which it is defined. Plato’s theory of self-motion is partly accepted by Alexander and partly criticized. This paves the way for how the theory will be applied in the Aristotelian tradition, not to the soul, as in Plato, but to the ensouled body, either of the living being or of the heavens.