Authors/Thomas Aquinas/physics/L3/lect3

Lecture 3 Justification of the definition of motion

Latin	English
	Lecture 3 Justification of the definition of motion
lib. 3 l. 3 n. 1 Posita definitione motus et manifestatis singulis particulis definitionis, hic consequenter ostendit quod definitio sit bene assignata: et primo directe; secundo indirecte, ibi: quod autem bene dictum sit et cetera.	291. Having given the definition of motion and an explanation of each of the words in the definition, the Philosopher now shows it to be a good definition: Directly; Indirectly, at 293.
lib. 3 l. 3 n. 2 Circa primum utitur tali ratione. Omne quod est in potentia, quandoque contingit esse in actu; sed aedificabile est in potentia; ergo contingit aliquem actum esse aedificabilis inquantum est aedificabile. Hoc autem est vel domus vel aedificatio. Sed domus non est actus aedificabilis inquantum est aedificabile, quia aedificabile inquantum huiusmodi reducitur in actum cum aedificatur; cum autem iam domus est, non aedificatur. Relinquitur igitur quod aedificatio sit actus aedificabilis inquantum huiusmodi. Aedificatio autem est quidam motus: motus igitur est actus existentis in potentia inquantum huiusmodi. Et eadem ratio est de aliis motibus. Patet igitur quod motus sit talis actus qualis dictus est et quod tunc aliquid movetur, quando est in tali actu, et neque prius neque posterius: quia prius, cum est in potentia tantum, non incipit motus; neque etiam posterius, cum iam omnino desinat esse in potentia per hoc quod sit in actu perfecto.	292. In regard to the first [200 201 b5] he uses the following argument: Everything which is in potency may at some time be in act; but the “buildable” is in potency. Therefore, there may . at some time be an act of the “buildable” insofar as it is buildable. But this act is either the house itself or the building of it. But “house” is not the act of the “buildable” insofar as it is “buildable.” Since the “buildable” as such is being reduced into act when the building is taking place, but when the house now exists, it is no longer being built. Hence, building is an act of the buildable as such. Building, however, is a certain motion. Motion, therefore, is the act of a thing existing in potency as such. The same is true of other motions. It is clear, therefore, that motion is the type of act above-described, and that something is being moved only when it is in such an act, and neither before nor after—not before, since if it is only in potency the motion has not begun; nor after, since it has now completely ceased to be in potency, by virtue of being in perfect act.
lib. 3 l. 3 n. 3 Deinde cum dicit: quod autem bene dictum sit etc., ostendit indirecte definitionem esse bene assignatam, per hoc scilicet quod non contingit motum aliter definire. Et circa hoc tria facit: primo proponit quod intendit; secundo ponit definitiones aliorum de motu, et reprobat eas, ibi: manifestum autem intendentibus etc.; tertio assignat causam quare alii sic definierunt motum, ibi: causa autem in hoc ponere et cetera. Dicit ergo primo quod manifestum est motum esse bene definitum ex duobus: primo quidem quia definitiones quibus alii definierunt motum, sunt inconvenientes; secundo ex hoc quod non contingit eum aliter definire. Cuius ratio est, quia motus non collocari potest in aliquo alio genere quam in genere actus existentis in potentia.	293. Then [201 201 b16] he shows indirectly that it is a good definition by showing that motion cannot be defined in any other way. In regard to this he does three things: He proposes what he intends; He presents definitions given by others and rejects them, at 294. He explains why others defined motion as they did, at 295. He says therefore that two things show why the definition given of motion is a good one: First, because the definitions that others have given are unsuitable; Secondly, because it is impossible to define motion otherwise than as Aristotle has defined it, the reason being that motion cannot be placed in any other genus but that of “act of a thing existing in potency.”
lib. 3 l. 3 n. 4 Deinde cum dicit: manifestum autem intendentibus etc., excludit definitiones aliorum de motu. Et sciendum est quod tripliciter aliqui definierunt motum. Dixerunt enim motum esse alteritatem, propter hoc quod id quod movetur semper alio et alio modo se habet. Item dixerunt motum esse inaequalitatem, quia id quod movetur semper magis ac magis accedit ad terminum. Dixerunt etiam motum esse quod non est, idest non ens: quia id quod movetur, dum movetur, nondum habet id ad quod movetur; ut quod movetur ad albedinem, nondum est album. Has autem definitiones destruit philosophus tripliciter. Primo quidem ex parte subiecti motus. Si enim motus esset alteritas vel inaequalitas vel non ens, cuicumque ista inessent, necessario moveretur; quia cuicumque inest motus, illud movetur. Sed non est necessarium moveri neque ea quae sunt altera, ex hoc ipso quod altera sunt; neque inaequalia, neque ea quae non sunt. Relinquitur igitur quod alteritas et inaequalitas et non ens, non est motus. Secundo ostendit idem ex parte termini ad quem: quia motus et mutatio non est magis in alteritatem quam in similitudinem, neque magis in inaequalitatem quam in aequalitatem, neque magis in non esse quam in esse. Nam generatio est mutatio ad esse, et corruptio ad non esse. Non igitur motus magis est alteritas quam similitudo, vel inaequalitas quam aequalitas, vel non ens quam ens. Tertio ostendit idem ex parte termini a quo: quia sicut motus aliquis est ex alteritate et ex inaequalitate et ex non ente, ita est ex oppositis horum. Non igitur motus magis debet poni in his generibus, quam in oppositis.	294. Then [202 201 b19] he excludes the definitions of motion given by others. These followed a three-fold course in their definitions. For they said that motion is “otherness,” because the thing being moved constantly changes from one state to another. Similarly, they said motion is “unequalness,” because the thing being moved approaches its term always more and more. They also said that motion is “non-being,” because the thing being moved does not yet have that to which it is being moved as long as it is being moved—as that which is being moved toward whiteness is not yet white. These definitions the Philosopher destroys in three ways. He does so first by looking at the subject of motion. For if motion were “otherness” or “unequalness” or “non-being,” then whatever would possess any one of these three characteristics would of necessity be undergoing motion—in whatever this motion is, that thing is being moved. But things that are other are not necessarily being moved by the fact that they are “other,” nor by the fact that they are “unequal,” nor by the fact that they “do not exist.” It follows, therefore, that otherness and unequalness and non-being are not motion. Secondly, he shows the same thing by looking at the term to which the motion is tending for motion and change do not tend more to “otherness” than to “likeness,” or to “unequalness” more than to “equality,” or to “non-being” more than to “being.” For generation is a change to “being”, and corruption to “non-being.” Hence motion is not “otherness” any more than “a likeness,” “unequalness” any more than “equalness,” “non-being” any more than “being.” Thirdly, he shows the same thing by looking at the term from which the motion begins since just as some motions start from otherness and from unequalness and from non-being, so others start from their opposites. Hence there is no reason to place motion in the afore-mentioned genera any more than in their opposites.
lib. 3 l. 3 n. 5 Deinde cum dicit: causa autem in hoc ponere etc., assignat causam quare praedicto modo antiqui motum definierunt. Et circa hoc duo facit: primo assignat causam eius quod dictum est; secundo assignat causam cuiusdam quod supposuerat, ibi: videri autem indeterminatum et cetera. Dicit ergo primo quod ista est causa quare antiqui posuerunt motum in praedictis generibus (scilicet alteritatis, inaequalitatis et non entis), quia motus videtur esse quoddam indeterminatum, idest incompletum et imperfectum, quasi non habens determinatam naturam. Et quia indeterminatus est, propter hoc videtur esse ponendus in genere privativorum. Nam cum Pythagoras poneret duas ordinationes rerum, in quarum utraque ponebat quaedam decem principia; principia quae erant in secunda ordinatione, dicebantur ab ipso indeterminata, quia sunt privativa. Non enim determinantur per formam quae sit in genere substantiae, neque per formam qualitatis, neque per formam aliquam specialem in aliquo horum generum existentem, neque etiam per formam alicuius aliorum praedicamentorum. In una autem ordinatione ponebant Pythagorici haec decem; scilicet finitum, impar, unum, dexterum, masculum, quietem, rectum, lumen, bonum, triangulum aequilaterum: in alia autem, infinitum, par, multitudinem, sinistrum, feminam, motum, obliquum, tenebram, malum, altera parte longius.	295. Then [203 201 b24] he points out why some defined motion in the aforesaid ways. In regard to this he does two things: First he assigns the reason of what has already been stated. Secondly, he explains a supposition he had made, at 296. He says therefore that the reason why the older philosophers placed motion in the above-mentioned genera (namely, “otherness,” “unequalness” and “non-being”) is that motion seems to be something indeterminate, i.e., something incomplete and imperfect as though possessing no determinate nature. And because it is indeterminate, its proper place seemed to be in the genus of privation. For when Pythagoras laid down two ordinations of reality, in each of which he placed ten principles, the principles in the second group were said by him to be indeterminate because they were privative. They were not, indeed, determined by a form in the genus of substance, nor by the form of quality, or by any special form in either of these genera or by the form of any of the other predicaments. In one of these groups the Pythagoreans placed ten things: finite, unequal, one, right, male, rest, straight, light, good, equilateral triangle; in the other they placed: infinite, equal, many, left, female, motion, oblique, dark, evil and scalene triangle.
lib. 3 l. 3 n. 6 Deinde cum dicit: videri autem indeterminatum etc., assignat causam quare motus ponitur inter indeterminata. Et dicit quod huius causa est, quia neque potest poni sub potentia neque sub actu. Si enim poneretur sub potentia, quidquid esset in potentia, puta ad quantitatem, moveretur secundum quantitatem: et si contineretur sub actu, quidquid esset actu quantum, moveretur secundum quantitatem. Et quidem verum est quod motus est actus: sed est actus imperfectus, medius inter potentiam et actum. Et quod sit actus imperfectus ex hoc patet, quod illud cuius est actus, est ens in potentia, ut supra dictum est. Et ideo difficile est accipere quid sit motus. Videtur enim in primo aspectu quod vel sit simpliciter actus, vel simpliciter potentia, vel quod contineatur sub privatione, sicut antiqui posuerunt ipsum contineri sub non ente et sub inaequalitate. Sed nullum horum est possibile, ut supra ostensum est: unde relinquitur solus praedictus modus ad definiendum motum; ut scilicet motus sit actus talis qualem diximus, scilicet existentis in potentia. Talem autem actum considerare difficile est propter permixtionem actus et potentiae: tamen esse talem actum non est impossibile, sed contingens.	296. Then [204 201 b27] he gives the reason why motion is placed among the indeterminates. And he says that the reason for this is that motion cannot be placed either in potency or in act. For if it were placed under potency, whatever would be in potency, for example, to quantity, would be being moved according to quantity. If, on the other hand, it were included under act, then whatever things were actually quantified would be being moved according to quantity. Now it is indeed true that motion is act, yet it is imperfect act, a medium between potency and act. And that it is imperfect act is clear from the fact that that of which it is an act is a being in potency as stated above (l.2, no.285). And that is why it is difficult to grasp what motion is. For at first sight It seems to be either entirely act or entirely potency or else to be contained under privation as it seemed to the ancients who called it “non-being” or “unequalness.” But none of these is possible, as we have shown above (no.294). Hence it follows that there is just one way to define motion; namely, that it is the kind of act we have said, i.e., that of a thing existing in potency. It is difficult to dwell on such an act on account of the commingling of act and potency; yet that there should be such an act is not impossible, but contingent.