This is the commentary attributed to Simplicius on Aristotle's "On the Soul". It is intended to provide a wider readership with the opportunity to assess the disputed question of authorship. Is the work by Simplicius, or by his colleague Priscian, or by another commentator? The commentary is a source for late Neoplatonist theories of thought and sense perception and provides insight into this area of Aristotle's thought. In this volume the Neoplatonist commentator covers the first half of Aristotle's "On the Soul", comprising Aristotle's survey of his predecessors and his own rival account of the nature of the soul.