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. Proclus is able to see lucidly the differences between antiquity’s greatest philosophers without resorting to some form of mental acrobatics to create an agreement, as for instance Simplicius is sometimes fond of doing. The differences in the Neoplatonists’ views on the relationship between Plato and Aristotle are of a fundamental character and thus should not be characterised as mere ‘details’ (Gerson Reference Gerson2005: 16) or ‘nuances’ (Hadot Reference Hadot1992: 421).Footnote ¹

(2) Nevertheless, Proclus still believes that in some areas there is an agreement between the two philosophers. In the case of Elements of Physics, I have shown in Chapter 1 that Proclus exhibits a detailed knowledge of Aristotle’s natural philosophy which he seems to endorse to a certain degree. Concepts such as the existence of three simple natural motions and the finitude of bodies are endorsed, just as the idea that bodies have only a finite power. He likewise accepts the notion of an unmoved mover as ultimate origin of motion. His explanations, however, differ: in EP he takes over Aristotle’s arguments (Section 2.5.1), while in Elements of Theology and other works he provides a different, Platonist reasoning (Sections 2.5.2–3). Obviously, the latter account is in Proclus’ mind more fundamental since it is grounded in general metaphysical laws. Interestingly, this does not imply that Proclus actually views the unmoved mover as genuinely Aristotelian, as I clarified in Chapter 2: rather he regards the philosophical parentage of this entity as Platonic. This is part of a common Platonist methodology of backdating Aristotelian and generally later philosophical insights to Plato. The same applies to the case of the prime mover’s causality, as shown in Chapter 4. While Proclus shows that Aristotle’s premises ultimately force him to accept it as efficient cause of the cosmos’ being, he also provides his own philosophical and exegetical reasons – based on Plato – to accept this view. Regarding the soul’s self-motion and extension, Proclus again seems to entertain the idea of an agreement between Plato and Aristotle, since both deny that the soul is extended in space and has physical motion (see Chapter 3). Here, Aristotle’s criticism of a literal understanding of the psychogonia serves a constructive function, as it shows Proclus how absurd it is to understand the soul as extended and moving in space.

Since Proclus grounds (what to us modern interpreters appear to be) Aristotelian doctrines – such as the intellect as prime mover and final cause or self-motion as non-spatial – in his exegesis of Plato, he leaves the impression that already Plato held these views and belittles the influence Aristotle actually had on the development of such positions. Consequently, Proclus appears in our eyes to be more Aristotelian than he himself was aware of. All in all, the picture of Aristotle’s agreement with Plato, as entertained by Proclus, is one marked by Aristotle’s inferiority due to Plato’s superior role in providing a stronger argumentative and exegetical background. Nevertheless, Proclus deems the study of Aristotle useful and, in fact, indispensable, because of the details he provides in his investigation of, for example, natural philosophy. This fits well with the view of Aristotle’s works as ‘lesser mysteries’ intended for preparing students to be initiated in the ‘mystagogy’ of Plato’s dialogues.Footnote ²

(3) In interpreting Aristotle, Proclus is part of a common exegetical tradition with which he engages – be that in some of the terminology he uses in EP, which he shares with Simplicius and earlier exegetes (Sections 1.2.2 & 1.3.3.1), or in the way he construes Aristotle’s argument for the prime mover’s efficient causality, which is inspired by Syrianus (Section 4.3.3.4). However, he also deviates from it where he sees fit. As I demonstrated in Chapter 1, Proclus changes the common order of discussing Aristotle’s Physics and De caelo by starting with De caelo 1 and then presenting the material from Physics 8. Interestingly, he also excludes material from these books due to the possible conflict with Plato. Regarding his critique of Aristotle’s metaphysics, I have tentatively argued that he goes further than Syrianus.

(4) Importantly, Proclus deals with Aristotle’s criticism of Plato differently from other Neoplatonists such as Ammonius and his pupils, as I was able to show for the first time in a detailed discussion. Unlike these philosophers, Proclus believes that Aristotle’s intention was to attack Plato directly and to refute his views, as became clear in my discussion of Proclus’ rebuttal of Aristotle’s objections to the Timaean cosmogonia (Section 1.2.3.2) and psychogonia (Section 3.4.2). At some point, Proclus even points out that Aristotle’s criticism can be harmful, if taken at face value, as it distorts our understanding of Plato (see Section 1.2.3.2 n. 52). Again, Proclus’ position appears more persuasive than, for instance, Simplicius’, considering that no serious scholar nowadays would doubt that Aristotle actually wanted to attack Plato in De anima 1.3, De caelo 1.10–12 or Metaphysics 1.6. His interest in refuting Aristotle’s objections is stronger than in other Neoplatonists, as is emphasised by the two monographs, Investigation of Aristotle’s Objections to the Timaeus and Investigation of Aristotle’s Objections to the Republic, he dedicated to them.

(5) I have also demonstrated that Proclus’ engagement with Aristotle’s objections to Plato also differs from the approaches of the Middle Platonists: Proclus engages in a productive way with these criticisms and takes them more seriously than the Middle Platonists. This is evidenced by three theses accepted by some Middle Platonists but rejected by Aristotle and the Neoplatonists:

1. (i) The cosmos is generated (in time) and indestructible (Chapter 1).

2. (ii) Unmoved mover and self-mover are principles of motion (Chapter 2).

3. (iii) Soul has a spatial/physical motion (Chapter 3).

Theses (i) and (iii) are held by Plutarch and Atticus, (ii) by Alcinous. I argue that the Neoplatonists’ rejection of these three theses is to a significant degree influenced by their reading of Aristotle. This is evident from their citations or even exegeses of these Aristotelian passages. This, in turn, is accounted for by the higher authority that the Neoplatonists ascribed to Aristotle: these philosophers interpret Plato by bearing in mind Aristotle’s criticisms, which then leads to making Plato immune to these objections. Thus, unlike certain Middle Platonists, they hold the view that, according to Plato,

1. (i) The cosmos is indestructible and not generated in time.

2. (ii) The unmoved intellect is the ultimate origin of motion; soul is only an intermediary principle of motion.

3. (iii) Soul has a non-spatial/non-physical motion.

These doctrinal differences emphasise the fecundity of Aristotle’s objections for the development of Neoplatonism in general and Proclean thought more specifically, as the engagement with Aristotelian and Middle Platonist views emerges most clearly in the latter.

(6) Lastly, I have illustrated how certain Aristotelian and Platonic texts had a formative influence for Proclus’ views. In the case of EP, I argued that Aristotle’s Posterior Analytics shaped Proclus’ views on axiomatics more than previously assumed and how this helps us understand why Proclus structured EP in the way he did (Sections 1.3.2–3). In arguing for the existence of the prime mover and its causality, he makes generous use of De caelo1, Metaphysics 12 and Physics 8 and partly transforms their arguments (Chapters 1; 2; 4). Likewise, in his discussion of soul’s self-motion and the conditions of its immortality, he takes over Aristotelian arguments from De anima, such as soul’s lack of spatial extension and separability from the body. In regard to Plato’s dialogues, I demonstrated in Chapter 3 (especially 3.4.3) the significance of Laws 10 for the Neoplatonist theory of motion, especially self-motion. For the future a more thorough examination of the dialogue’s influence among these philosophers remains highly desirable.

In summary, I have shown that Proclus and other Neoplatonists engaged with serious problems in Plato and Aristotle that yet remain to be solved by modern scholarship. Many of our seemingly recent debates are prefigured by the Neoplatonist discussions, and Proclus’ interpretations certainly help us better understand these disputes. In spite of what appears to be an arcane metaphysics, Proclus is able to systematise significant insights from Plato and Aristotle and to offer a unified philosophical worldview that is often sensitive to the concerns of these philosophers. My study allows for further research in the reception of Aristotle in Proclus by considering other pertinent topics such as causality or psychology that have been discussed here only in regard to their relevance for his concept of motion. Crucially, it shows that studying the Platonist reception of Aristotle’s criticism of Plato is indeed an integral part of understanding Proclus’ thought.