The paper reconstructs a late ancient debate concerning a dilemma raised by Aristotle's De Anima: How can an impassive soul account for perceiving qua being affected by perceptual objects? It is argued that Alexander and Themistius developed radically different approaches which can be better understood within a larger context of the dialogue between Aristotelianism and Platonism. The debate is shown to be instructive in underlining difficulties inherent in Aristotle's account.