Humboldt-Universität zu Berlin - Department of Philosophy - Philosophy, Science and the Sciences

Kίνησις.

The Structure of Motion in Aristotle’s Physics VIII

The main subject of Aristotle’s investigation of the physical world is nature (φύσις), which is described as “a principle of motion and change” (ἀρχὴ κινήσεως καὶ μεταβολῆς). Therefore, motion (κίνησις) becomes a crucial concept, discussed in different sections of the Corpus and examined thoroughly in Phys. III and VIII. Both these books carefully investigate motion from different points of view.

In Phys. III 1 Aristotle provides a complex definition of motion, which is defined as “the fulfillment of what is potential, as such” (201a10-11: ἡ τοῦ δυνάμει ὄντος ἐντελέχεια, ᾗ τοιοῦτον). This definition allows very different readings for each of its terms and opens the discussion on what “as such” means, or what the relationship between motion and the moving things is since Aristotle himself claims that “there is no such thing as motion over and above the things”. Most of these questions have been raised by the ancient commentators, who have also tackled the problem of how to define the terms actuality (ἐντελέχεια) and potentiality (δύναμις), which are still subject to an extensive debate. In the subsequent book, Phys. IV, Aristotle makes the puzzle even more complicated, by tying motion and its mechanism to other concepts, such as time and the continuum, as modern literature has highlighted.

In Phys. VIII Aristotle focuses primarily on the eternity of motion and the search for its ultimate cause (the so-called “Unmoved mover”). The central chapters of this book (4, 5, 6) are dedicated to the investigation of the things that move (κινεῖ) and are moved (κινεῖται) in the physical world in different ways (καθ' αὑτά and κατὰ συμβεβηκὸς) and to motion’s causal structure in living beings. The peculiar characteristic of the central chapters is that they address motion not from the point of view of its definition, but precisely from its structure, of how it takes place in physical reality, and how it occurs in the cosmos.

In this research, I will focus entirely on some sections of book VIII, since my main purpose is to provide a complete survey of Aristotle’s structure of motion and its dynamics. Of the whole book, I will provide a full-fledged analysis of the central chapters mentioned above. I shall use book III only as a starting point of my investigation in the light of what seems to be the aim of Aristotle in book III, namely, to describe motion as a process that is “in-between” potentiality and actuality. In detail, I will consider only the sections of Phys. III, close to the well-known definition, to show that two key terms in the analysis of motion, “the mover” and “the movable” – the ‘active’ and ‘passive’ parts of motion – play a role both in Phys. III and Phys. VIII. Since the secondary literature on the topic has not focused enough on this peculiarity, I aim to provide a thorough investigation. 

The main purpose of this study is to identify the causal structure of motion, on which physics and metaphysics collide. I will, however, occasionally refer to Plato: although Aristotle’s concept of motion is very different from Plato’s, there are some interesting points of reflection about what is moved and the mover (what imparts motion). The latter plays especially a crucial role in both Plato and Aristotle in different contexts and different forms, but the puzzle is about its nature. In Phys. VIII, Aristotle comes up with the demonstration of the ultimate cause of motion, the Unmoved mover, through a critical discussion of the Platonic theory of the self-motion of the cosmic Soul (illustrated mainly in Phaedrus, Timaeus, and Laws X). However, Aristotle himself seems to take into account Plato’s theory (see Phys. VIII, 5), for the idea of placing the principle of motion (ἀρχὴ κινήσεως) of the natural substances within them, suggests that each of them can be considered a ‘self-mover’ (Phys. VIII clarifies this point).

Within this research, I will also include some reflections on the differences between the study of motion in modern and contemporary philosophy of physics and Aristotle’s theory. It is undoubtedly true that Aristotelian physics has been overcome, but it is not necessarily true that the method of research adopted by Aristotle is overcome too and that some of the concepts used cannot play, at least conceptually, an explanatory role. My attention in this regard will be focused on the metaphysical concepts of agency and causality and their re-elaboration in contemporary terms.

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Contact: giulia.clabassi@hu-berlin.de