Aristotle’s Definition of Time

In his attempt to make sense of the nature of time, Aristotle turns to several observable factors, namely, movement (or motion), change, and number. By number, Aristotle means observable sequence in terms of ‘before’ and ‘after.’ Of course, for Aristotle number is count which means that one could have a sequence without a measure or count. For example, there could be a sequence of things, which are static (without motion) and a count could be performed when considering this sequence. Moreover, the ‘before’ and ‘after’ in this type of sequence would be in the counting of the sequence and not the sequence itself. Thus, number and movement in Aristotle’s definition of time are, in a sense, similar, or have closely related functions[1]. As Aristotle himself declares, “for time is just this—number of motion in respect of ‘before’ and ‘after.’ Hence time is not movement, but only movement in so far as it admits of enumeration.”[2] Moreover, number is that which is counted or that which is countable and is also that which we count.[3]

Regarding movement Aristotle details that time itself is not movement (motion). However, time is not independent of movement.[4] Here, as J. T. Fraser points out, Aristotle is suggesting “that time is either identical with motion or it is something closely related to it.”[5] Additionally, Aristotle restricts motion to three kinds: qualitative, quantitative, and local.[6]
Aristotle describes qualitative motion as a change from black to white, or a change from cold to hot. Quantitative motion is a change in size. For example, an increase in measurement—one’s getting taller as they grow from childhood to adulthood. Local motion is change in place. This would be the most basic form of motion for Aristotle.

With regard to changes occurring between black and white, this is “ a process of whitening and change from cold to hot is a process of heating, and these can readily be understood quantitatively as rates of whitening and rates of heating. Now time is a quantifiable change from ‘before’ to ‘after.’[7] Thus, the conclusion is Aristotle’s famous definition of time as the number of motion in respect of ‘before’ and ‘after.’ Aristotle’s definition of time not only involves motion but change as well. Moreover, Aristotle’s use of kinesis (motion) is quite broad and encompasses all changes except substantial generation. In fact, Aristotle sees time as an aspect of not only motion but change. Philip Turetzky elaborates on this by declaring,

Aristotle thinks of time as an aspect of change, and things change from something to something else. Before and after are thus formal elements of change distinct from change, rather than part of its definition. The before and after of change comprise the initial and final states of a modification of some magnitude, not just spatial magnitudes. Since change can occur between qualitites, between places, as growth and diminution, and as creation and destruction, it advances from a prior state, before the change, to a posterior state, after the change. So Aristotle thinks that because “before” and “after” apply to magnitude they apply to change, and because they apply to change they apply to time. [8]

Moreover, Aristotle details that “we perceive movement [change] and time together.”[9] The operative term in this assertion is perceive. We perceive movement and time together in that time is dependent upon the mind. Aristotle illustrates this idea by declaring that if a person is in darkness and is thwarted from perceiving motion, the mind will still have motion in it via thought. This thought is movement in the mind and thus time has elapsed based on this internal movement. Here, Aristotle is clearly declaring that if movement is not perceived by the mind in physical things (due to darkness or some other thing thwarting a mind’s perception), time continues to lapse since there is movement which takes place in some mind by the enumeration of thought.

The fact that some time is thought to have passed denotes that some movement has occurred in the mind. Thus, our inability to perceive movement in physical things does not necessarily negate time’s persistence to elapse due to movement in our mind. Therefore, for Aristotle, time is not independent of movement. Aristotle supports this idea by declaring, “ time is either movement or something that belongs to movement. Since then it is not movement, it must be the other.”[10]

There is in this definition a sense in which time is dependent on motion or movement. This movement is either in the mind (as when vision is thwarted by darkness) or in things which we perceive as moving. This sense of time dependency upon movement is delineated by Michael J. White in his article “Aristotle on ‘Time’ and ‘A Time.’ White declares, “Aristotle sees a very close connection between ‘process’ or motion (primarily locomotion, it seems) and time. Since time is not to be identified with motion, it must be some feature of motion (219a 9-10). It is clear that a conception of time as an ontologically independent ‘container’ of process is quite foreign to Aristotle’s thought; rather, time, or times, are in some way ontologically dependent on things in process.”[11] White’s commentary of Aristotle’s definition of time and motion is quite helpful in placing our finger on what Aristotle is asserting about their connection. However, several questions seem to arise.

If what Aristotle declares is correct, that time is some feature of motion and time is dependent upon some mind, then how can Aristotle account for instances in the sensible world where there is no motion and no minds to perceive? For instance, let us say we have a group of students in a given classroom for one hour participating in a philosophy class. Movement in the room between students, the professor, and the thoughts of the minds of the students, for Aristotle, would constitute that time is elapsing. However, once the class session has ended, the lights have been turned out and the room is now completely motionless (granting that there is not a clock on the wall for there to be motion in the room) and there are no minds in the room, does time elapse in the room? Aristotle would initially say no, there is no time in the room. In this sense (or situation), Aristotle is very much an idealist with his notion of time. It should be pointed out here that Aristotle would probably declare that there is the potential for one to check in with the room in the beginning and walk around (thus providing the needed motion) and at any point in this process, return to the room. So essentially there could still be time in the sense that there is potential countability in the room.

Summing up this section, Aristotle’s view of time, simply put, can be defined as a nonsubsistence (nonbeing) thing which inheres in quantifiable change (‘before’ and ‘after’) and is that which is numbered. For instance, using Aristotle’s exact definition, it can be elaborated upon as such—time is the number (in that it is countable) of movement (in that it inheres in motion) in respect of before and after (in that it is quantifiable change). However, perhaps Aristotle believes that time might be too basic to admit of definition and this is why he begins his discussion of time in an aporetic fashion.

[1] In fact, movement (or motion), change and number are in a sense all closely related in that they serve similar functions. In other words, there is a close and perhaps inseparable connection between these. This will be fleshed out as we examine each.
[2] 219a 22-25, 372.
[3] Ibid., 219b 5-10. This notion will be examined in greater detail a little later.
[4] 219a 1.
[5] J. T. Fraser, The Voices of Time, 2nd ed. (Amherst: The University of Massachusetts Press, 1981), 13.
[6] 226a
[7] Fraser., 13-14.
[8] Philip Turetzky, Time (New York: Routledge, 1998), 20.
[9] 219a 4-5.
[10] 219a 8-9.
[11] Michael J. White, “Aristotle on ‘Time’ and ‘A Time.’” Apeiron XXII, 3 (September 1989), 208-09.