Aristotle's "Physics Book 3" covers two subjects: the definition of change and the finitude of the universe. Change enters into the very definition of nature as an internal source of change. Change receives two definitions in chapters 1 and 2, as involving the actualisation of the potential or of the changeable. Alexander of Aphrodisias is reported as thinking that the second version is designed to show that Book 3, like Book 5, means to disqualify change in relations from being genuine change. Aristotle's successor Theophrastus, we are told, and Simplicius himself, prefer to admit relational change. Chapter 3 introduces a general causal principle that the activity of the agent causing change is in the patient undergoing change, and that the causing and undergoing are to be counted as only one activity, however different in definition. Simplicius points out that this paves the way for Aristotle's God who moves the heavens, while admitting no motion in himself. It is also the basis of Aristotle's doctrine, central to Neoplatonism, that intellect is one with the objects it contemplates. In defending Aristotle's claim that the universe is spatially finite, Simplicius has to meet Archytas' question, "What happens at the edge?". He replies that, given Aristotle's definition of place, there is nothing, rather than an empty place, beyond the furthest stars, and one cannot stretch one's hand into nothing, nor be prevented by nothing. But why is Aristotle's beginningless universe not temporally infinite? Simplicius answers that the past years no longer exist, so one never has in infinite collection.

In the sixth century AD Simplicius produced detailed commentaries on several of the works of Aristotle, which help in our understanding of the "Physics", and of its interpretation in the ancient world. This is Urmson's translation of Simplicius' commentaries on "Physics 5" in which Aristotle lays down some of the principles of his dynamics and theory of change. What does not count as a change: change of relation?; the flux of time? There is no change of change, yet acceleration is recognized. Aristotle defines "continuous", "contact" and "next", and uses these definitions in discussing when we can claim that the same change or event is still going on.

Simplicius and Priscian were two of the seven Neoplatonists who left Athens when the Christian Emperor Justinian closed the pagan school there in AD 529. Their commentaries on works on sense perception, one by Aristotle and one by his successor Theophrastus, are translated here in one volume. Both commentaries give a highly Neoplatonized reading to their Aristotelian subjects and give an insight into late Neoplatonist psychology.

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.

Aristotle's "Physics "Book 3 covers two subjects: the definition of change and the finitude of the universe. Change enters into the very definition of nature as an internal source of change. Change receives two definitions in chapters 1 and 2, as involving the actualisation of the potential or of the changeable. Alexander of Aphrodisias is reported as thinking that the second version is designed to show that Book 3, like Book 5, means to disqualify change in relations from being genuine change. Aristotle's successor Theophrastus, we are told, and Simplicius himself, prefer to admit relational change. Chapter 3 introduces a general causal principle that the activity of the agent causing change is in the patient undergoing change, and that the causing and undergoing are to be counted as only one activity, however different in definition. Simplicius points out that this paves the way for Aristotle's God who moves the heavens, while admitting no motion in himself. It is also the basis of Aristotle's doctrine, central to Neoplatonism, that intellect is one with the objects it contemplates.In defending Aristotle's claim that the universe is spatially finite, Simplicius has to meet Archytas' question, "What happens at the edge?." He replies that, given Aristotle's definition of place, there is nothing, rather than an empty place, beyond the furthest stars, and one cannot stretch one's hand into nothing, nor be prevented by nothing. But why is Aristotle's beginningless universe not temporally infinite? Simplicius answers that the past years no longer exist, so one never has an infinite collection.