In the third chapter, I focus on the concept of self-motion, which is tied to the definition of soul in Plato. Aristotle famously criticises this view in De anima 1.3, showing that the soul is unmoved. I offer the first lengthy discussion of Proclus’ repudiation of Aristotle’s criticism which differs from other Neoplatonist responses. Most importantly, I demonstrate how Proclus develops his own views on self-motion by using Platonic and Aristotelian insights.

The first chapter deals with Proclus’ little studied treatise Elements of Physics where he sums up in an axiomatic manner Aristotle’s theory of motion from Physics VI, VIII and De caelo I. I demonstrate that Proclus’ project is embedded in an exegetical tradition and show how he omits certain parts of Aristotle’s works that might conflict with his Neoplatonist views. Additionally, I provide evidence for the view that Aristotle’s Posterior Analytics proved to be influential for the axiomatic structure of Proclus’ treatise.

The second chapter concerns the origin of motion in the universe. While Plato assumes a self-moving soul as origin, Aristotle posits an unmoved intellect. Proclus brings these two views together by regarding the unmoved intellect as ultimate source of motion and the self-moving soul as an intermediary entity. I demonstrate that his harmonisation effort goes beyond previous Platonist attempts due to the philosophical reasoning he provides. I also defend Proclus’ assumption of both unmoved intellect and self-moving soul as sources of motion against concerns brought up in scholarship.

The goal of this study was to offer a wide-ranging treatment of Proclus’ engagement with Aristotle and his criticism of Plato by focusing on the concept of motion. Thematically, my results can be summed up in six areas.

(1) My main conclusion is that Proclus does not share the view of an essential agreement between Aristotle and Plato – contrary to what is sometimes assumed in scholarship. This emerges most clearly in Proclus’ discussion of Aristotle’s metaphysical system and specifically Aristotle’s rejection of the One as well as deficient understanding of the intellect’s causality (Chapter 4). Proclus regards Aristotle as a defective imitator and epigone of Plato. Aristotelian and Platonic metaphysics do not agree on the types of principles they recognise. As I argued, Proclus’ interpretation of Aristotelian metaphysics is more sensible than Ammonius’ et al. who vainly strive to find the Aristotelian equivalent to the Platonic One. Crucially, this insight has implications for the historiography of late antique philosophy: not all post-Porphyrian Neoplatonists adhere to the harmony-doctrine.

The fourth chapter examines the problem of the causality of the unmoved mover. This issue is central in scholarship on Aristotle and goes back to late antiquity. I argue that here Proclus’ non-harmonist stance towards Aristotle emerges most strongly: not only did Aristotle fail to make the intellect an efficient cause of the cosmos’ being but his metaphysics generally is deficient, since he did not recognise the Platonic One as the highest principle. I contrast Proclus’ view with the position of Ammonius and Simplicius who see a complete agreement between Plato and Aristotle.

In this introduction, I outline Proclus’ relationship with Aristotle and provide an overview of the state of the art. I discuss Proclus’ views on the so-called harmony of Plato and Aristotle and contrast it with the views of other, contemporary Neoplatonists, showing that Proclus stands out as more critical of Aristotle. I show that the concept of motion provides a perfect avenue for understanding how Proclus sees the tension between Plato and Aristotle. Lastly, I explain how Proclus differentiates distinct levels of motion which also structure my discussion in the monograph.