Aristotle on time: A Study of the Physics (review)

It is 10:01 a.m. In a moment, it will be 10:02, and so on. Time moves steadily onward, transforming the future into present moments and, eventually, relegating them to the fixed past. Clocks may lag, some moments drag while others pass by in a flash, but we tend to hold the substantival belief that time exists independently of our perception of it, and of the events that take place in it. Aristotle understood time quite differently, defining it as "a number of motion [kinêsis] with respect to the before and after" (Phys. 219b1-2). But this definition has been criticized as being inescapably circular on the ground that the terms in the definiens are themselves temporal. Roark's Aristotle on Time, an elegantly conceived and concisely executed examination of the thorny last chapters of Phys. IV, aims to rescue Aristotle's account from the circularity charge by showing that Aristotle thought of time as a hylomorphic compound: motion is the matter (hulê) of time while perception is its form (morphê).

Roark's book is divided into four parts. Part 1 sets up the hylomorphic analysis by aiming to demonstrate Aristotle's indebtedness to Plato's account of time as the imposition of the appropriate form (number) upon the relevant raw material (motion). The unified project of Part 2 is to develop the material aspect of time, and ultimately to show that Aristotle had a distinctly kinetic sense of "before and after," which provides the basis for temporal order. For Roark, motion is "the actuality of what is potentially" (201a10 and b4), namely a telic property compound (or kinoumenon). Roark suggests that "before" and "after" denote "kinetic cuts," states of kinoumena specified in terms of spatial location: one kinetic cut is "before" another if the spatial interval specified in the latter is included in that specified by the former. This is a clever move, though I worry that the potentiality-actuality distinction, itself, can only be understood diachronically. While actuality is prior in substance to potentiality (Met. 1050b6-7), potentiality is prior in time: e.g. the embryo proceeds from the state of being a potential human to the state of being an actual human (Phys. 225b16-25).

Part 3 is devoted to the formal aspect of time: perception. Because time is an "evident proper feature of motion" (58), Roark needs to explain how perception (aisthêsis) creates temporal order. His view is that time is constituted by percipient acts, which "carve up" spatial magnitudes into determinate segments, which are then numbered (hence "time is a number of motion"). Since number is a common perceptible, the perception of which requires imagination (phantasia), phantasia is ultimately responsible for ordering kinetic cuts, and hence perceiving time. Though a bit of a digression from the main argument, chapter 9 (on the common perceptibles) shows how Roark's reading can be fruitfully applied to issues in Aristotle's moral psychology, such as akrasia. On Roark's view, the akratic is unable to resist present objects of desire because he cannot form counterfactual phantasms, and hence is unable to anticipate the negative consequences that will happen if he yields to temptation.

In Part 4, Roark uses the hylomorphic interpretation to address several potential problems for Aristotle's theory of time, such as simultaneity and temporal passage. Stylistically, it appears less unified with the first three parts, but Roark makes clear how the earlier analysis of time as an evident proper feature of motion forestalls worries about the "flow" of time by showing how "'time's arrow' is essentially a metaphysically gussied-up version of 'motion's arrow'" (210).

The great strength of Roark's book is its nuanced attentiveness to the way Aristotle did philosophy: Roark does not employ hylomorphism merely as a heuristic device, asking us to imagine time, analogically, as though it were a combination of matter and form. Rather, he elegantly shows that time, for Aristotle, like individual substances, really is "a variety...