Aristotle’s Reflections on Time

Aristotle notes in the Physics that ‘time is mostly supposed to be motion and a kind of change’ (dokei malista kinêsis einai kai metabolê tis ho chronos, 218b9-10). He says ‘that it is not movement’ (hoti men toinun ouk estin kinêsis, 218b18), ‘but that it does not exist without change’ (alla mên oud aneu ge metabolês, 218b21). The switch from ‘movement’ (kinêsis) to ‘change’ (metabolê) is intentional; Aristotle he could have equally well said that ‘time is not change, yet does not exist without movement’, for he remarks: ‘let it make no difference at present whether we say movement or change’ (mêden de diapheretȏ legein hêmin en tȏi paronti kinêsin ê metabolên, 218b19-20). But if we pay attention to his use of these two terms, we shall find that they play different role in his reflections on time.

The notion of ‘change’ is prominent when he speaks of our perception of time: ‘when we don’t change the state of our own minds in any respect (hotan gar mêden autoi metaballȏmen tên dianoian), or we have not noticed our changing it (ê lathȏmen metaballontes), it does not seem to us that time occurred (ou dokei hêmin gegonenai chronos, 218b21-23). The concept of ‘movement’ comes to prominence when the question is of knowing time: ‘but we gain knowledge of time only (alla mên kai ton chronon ge gnȏrizomen) when we have demarcated movement (hotan horisȏmen tên kinêsin) by the before and after (tȏi proteron kai husteron horizontesˑ) … for time is just this (touto gar estin ho chronos): number of motion in respect of the before and after (arithmos kinêseȏs kata to proteron kai husteron)’ (219a14-b2). ‘We measure movement by time (tên kinêsin tȏi chronȏi metroumen) and by movement time (kai têi kinêsei ton chronon), because they demarcate and define each other (dia to horizesthai hup’ allêlȏn). Time demarcates movement (ho men gar chronos horizei tên kinêsin) since it is its number (arithmos ȏn autês), and movement time’ (hê de kinêsis ton chronon) (220b14-18) … because by motion demarcated by time (hoti hupo tês hȏrismenês kinêseȏs chronȏi) the quantity both of motion and of time is measured (metreitai tês te kinêseȏs to poson kai tou chronou). The primary measure of time (to prȏton metron) is the circular motion (hê kuklophoria), for it is regular (homalês) and its number is best known (ho arithmos ho tautês gnȏrimȏtatos, 223b16-20). Ross notes that the circular motion owes its primacy to the fact that a single revolution is a natural unit of a circular motion; units of other motions must be taken arbitrarily. It is best known, for the heavenly bodies are known to all. (I have not marked Ross’ words by quotation marks, for I do not have his edition of the Physics. I have jotted his remark on the margin of my copy of the book when I read Ross’ edition in Bodleian Library at Oxford; to my marginal I added ‘that the circular motion owes its primacy to the fact ‘and ‘It is best known, for’.)

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The most remarkable aspect of Aristotle’s reflections on time in the Physics is the absence of the present: time is in his view composed (sunkeitai) of the part that has been (to men oun autou gegone) and is not (kai ouk estin), and of the part that is going to be (to de mellei) and is not yet (kai oupȏ estin, 217b33-218a2). The ‘now’ (to nun) plays an important role in his deliberations about time, ‘but it is not a part of time’ (to de nun ou meros, 218a6); it demarcates time as the body that moves demarcates movement: “The ‘now’ follows the body carried along (tȏi de pheromenȏi akoluthei to nun), as time follows motion (hȏsper ho chronos têi kinêsei), for we gain knowledge of the ‘before and after’ in motion by means of the body carried along (tȏi gar pheromenȏi gnȏrizomen to proteron kai husteron en kinêsei), and the ‘now’ is (to nun estin) in so far as the ‘before and after’ is countable (hêi arithmêton to proteron kai husteron, 219b22-25) … the ‘now’ is like a body that is carried along (to nun de hȏs to pheromenon), it is like a unit in number (hoion monas arithmou, 220a4). For time is the number of motion (chronos men gar ho tês phoras arithmos); it is made continuous by virtue of the ‘now’ (kai sunechês ho chronos tȏi nun), and is divided in accordance with the ‘now’ (kai diêirêtai kata to nun, 220a3-5). True to his conceptual derivation of time as number from motion in place/space, Aristotle  views the ‘now’ in terms of a point in a line, ‘for the point too connects the length and determines it (kai gar hê stigmê kai sunechei to mêkos kai horizei); it is the beginning of one part and the end of another (esti gar tou men archê tou de teleutê, 220a10-11).’

In Aristotle’s view, ‘if there were no time (eite chronos mê eiê), there would not be the ‘now’ (to nun ouk an eiê), and if the ‘now’ were non-existent (eite to nun mê eiê), there would not be time (chronos ouk an eiê, 219b35-220a1)’, but the ‘now’ he thus contemplates has nothing to do with the present as an aspect of time.

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The present nevertheless comes into its own in the Rhetoric, where Aristotle maintains that ‘all that is pleasurable (panta ta hêdea) must be (anankê) either present in being actually perceived (ê en tȏi aisthanesthai einai paronta) or in being remembered as past (ê en tȏi memnêsthai gegenêmena) or in being hoped for as coming in future (ê en tȏi elpizein mellonta). For people perceive the present pleasures (aisthanontai men gar ta paronta), remember the past ones (memnêntai de ta gegenêmena), and hope for the pleasures to come (elpizousi de ta mellonta, 1370a32-35).’ The present is here reflected by Aristotle as the primary field of experience, the past and the future come to the view in so far as they participate in the present as memories or expectations. If the present is good, then even the memory of the past difficulties is pleasurable (1370b1-10).

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In the On the Soul Aristotle appears to be viewing time and the ‘now’ very differently from the way he viewed them in the Physics. He reflects on these two notions in his discussion of sensory perception, and one must pay due attention to this  discussion to get to the point.

Aristotle says that ‘each sensory perception (hekastê aisthêsis) is of the underlying sensible thing (tou hupokeimenou aisthêtou estin) and belongs to the sensory organ (huparchousa en tȏi aisthêtêriȏi) that specifically senses that kind of things (hêi aisthêtêrion) and discriminates the differences in the underlying perceptible (kai krinei tas tou hupokeimenou aisthêtou diaphoras), as sight distinguishes white and black (hoion leukon kai melan opsis), but taste sweet and bitter’ (gluku de kai pikron geusis, 426b8-10). – I have allowed myself the liberty of coining the term ‘the perceptible’ to express Aristotle’s aisthêton, i. e. ‘that which is or can be perceived by senses’. – He then notes that we view white and sweet as different, and in general discriminate each perceptible from any other perceptible. These differences must be perceived by a faculty of sense (aisthêsei), for they are perceptibles (aisthêta gar estin), which in his view makes it clear that there must be the ultimate sense organ which is not made of flesh (hêi kai dêlon hoti hê sarx ouk esti to eschaton aisthêtêrion), for if it were, it would have to discriminate the two by touching them (anankê gar an ên haptomenon auto krinein to krinon). Furthermore, the sweet cannot be perceived as different from the white by separate agencies (oute dê kechȏrismenois endechetai krinein hoti heteron to gluku tou leukou), but both must be made clear as different from each other by something that is one (alla dei heni tini amphȏ dêla einai, 426b12-19). For if the two were to be perceived as different by two different sensory agencies, ‘it would be the same as if their mutual difference were to be made clear by my perceiving the one and you the other (houtȏ men gar k’an ei tou men egȏ tou de su aisthoio, dêlon an eiê, hoti hetera allêlȏn); but it is the one that must say that they are different (dei de to hen legein hoti heteron), for the sweet is different from the white (heteron gar to gluku tou leukou); it is therefore the same one that says this (legei ara to auto); so that as it says this (hȏste hȏs legei), so it thinks and perceives it (houtȏ kai noei kai aisthanetai, 426b19-22).

Aristotle concludes: ‘it is thus clear that by separate entities separate things cannot be discerned (hoti men oun ouch hoion te kechȏrismenois krinein ta kechȏrismena, dêlon); that they can’t be discerned in separate time either (hoti d’ oud’ en kechȏrismenȏi chronȏi) becomes clear from the following (enteouthen): For just as the one and the same says (hȏsper gar to auto legei) that the good and the bad is different (hoti heteron to agathon kai to kakon), so also when it says that the one is different and the other is different [must be one and undivided] (houtȏ kai hote thateron legei hoti heteron kai thateron), the when is not accidental (ou kata sumbebêkos to hote) {as when I now say that it is different (hoion nun legȏ hoti heteron), but not that it is different now (ou mentoi hoti nun heteron)};  but the undivided one says thus (all’ houtȏ legei) both now and that now (kai nun kai hoti nun), together therefore (hama ara); so that it must be undivided and in undivided time (hȏste achȏriston kai en achȏristȏi chronȏi, 426b22-29).’

Aristotle used the sweet and the white as examples, but he could have used the ‘before and after’, which he views as constitutive of our perception of time in the Physics, for from the point of view of the On the Soul it must be the one and the same undivided one that perceives the past as different from the future in undivided time. The difference between undivided time in the On the Soul and time defined as number of motion in the Physics cannot be explained by the difference of the subject matter that these treatises discuss, for in his deliberations about time in the Physics Aristotle asks ‘how the time is related to the soul’ (pȏs pote echei ho chronos pros tên psuchên, 223a16-17), but because of his being confined to his definition of time as an attribute of motion (kinêseȏs ti pathos ê hexis) as its number (arithmos ge ȏn, 223a18-19), the only thing in which he is there interested is the question, ‘which someone might ask (aporêseien an tis), whether if soul did not exist (poteron de mê ousês psuchês) time would exist or not (eiê an ho chronos ê ou, 223a21-22) … for if nothing but soul and intellect in soul can count (ei de mêden allo pephuken arithmein ê psuchê kai psuchês nous), there can be no time without soul (adunaton einai chronon psuchês mê ousês, 223a25-26). Aristotle solves the problem by saying that ‘time would be what it is (touto ho pote on estin ho chronos), if movement can exist without soul (ei endechetai kinêsin einai aneu psuchês); and the ‘before and after’ are in movement (to de proteron kai husteron en kinêsei estin), and time is these in so far as they are countable (chronos de taut’ estin hêi arithmêta estin, 223a27-29).