Authors/Thomas Aquinas/physics/L8/lect8

Lecture 8 What moves the heavy and light. Everything moved, moved by another

Latin	English
	Lecture 8 What moves the heavy and light. Everything moved, moved by another.
lib. 8 l. 8 n. 1 Postquam ostendit quod gravia et levia non movent seipsa, hic ostendit a quo moveantur. Et primo ostendit a quo moveantur; secundo concludit principale intentum, ibi: si igitur omnia quae moventur et cetera. Circa primum duo facit: primo ostendit quod naturaliter moventur ab aliquo; secundo inquirit a quo moveantur, ibi: quoniam autem quod potentia et cetera. Dicit ergo primo, quod etsi gravia et levia non moveant seipsa, tamen moventur ab aliquo. Et hoc potest manifestari, si distinguantur causae moventes. Sicut enim in his quae moventur, est accipere quaedam secundum naturam moveri, et quaedam extra naturam; ita et in moventibus quaedam movent extra naturam, ut vectis, idest baculus, qui non naturaliter motivus est corporis gravis, puta lapidis; quaedam vero movent secundum naturam, sicut quod est actu calidum naturaliter movet id quod secundum suam naturam est potentia calidum; et similiter est in aliis talibus. Et sicut quod est in actu naturaliter movet, ita id quod est in potentia naturaliter movetur, vel secundum qualitatem, vel secundum quantitatem, vel secundum ubi. Et quia in secundo dixerat quod illa moventur naturaliter, quorum principium motus in ipsis est per se, et non secundum accidens; ex quo posset videri quod id quod est in potentia tantum calidum, cum fit calidum, non movetur naturaliter, tanquam principio activo motus exterius existente: quasi ad hanc obiectionem excludendam subiungit: cum habeat principium huiusmodi in seipso, et non secundum accidens; quasi dicat quod ad hoc quod motus sit naturalis, sufficit quod huiusmodi principium, scilicet potentia, de qua fecerat mentionem, sit in eo quod movetur, per se et non per accidens, sicut scamnum est potentia combustibile, non inquantum est scamnum, sed inquantum est lignum. Unde hoc quod dixerat, non secundum accidens, exponens, subdit quod contingit idem subiectum esse et quantum et quale, sed unum eorum per accidens se habet ad aliud, et non per se: quod ergo est potentia quale, est etiam potentia quantum, sed per accidens. Quia igitur quod est in potentia, naturaliter movetur ab alio quod est in actu: nihil autem secundum idem est potentia et actu: sequitur quod neque ignis neque terra neque aliquid aliud moveatur a se, sed ab alio. Moventur quidem ignis et terra ab alio, sed per violentiam, cum motus eorum est extra naturalem ipsorum potentiam: sed naturaliter moventur, cum moventur in actus proprios, ad quos sunt in potentia secundum suam naturam.	1029. After showing that the heavy and the light do not move themselves, he shows by what they are moved. First he shows by what they are moved; Secondly, he concludes to his main intention, at 1036. About the first he does two things: First he shows that they are naturally moved by something; Secondly, he investigates by what they are moved, at 1030. He says therefore First (798 255 a18) that although the heavy and the light do not move themselves, they are nevertheless moved by something. And this can be made clear if we distinguish moving causes. For just as in things that are moved, we must take it that (1) some things are moved according to nature and some not, so also in movers, some move not according to nature, e.g., a stick, which is not naturally capable of moving a heavy body such as a stone; and that (2) some things move according to nature, as what is actually hot naturally moves what is according to its nature potentially hot, and similarly in other cases. And just as what is in act causes motion naturally, so what is in potency is naturally moved, with respect either to quantity or quality or where. And because in Book II he had said that those things are moved naturally whose principle of motion exists in them per se and not by virtue of some concomitant attribute, which might lead one to suppose that what is only potentially hot is, when it becomes hot, not moved naturally in that it is being moved by an external active principle of its motion, he now adds, as though to preclude this objection, “since it has a principle of this kind in itself and not accidentally,” as if to say that in order that a motion be natural, it is enough that a principle of this kind, i.e., the potency, about which he made mention, exist in that which is moved per se and not per accidens, as a bench is potentially combustible, not precisely as bench but as wood. Hence in explaining the expression “per accidens,” he adds that the same subject can be quantified and qualified, but one of these is related to the other per accidens; what is potentially of such and such a quality is also potentially quantified, but per accidens. Therefore, because what is in potency is naturally moved by something else in act, and nothing is in potency and in act with respect to the same, it follows that neither fire nor earth nor anything else is moved by itself but by another. Fire and water are moved by another, but by compulsion, when their motion is outside their natural potency; but they are moved naturally when they are moved to their proper acts, to which they are in potency according to their nature.
lib. 8 l. 8 n. 2 Deinde cum dicit: quoniam autem quod potentia etc., ostendit a quo moveantur: et quia quod est in potentia movetur ab eo quod est in actu, primo distinguit potentiam; secundo ex hoc ostendit a quo huiusmodi moveantur, ibi: potentia autem est leve et cetera. Circa primum tria facit: primo ostendit necessarium esse cognoscere quot modis aliquid dicitur esse in potentia; secundo manifestat, ibi: est autem potentia etc.; tertio solvit ex hoc quandam quaestionem, ibi: et tamen quaeritur et cetera. Dicit ergo primo, quod ideo non est manifestum a quo gravia et levia moventur suis motibus naturalibus, ut puta ignis sursum et terra deorsum, quia ens in potentia dicitur multipliciter.	1030. Then at (799 255 a30) he shows by what they are moved. And because what is in potency is moved by something in act, First he distinguishes potency; Secondly, from this he shows by what such things are moved, at 1035. About the first he does three things: First he shows that it is necessary to know the ways in which something is said to be in potency; Secondly, he explains this at 1031; Thirdly, with this he solves a question, at 1033. He says therefore that the reason why it is not evident by what heavy and light things are moved with respect to their natural motion (as fire upward and earth downward) is that the expression “being in potency” has many senses.
lib. 8 l. 8 n. 3 Deinde cum dicit: est autem potentia etc., distinguitur esse in potentia: et primo in intellectu; secundo in qualitate, ibi: similiter autem haec se habent etc.; tertio in motu locali, ibi: similiter autem se habet et cetera. Dicit ergo primo, quod aliter est in potentia ad scientiam ille qui addiscit et nondum habet habitum scientiae, et ille qui iam habet habitum scientiae sed non considerat utens habitu. Ex prima autem potentia in secundam reducitur aliquid, cum activum suo passivo coniungitur; et tunc passivum per praesentiam activi fit in tali actu, qui adhuc est in potentia; sicut addiscens per actionem docentis reducitur de potentia in actum, cui actui coniungitur altera potentia. Et sic existens in prima potentia, fit in alia potentia: quia iam habens scientiam, sed non considerans, quodammodo est in potentia ad actum scientiae, sed non eodem modo, sicut antequam addisceret. Ergo de prima potentia reducitur in actum cui coniungitur secunda potentia, per aliquod agens, scilicet per docentem. Sed quando sic se habet quod habet habitum scientiae, non oportet quod reducatur in secundum actum per aliquod agens, sed statim per seipsum operatur considerando, nisi sit aliquid prohibens, puta occupatio vel infirmitas aut voluntas. Vel si non impeditus non posset considerare, tunc non esset in habitu scientiae, sed in eius contrario, scilicet in ignorantia.	1031. Then at (800 255 a33) he distinguishes “being in potency”: First in the understanding; Secondly, in quality, at 1032; Thirdly, in local motion, at 1033. He says therefore first that one who is learning and does not yet have the habit of science is not in potency to science in the same way as one who already has the science but is not using it by considering. But something is reduced from the first potency to the second, when the active principle is united with the patient; and then the patient through the presence of the active principle comes to be with respect to such an act, but after that the patient is yet in potency: for example, a learner is through the action of the teacher reduced from potency to act, but when he is in this state of act, there is yet another potency present. Consequently, the thing existing in first potency comes to be in another state of potency; because one having science, and not considering, is in a sense in potency to an act of science, but not in the same way as he was before he learned. Therefore, from first potency he is reduced to an act to which is united a second potency, by some agent, namely, the teacher. But when he is in the state of possessing the habit of science, it is not necessary that he be reduced to second act by some agent; rather he operates immediately by himself, just by considering, i.e., unless he is prevented by other occupations or by sickness or by his will. On the other hand, if he were not impeded and still could not consider, then he would not be in the habit of science but in its contrary, namely, ignorance.
lib. 8 l. 8 n. 4 Deinde cum dicit: similiter autem haec etc., manifestat idem in qualitatibus. Et dicit quod sicut dictum est de potentia ad sciendum in anima, ita est etiam in corporibus naturalibus. Corpus enim cum est actu frigidum, est potentia calidum, sicut ignorans est potentia sciens: sed cum fuerit productum per transmutationem ut habeat formam ignis, tunc iam est ignis in actu, habens virtutem operandi; et operatur statim comburendo, nisi aliquid prohibeat in contrarium agendo, vel qualitercumque aliter impediat, puta subtrahendo combustibile; sicut dictum est quod postquam aliquis addiscendo factus est sciens, statim considerat, nisi aliquid impediat.	1032. Then at (801 255 b5) he manifests the same thing in qualities. And he says that what was said with respect to the potency of anything in the mind applies also to natural bodies. For when a body is actually cold, it is potentially hot, just as an ignorant person is potentially a knower. But when this body has been so modified that it has the form of fire, then it is now actually fire and has the power to burn; and it acts at once and burns, unless it is prevented by something acting to the contrary or somehow preventing its acting, as by removing the combustible material. This is similar to what was said above, that when someone after learning becomes a knower, he at once considers, unless prevented by something.
lib. 8 l. 8 n. 5 Deinde cum dicit: similiter autem se habet et circa grave etc.; manifestat idem in motu locali gravium et levium. Et dicit quod similiter leve fit ex gravi, sicut calidum ex frigido; ut puta cum aer, qui est levis, fit ex aqua, quae est gravis. Haec ergo, scilicet aqua, primo est in potentia levis, et postmodum fit levis in actu; et tunc statim habet operationem suam, nisi aliquid prohibeat. Sed iam levis existens comparatur ad locum sicut potentia ad actum (actus enim levis, inquantum huiusmodi, est esse in aliquo loco determinato, scilicet sursum): sed prohibetur ne sit sursum, per hoc quod est in contrario loco, scilicet deorsum, quia non potest esse simul in duobus locis: unde illud quod detinet leve deorsum, prohibet ipsum esse sursum. Et sicut dictum est in motu locali, ita etiam dicendum est de motu secundum quantitatem vel qualitatem.	1033. Then at (802 255 b8) he manifests the same thing in the local motion of the heavy and the light. And he says that a light thing comes to be from a heavy, as a hot thing comes to be from the cold, as, for example, when air which is light comes to be from water which is heavy. Therefore, this water is first potentially light and later becomes actually light, and then it has its own activity at once, unless something prevents. But now being light, it is related to a place as potency to act—for the act of the light as light is to be in some definite place, namely, above; but it is prevented from being up by the fact of being in a contrary place, namely, down, because it cannot be in two places at the same time. Hence, that which keeps a light thing down prevents it from being up. And what has been said of local motion is true also of motion with respect to quantity or quality.
lib. 8 l. 8 n. 6 Deinde cum dicit: et tamen quaeritur etc., solvit quandam quaestionem secundum praemissa. Licet enim actus levis sit esse sursum, tamen a quibusdam quaeritur quare gravia et levia moventur in propria loca. Sed causa huius est, quia habent naturalem aptitudinem ad talia loca. Hoc enim est esse leve, habere aptitudinem ad hoc quod sit sursum: et haec est etiam ratio gravis, habere aptitudinem ad hoc quod sit deorsum. Unde nihil est aliud quaerere quare grave movetur deorsum, quam quaerere quare est grave. Et sic illud idem quod facit ipsum grave, facit ipsum moveri deorsum.	1034. Then at (803 255 b13) he uses the foregoing to answer a question. For although the act of the light is to be above, yet some ask why the heavy and the light are moved to their appropriate places. But the cause of this is that they have a natural aptitude for such places. For to be light is to have an aptitude for being above, and the nature of the heavy is to have an aptitude to be down. Hence, to ask why a heavy thing is moved downward is exactly the same as to ask why it is heavy. Accordingly, the very same thing that makes it heavy makes it be moved downward.
lib. 8 l. 8 n. 7 Deinde cum dicit: potentia autem est leve etc., ex praemissis ostendit quid moveat gravia et levia. Et dicit quod cum id quod est in potentia, moveatur ab eo quod est in actu, sicut dictum est, considerandum est quod multipliciter dicitur aliquid esse in potentia leve vel grave. Uno enim modo, cum adhuc est aqua, est in potentia ad leve: alio autem modo, cum iam ex aqua factus est aer, est tamen adhuc in potentia ad actum levis, quod est esse sursum, sicut habens habitum scientiae et non considerans, adhuc dicitur esse in potentia; contingit enim quod id quod est leve, impediatur ne sit sursum. Si ergo auferatur illud impedimentum, statim agit ad hoc quod sit sursum ascendendo; sicut etiam dictum est in qualitate, quod quando est quale in actu, statim tendit in suam actionem; sicut ille qui est sciens, statim considerat, nisi aliquid prohibeat. Et similiter in motu quantitatis: quia ex quo facta est additio quanti ad quantum, statim sequitur extensio in corpore augmentabili, nisi aliquid prohibeat. Sic ergo patet quod illud quod movet, idest removet hoc quod est prohibens et sustinens, idest detinens, quodammodo movet et quodammodo non movet: puta si columna sustineat aliquod grave, et sic impediat ipsum descendere, ille qui divellit columnam, quodammodo dicitur movere grave columnae superpositum; et similiter ille qui removet lapidem qui impedit aquam effluere a vase, dicitur quodammodo movere aquam. Dicitur enim movere per accidens, et non per se: sicut si sphaera, idest pila, repercutiatur a pariete, per accidens quidem mota est a pariete, non autem per se; sed a primo proiiciente per se mota est. Paries enim non dedit ei aliquem impetum ad motum, sed proiiciens: per accidens autem fuit, quod dum a pariete impediretur ne secundum impetum ferretur, eodem impetu manente, in contrarium motum resilivit. Et similiter ille qui divellit columnam, non dat gravi superposito impetum vel inclinationem ad hoc quod sit deorsum: hoc enim habuit a primo generante, quod dedit ei formam quam sequitur talis inclinatio. Sic igitur generans est per se movens gravia et levia, removens autem prohibens, per accidens. Concludit igitur manifestum esse ex dictis, quod nihil horum, scilicet gravium et levium, movet seipsum: sed tamen motus eorum est naturalis, quia habent principium motus in seipsis; non quidem principium motivum aut activum, sed principium passivum, quod est potentia ad talem actum. Ex quo patet contra intentionem philosophi esse, quod in materia sit principium activum, quod quidam dicunt esse necessarium ad hoc quod sit motus naturalis: sufficit enim ad hoc passivum principium, quod est potentia naturalis ad actum.	1035. Then at (804 255 b17) he uses the foregoing to show what moves the heavy and the light. And he says that since what is in potency is moved by what is in act (as has been said), it must be considered that something is said in many senses to be potentially light or heavy. For in one way, when something is yet water, it is in potency to lightness; in another way, when from the water air has now been made, it is still in potency to the act of what is light, which is to be above in the same way that one having the habit of science and not considering is said still to be in potency—for what is light can possibly be prevented from being up. If, therefore, that obstacle be removed, it immediately acts for the purpose of being up by ascending, as it was said with respect to quality that when a thing is actually of such and such a quality, it immediately tends to its act, as a knower immediately considers, unless he be prevented. And the same is true with respect to the motion to quantity, for from the fact that an addition of quantity has been made to a quantitative thing, extension immediately follows in an increasable body, unless something prevents. Accordingly, it is clear that what moves, i.e., what removes the obstacle preventing and sustaining does in some sense cause motion and in other senses does not; for example, if a pillar supports something heavy and thus keeps it from descending, the one who casts down the pillar is said somehow to move the heavy object that was supported by the pillar. In like manner, one who removes a stopper that was preventing water from flowing out of a container is said in some sense to move the water; for he is said to move per accidens and not per se. Also when a ball rebounds from a wall, it is moved per accidens by the wall but per se by the one who first threw it. For it was not the wall but the thrower that gave it the impetus for motion; but it was per accidens that, being prevented by the wall from continuing according to its impetus, it rebounded into a contrary motion, the original impetus remaining. In like manner, the one who casts down the pillar did not give the heavy object resting upon it the impetus or inclination to be downward, for it had that from the first generator, which gave it the form upon which that inclination follows. Consequently, the generator is the per se mover of the light and the heavy, whereas the remover of obstacles is a per accidens mover. He concludes, therefore, that it is clear from the foregoing that none of these, i.e., of the heavy and the light, moves itself; yet their motion is natural, because they have in themselves the principle of their motion, not indeed a moving or active principle but a passive one, which is a potency to such-and-such an act. From this it is evidently contrary to the intention of the Philosopher that in matter there be an active principle, which some declare is necessary for a natural motion; for a passive principle is sufficient, since it is a natural potency for act.
lib. 8 l. 8 n. 8 Deinde cum dicit: si igitur omnia quae moventur etc., concludit conclusionem principaliter intentam in toto capitulo. Et dicit quod si hoc verum est, quod omnia quae per se moventur, aut moventur secundum naturam, aut extra naturam et per violentiam; et de illis quae moventur per violentiam, manifestum est quod omnia moventur non solum a quodam movente, sed etiam a movente alio extrinseco; et iterum inter ea quae moventur secundum naturam, quaedam moventur a seipsis, in quibus manifestum est quod moventur ab aliquo, non quidem extrinseco, sed intrinseco; quaedam etiam sunt quae moventur secundum naturam, non tamen a seipsis, sicut gravia et levia, et haec etiam ab aliquo moventur, ut ostensum est (quia aut moventur per se a generante, quod facit ea esse gravia et levia; aut moventur per accidens ab eo quod solvit, idest removet, ea quae impediunt vel removent naturalem motum): sic ergo patet quod omnia quae moventur, moventur ab aliquo vel intrinseco motore vel extrinseco, quod dicit ab alio moveri.	1036. Then at (805 255 b31) he concludes to the conclusion chiefly intended in the whole chapter. And he says that if it is true that all things which are per se moved are moved either according to nature, or outside their nature and by compulsion, and if of those which are moved by compulsion it is true that all are moved not only by a mover but even by an external mover that is other; and, again, if among things that are moved according to nature, some are moved by themselves—in which things it is clear that they are moved by something not extrinsic but intrinsic—while others, such as heavy and light things are moved according to nature not by themselves but by some mover) as has been explained—for they are moved either per se by the generator which makes them be heavy and light, or they are moved per accidens by whatever removes what impedes or removes their natural motion—it is accordingly clear that all things which are moved are moved by something, i.e., either by an intrinsic or an extrinsic mover; which is to be moved by something other.