The commentary attributed to Simplicius on Aristotle's On the Soul appears in this series in three volumes, of which this is the first. The translation provides the first opportunity for a wider readership to assess the disputed question of authorship. Is the work by Simplicius, or by his colleague Priscian, or by another commentator? In the second volume, Priscian's Paraphrase of Theophrastus on Sense Perception, which covers the same subject, will also be translated for comparison. Whatever its authorship, the commentary is a major source for late Neoplatonist theories of thought and sense perception and provides considerable insight into this important area of Aristotle's thought. In this first 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.

In On the Soul 3.1-5, Aristotle goes beyond the five sense to the general functions of sense perception, the imagination and the so-called active intellect, the of which was still a matter of controversy in the time of Thomas Aquinas. In his commentary on Aristotle's text, ‘Simplicius' insists that the intellect in question is not something transcendental but the human rational soul. He denies both Plotinus' view that a part of the soul has never descended from uninterrupted contemplation of the Platonic Forms, and Proclus' view that the soul cannot be changed in its substance through embodiment. He also denies that imagination sees things as true or false, which requires awareness of one's own cognitions. He thinks that imagination works by projecting imprints. In the case of mathematics, it can make the imprints more like shapes taken on during sense perception or more like concepts, which calls for lines without breadth. He acknowledges that Aristotle would not agree to reify these concepts as substances, but thinks of mathematical entities as mere abstractions. Addressing the vexed question of authorship, H. J. Blumenthal concludes that the commentary was written neither by Simplicius nor Priscian. In a novel interpretation, he suggests that if Priscian had any hand in this commentary, it might have been as editor of notes from Simplicius' lectures.