Thomas Seissl (University of Vienna): Why does Aristotle say that all change is continuous?

Despite all interpretative difficulties, it is fairly clear that one main aim of Aristotle’s Physics deals with rejecting all forms of atomism―of space, time, movement. Thus, he holds that all changes happen continuously (Physics III.1, 200b16-18; IV.11, 219a12-13; VI.4, 234b10 et passim), i.e. are infinitely divisible. The issue of how this Aristotelian claim can be justified is quite in disagreement among interpreters. Aristotle, overtly, proposes two strategies to overcome the Atomistic challenge: in Physics III-IV, he argues that the continuity of time and change can be explained by appeal to the continuity of magnitude; in Physics VI, arguing for the continuity of change, in contrast, is warranted by the continuity of the changing thing’s body. Curiously enough, Aristotle seems to accept the possibility of discontinuous changes in at least two passages in the Physics (I.3, 186a13- 16; VIII.3, 253b23-26) and one passage in De sensu 6 (446b28-447a3). In all of these three passages, he introduces the claim that some changes happen “at once”, “instantaneously” or “all together” (ἀθρόος). His prime example is freezing. This flatly contradicts his claim that all changes happen continuously.

In my paper, I shall argue that Aristotle’s line of argument actually operates with conflicting accounts of continuity in Physics III-IV and VI, since there are different notions of moving causes at work. On my interpretation, this conflict is only ruled out in Physics VIII Aristotle reassesses his strategy of explaining continuity. The recourse to Physics VIII has at least two advantages in my view: it, first, offers a framework which satisfies both approaches: continuity by magnitude and continuity by bodily extension. Second, it gives some insight on why Aristotle could speak about changes happening “at once”. This, in turn, appears plausible in view of Aristotle’s definition of change (Physics III.1, 201a10-11), or so I shall argue.

My paper proceeds as follows. The first section discusses Aristotle’s definition of change. From there, we shall have a look at the two different and mutually exclusive approaches to the claim that all changes are continuous. In the third section, I will recapitulate the results from the first section and show how, in my understanding, the continuity of change can be justified by integrating the approaches from the second section with appeal to Physics VIII. In an epilogue, I discuss how this issue is relevant in a dispute between Simplicius and John Philoponus. A result is that the Aristotelian concept of change is seemingly familiar to us, but differently motivated from questions raised in modern discussions.


This lecture will be given on Thu, 1 July 2021, 10:50 (UK time) as part of the workshop Change and Changemakers in Ancient Philosophy. The workshop is a collaborative initiative of the Change and Changemakers Network (Siegen) together with the Mereology of Potentiality Project (Oxford).