Authors/Thomas Aquinas/physics/L8/lect9

Lecture 9 No process to infinity in movers. Not every mover need be moved

Latin	English
	Lecture 9 No process to infinity in movers. Not every mover need be moved.
lib. 8 l. 9 n. 1 Postquam philosophus ostendit quod omne quod movetur ab alio movetur, hic incipit ostendere quod necesse est devenire ad aliquod primum movens immobile. Et dividitur in partes duas: in prima ostendit quod necesse est devenire ad aliquod primum, quod vel sit immobile, vel moveat seipsum; in secunda ostendit quod etiam si deveniatur ad aliquod primum quod moveat seipsum, necesse est tamen ulterius devenire ad aliquod primum movens immobile, ibi: necesse igitur omne quod movetur et cetera. Circa primum duo facit: primo ostendit quod non est possibile quod in infinitum aliquid ab alio moveatur; in secunda quod non est necessarium quod omne movens moveatur, ibi: ad dicta autem et cetera. Circa primum duo facit: primo ostendit propositum ascendendo in ordine mobilium et moventium; secundo descendendo, ibi: amplius autem et sic ipsam et cetera. Circa primum duo facit: primo praemittit quaedam necessaria ad propositi ostensionem; secundo inducit rationem ad propositum ostendendum, ibi: si ergo necesse et cetera.	1037. After showing that whatever is moved is moved by another, the Philosopher now begins to show that it is necessary to reach a first immobile mover. And his treatment is divided into two parts. In the first he shows that it is necessary to reach a first that is either immobile or moves itself; In the second he shows that even if a first that moves itself is reached, it is further necessary to reach a first mover that is immobile, (L.10). About the first he does two things: First he shows that it is not possible that things be moved by another ad infinitum; Secondly, he shows that not every mover need be moved, at 1042. About the first he does two things: First he explains the proposition by ascending in the order of mobiles and movers; Secondly, by descending, at 1041. About the first he does two things: First he premises things needed for manifesting his proposition; Secondly, he gives an argument that shows the proposition, 1040.
lib. 8 l. 9 n. 2 Praemittit autem duo: quorum primum est divisio moventis. Cum enim dictum sit quod omne motum ab aliquo movetur, contingit aliquid esse movens dupliciter. Uno modo quando non movet propter seipsum, idest propria virtute, sed quia est motum ab aliquo alio movente; et hoc est secundum movens. Alio modo aliquid movet propter seipsum, idest propria virtute, non quia est motum ab alio. Contingit autem quod tale movens moveat dupliciter. Uno modo ita quod primum movens moveat proximum post ultimum, idest id quod est sibi proximum post secundum movens; et hoc contingit quando primum movens movet mobile per unum tantum medium. Alio vero modo movens movet mobile per plura media, ut patet cum baculus movet lapidem et movetur a manu, quae movetur ab homine, qui non movet eo quod ab aliquo alio moveatur: sic ergo homo est primum movens propter seipsum, et movet lapidem per plura media; si autem moveret lapidem manu, moveret per unum medium tantum.	1038. Now he premises two things, of which the First (806 256 a4) is a division of movers. For since it has been said that whatever is moved is moved by something, a thing might be a mover in two senses. In one sense, when it moves not on its own account, i.e., not by its own power, but because it has been moved by some other mover. This is a second mover. In another sense, something moves on its own account, i.e., by its own power and not because it has been moved by another. Now, such a mover can cause motion in two ways: First, in such a way that the first mover moves the one next to the last, i.e., the one which is nearest to it after the second mover; this happens when the first mover moves a mobile through just one intermediate. Secondly, in such a way that the mover moves a mobile through a number of intermediates, as when a stick moves a stone and the stick is moved by a hand, which is moved by a man who does not move as being moved by something else. In this way the man is a first mover on his own account and he moves the stone through a number of intermediates; however, if he moved the stone with his hand, he would be moving the tone through one intermediate only.
lib. 8 l. 9 n. 3 Secundo ibi: utraque igitur movere dicimus etc., ponit comparationem primi moventis et secundi. Cum enim tam primum movens quam ultimum movere dicamus, dicimus quod magis movet primum movens quam ultimum. Et hoc patet per duas rationes. Quarum prima est, quod primum movens movet secundum movens, sed non e converso. Secunda ratio est, quia secundum movens non potest movere sine primo, sed primum movens potest movere sine secundo; sicut baculus non potest movere lapidem nisi moveatur ab homine, sed homo potest movere etiam sine baculo.	1039. Secondly, at (807 256 a8) he compares the first mover with the second. For since both the first mover and the ultimate are said to cause motion, we say that the first mover is more a mover than the ultimate mover. This is clear for two reasons: first, because the first mover moves the second mover but not vice versa; secondly, because the second mover cannot cause motion independently of the first, but the first can cause it independently of the second. For example, the stick cannot move the stone unless it is moved by the man, but the man can move the stone without using the stick.
lib. 8 l. 9 n. 4 Deinde cum dicit: si ergo necesse etc., ostendit propositum secundum praemissa. Ostensum est enim quod omne quod movetur, ab aliquo movetur. Illud autem a quo movetur, aut movetur aut non movetur; et si movetur, aut ab alio movetur aut non. Haec autem duo, scilicet quod movetur ab alio, et quod movetur non ab alio, sic se habent quod posito uno ponitur aliud, et non e converso. Quia si sit aliquid quod movetur ab alio, necesse est devenire ad aliquod primum quod non movetur ab alio; sed si ponatur aliquod primum huiusmodi, scilicet quod non moveatur ab alio, non est necessarium ulterius ponere alterum, scilicet quod movetur ab alio. Et hoc quidem per se manifestum est: sed primum poterat esse dubium, scilicet quod si invenitur aliquid quod movetur ab alio, quod inveniatur aliquod primum quod non movetur ab alio; et ideo consequenter hoc probat sic. Quia si aliquid movetur ab alio, et iterum illud ab alio, et nunquam est devenire ad aliquid quod non moveatur ab alio, sequitur quod sit procedere in infinitum in moventibus et motis. Et hoc quidem esse impossibile, supra probatum est in septimo: sed hic probat certiori via, quia in infinitis non est aliquid primum. Si ergo moventia et mota procedant in infinitum, non erit aliquid primum movens. Iam autem dictum est, quod si primum movens non movet, nec ultimum movet: non ergo erit aliquod movens: quod est manifeste falsum. Non est ergo procedere in infinitum in hoc quod aliquid moveatur ab alio. Si ergo detur quod omne quod movetur ab aliquo movetur, ut ostensum est; et iterum supponatur quod primum movens movetur: cum probatum sit quod non moveatur ab alio, necesse est quod moveatur a seipso. Est autem in hac ratione attendendum, quod primum movens moveri non est hic probatum; supponit autem hoc secundum communem opinionem Platonicorum. Quantum autem ad virtutem rationis, non magis concluditur quod primum movens moveat seipsum, quam quod sit immobile: unde in sequentibus hanc eandem conclusionem sub disiunctione inducit, ut infra patebit.	1040. Then at (808 256 a13) he proves his proposition in the light of the foregoing. For it has been shown that whatever is being moved is being moved by another. But that by which it is moved is itself either moved or not moved; and if it is moved, it is either moved by another or not. Now these two, namely, being moved by another or not being moved by another, are such that if one is posited the other must be and not vice versa: that is, if there is something which is moved by another, it is necessary to come to a first that is not moved by another; but if such a first is posited, namely, a first that is not moved by another, it is not necessary further to posit another, namely, one that is moved by another. This, indeed, is self-evident, but there could be some doubt about the first one, namely, that if there be found something moved by another, there be found a first that is not moved by another. For this reason, he proves this in the following manner. If something is moved by another and this in turn by another, and if something not moved by another is never reached, it follows that there is a process to infinity in movers and moved things. But this is impossible, as was proved in Book VII. However, he here proves it in a more certain way, from the fact that there is no first in an infinite series. Therefore, if movers and moved things go on ad infinitum, there will be no first mover. But it has already been said that if the first mover does not act, the last mover does not act and, consequently, there will be no mover, which is evidently false. Therefore, the process of something being moved by another cannot go on ad infinitum. If, therefore, it be conceded that whatever is being moved is being moved by another, as has been proved, and again, if it be supposed that the first mover is itself being moved but not by something else, it is necessarily being moved by itself. It should be noted that this argument is not proving that the first mover is being moved, but he is supposing this according to the common opinion of the Platonists. As to the force of the argument, it does not conclude more that the first mover moves itself than that it is immobile. Hence he later presents this same conclusion under a disjunction, as will be clear below.
lib. 8 l. 9 n. 5 Deinde cum dicit: amplius autem et sic ipsam etc., probat idem descendendo. Et est eadem ratio cum praemissa quantum ad virtutem inferendi, differens autem secundum ordinem processus: iterat autem eam ad maiorem manifestationem. Dicit ergo quod praedictam rationem contingit alio modo prosequi. Et praemittit propositiones habentes eandem rationem veritatis cum supra praemissis, sed alio ordine. Supra enim praemisit quod omne quod movetur ab alio movetur, et quod illud a quo movetur, movet vel propter seipsum, vel propter aliud prius movens; quod erat procedere ascendendo. Hic autem e converso descendendo procedit, dicens quod omne movens movet aliquid et movet aliquo, vel seipso vel alio inferiori movente; sicut homo movet lapidem vel ipse per seipsum vel per baculum, et ventus proiicit ad terram aliqua aut suo impulsu aut per lapidem quem movit. Iterum supra praemiserat quod ultimum movens non movet sine primo, sed e converso: loco cuius hic dicit, quod id quo aliquid movet sicut instrumento, impossibile est quod aliquid moveat sine principali movente quod movebat ipsum, sicut baculus sine manu; sed si aliquid movet per seipsum sicut principale movens, non est necesse esse aliud instrumentum quo moveat. Et hoc magis manifestum est in instrumentis quam in mobilibus ordinatis, licet habeat eandem veritatem; quia non quilibet consideraret secundum movens esse instrumentum primi. Sicut etiam supra dixerat deducendo, quod si sit aliquid quod movetur ab alio, necesse est esse aliquid quod non movetur, sed non e converso: ita hic dicit descendendo, quod si inveniatur quod illud quo movens movet, sit alterum, sicut instrumentum, necesse est esse aliquid quod movebit non aliquo instrumento, sed per seipsum, aut procedetur in infinitum in instrumentis; quod est idem ac si procederetur in infinitum in moventibus, quod est impossibile, ut supra ostensum est. Si ergo est aliquid movens id quod movetur, necesse est stare et non in infinitum ire. Quia si baculus movet eo quod movetur a manu, sequitur quod manus moveat baculum; si autem et manum aliquid aliud movet, etiam sequitur e converso quod aliquod movens moveat manum; et ita oportet quod sicut proceditur in instrumentis motis, ita procedatur in moventibus quae movent instrumenta. Non est autem procedere in infinitum in moventibus, ut supra ostensum est; ergo neque in instrumentis. Cum ergo semper alterum quod movetur, moveatur alio movente, et non sit procedere in infinitum; necesse est esse aliquod primum movens quod moveat per seipsum, et non per aliquod instrumentum. Si ergo detur quod hoc primum quod movet per seipsum, movetur quidem, sed non est aliquid aliud movens ipsum (quia sic et ipsum esset instrumentum); sequitur ex necessitate quod ipsum seipsum moveat: supposito, secundum Platonicos, quod omne movens movetur. Unde et secundum istam rationem illud quod movetur, aut statim movebitur a movente quod movet seipsum, aut aliquando erit devenire in aliquod tale movens quod seipsum moveat.	1041. Then at (809 256 a21) he proves his proposition by descending. And it is the same argument as the preceding so far as its illative value is concerned, but differs with respect to the order of the process; he repeats it, however, for the sake of greater clarity. He says therefore that the previous argument might be presented in another way. And he premises propositions that have the same truth value as the previous ones, but in a different order. For above he had premised that whatever is being moved is being moved by another and that that by which it is moved acts either on its own account or on account of something else previously moving it; and this was an ascending process. But now he uses a descending process, saying that every mover moves something and moves by means of something, i.e., either by itself or by means of some lesser mover, as a man moves a stone either by himself or by means of a stick and the wind casts something to the earth either by its own impulse or by means of a stone which it moves. Again, he had premised above that the last mover does not cause motion independently of the first mover, but vice versa. In place of that he here says that what a mover uses as an instrument in causing motion cannot itself cause motion without a principal mover moving it, as a stick cannot cause motion independently of the hand; but if something moves by itself as a principal mover, the addition of an instrument is not required. And this is more evident in instruments than in an ordered array of mobiles, although the same truth is present in both cases, because not every one would consider the second mover an instrument of the first. But as he deduced above that, if there is something that is being moved by another, there must be something that is not being moved, but not vice versa, so here in a descending process he says that if that by which the mover causes motion is another thing, as an instrument, there has to be something which causes motion not by an instrument but by itself. Otherwise, there is an infinite process with respect to instruments, which is the same as proceeding to infinity with respect to movers, and that is impossible, as has been proved above. If, therefore, there exists a mover of that which is being moved, a halt must be made and the process cannot go to infinity. For if the stick causes motion because it is moved by the hand, it follows that the hand moves the stick; if, however, something else is moving the hand, it also follows conversely that a mover is moving the hand. Consequently, the same process that was valid with respect to moved instruments is valid for movers of instruments. But with respect to movers, as was shown, an infinite process must be avoided; therefore, it must be avoided with respect to instruments. Therefore, since it is always so that a thing being moved is moved by another which moves, and an infinite process must be avoided, it is necessary that there be a first mover that moves by itself and not through an instrument. If, therefore, it be granted that this first which moves itself is indeed moved but there is no other moving it (because then it would be an instrument), it follows of necessity that it is moving itself—following the supposition of the Platonists that every mover is moved. Hence also according to this argument, either what is being moved will be immediately moved by a mover that moves itself, or at some time such a mover that moves itself must be reached.
lib. 8 l. 9 n. 6 Deinde cum dicit: ad dicta autem etc.; ostendit quod non omne movens movetur, ut in prioribus rationibus supponebatur. Et circa hoc duo facit: primo probat quod non omne movens movetur; secundo tam ex hoc quam ex superioribus rationibus concludit principale propositum, ibi: non ergo necesse semper moveri et cetera. Dicit ergo primo, quod supra praedicta possunt etiam addi haec ad nostrum propositum ostendendum. Et circa hoc tria facit: primo praemittit quandam divisionem; secundo destruit unam partem, ibi: primum quidem igitur etc.; tertio destruit aliam partem, ibi: at vero si non secundum accidens et cetera. Dicit ergo primo, quod si omne quod movetur, movetur ab eo quod movetur, quod est omne movens moveri, hoc potest esse dupliciter: uno modo quod hoc inveniatur per accidens in rebus ut movens moveatur, ita scilicet quod movens non moveat propter id quod movetur (ut si dicamus aedificatorem esse musicum, non quia musicus est, sed per accidens); aut non est per accidens quod movens moveatur, sed per se.	1042. Then at (810 256 b3) he shows that not every mover is being moved, as was supposed in the preceding arguments. About this he does two things: First he proves that not every mover is being moved; Secondly, from this and from the previous arguments he concludes to his main proposition, at 1049. He says therefore first that to the above-mentioned things may be added the following in order to show our proposition. About this he does three things: First he premises a division; Secondly, he rejects one member$ at 1043; Thirdly, he rejects another, at 1046. He says therefore First (810 256 b3) that if whatever is being moved is being moved by another, which is tantamount to saying that every mover is moved, this can be in two ways: in one way, that it is per accidens in things that a mover is moved, i.e., the mover does not act in virtue of being moved (as if we should say that a musician is a builder not because he is a musician, but this is per accidens); or in a second way, that it is not per accidens but per se that a mover is moved.
lib. 8 l. 9 n. 7 Deinde cum dicit: primum quidem etc., destruit primum membrum tripliciter. Primo quidem tali ratione. Nihil quod est per accidens, est necessarium: quod enim inest alicui per accidens, non ex necessitate inest ei, sed contingit non inesse, sicut musicum aedificatori. Si igitur moventia per accidens moventur, sequitur quod contingat ea non moveri; sed cum tu ponas quod omne movens movetur, consequens est quod si non moventur moventia, quod non moveant; sequitur ergo quod aliquando nihil moveatur. Hoc autem est impossibile, quia ostensum est supra, quod necesse est motum semper esse. Istud autem impossibile non sequitur ex hoc quod supposuimus moventia non moveri: quia si hoc est per accidens quod movens moveatur, moventia non moveri erit possibile; possibili autem posito, nullum sequitur impossibile. Relinquitur ergo quod aliud ex quo sequitur, sit impossibile, scilicet quod omne movens moveatur.	1043. Then at (811 256 b7) he rejects the first member in three ways. First, with this argument: Nothing per accidens is necessary, for what is in a thing per accidens is not present of necessity, but may happen not to be present, as musician in a builder. If, therefore, it is per accidens that movers are moved, it follows that it can happen that they not be moved. But once you posit that every mover is moved, it is a consequence, if movers are not moved, that they do not cause motion. It follows, therefore, that at some time, nothing is being moved. But this is impossible, for it has been proved above that it is necessary that motion always exist. This impossibility, however, does not follow from the supposition that movers are not moved; because if it is per accidens that a mover is moved, it will be possible for movers not to be moved, and if a possibility is posited, no impossibility follows. It remains, therefore, that the other statement from which it (the cessation of motion) followed is impossible, namely, the statement that every mover is moved.
lib. 8 l. 9 n. 8 Secundo ibi: et rationabiliter hoc accidit etc., probat idem alia probabili ratione: quae talis est. In motu tria inveniuntur: quorum unum est mobile quod movetur, aliud autem est movens, tertium est instrumentum quo movens movet. In istis autem tribus manifestum est quod id quod movetur, necesse est moveri, sed non est necesse quod moveat. Instrumentum autem quo movens movet, necesse est et movere et moveri (movetur autem a principali movente, et movet ultimum motum): unde et omne quod movet et movetur, habet rationem instrumenti. Ideo autem instrumentum quo movens movet, et movetur et movet, quia communicat cum utroque, existens in quadam identitate ad id quod movetur. Et hoc maxime manifestum est in motu locali: necesse est enim quod a primo movente usque ad ultimum motum, omnia se tangant ad invicem; et sic patet quod instrumentum medium est idem per contactum cum mobili, et sic simul movetur cum ipso, inquantum communicat ipsi. Sed etiam communicat moventi, quia est movens; hoc modo tamen ut instrumentum quo movet, non sit immobile. Sic igitur ex praemissis apparet quod ultimum motum movetur quidem, sed non habet in se principium movendi neque seipsum neque aliud; et movetur quidem ab alio, sed non a seipso. Unde videtur esse rationabile, idest probabile (nec ad praesens curamus dicere quod sit necessarium), esse aliquod tertium, quod moveat cum sit immobile. Probabile enim est, quod si aliqua duo coniunguntur per accidens, et unum invenitur sine alio, quod etiam aliud inveniatur sine illo (sed quod possit inveniri sine illo, hoc est necessarium; quia quae per accidens coniunguntur, contingit non coniungi): sicut si album et dulce per accidens coniunguntur in zuccaro, et album invenitur sine dulci, ut in nive, probabile est quod et dulce inveniatur in aliqua re sine albo, ut in cassia. Si igitur movens moveri est per accidens, et invenitur moveri absque movere in aliquo, sicut in ultimo moto; probabile est quod inveniatur movere absque moveri, ut sit aliquod movens quod non movetur. Ex quo patet quod ista ratio non habet instantiam in substantia et accidente, et materia et forma, et in similibus, quorum unum invenitur sine alio sed non e converso: accidens enim per se inest substantiae, et materiae per se convenit ut habeat esse per formam.	1044. Secondly, at (812 256 b13) he proves the same with another probable argument, which is this: Three things are found in motion: one is the mobile that is being moved; another is the mover, and the third is the instrument by which the mover causes motion. Now among these three, it is clear that the thing which is moved has to be moved, but it does not have to cause motion. The instrument, however, by which the mover causes motion, must both move and be moved—it is moved by the principal mover and it moves the last thing moved. For this reason, whatever “moves and is moved” has the character of an instrument. Now, the reason why the instrument by which the mover causes motion both is moved and moves is that it partakes of both and exists in a sort of identity to what is moved. This is especially evident in local motion, for it is necessary that from the first mover to the last thing moved, all must touch one another. Accordingly, it is evident that an intermediate instrument is through contact the same as the mobile and is moved at once with it, insofar as it is in union with it. But it is also in union with the mover, because it is a mover—although under its aspect as the instrument by which the mover causes motion, it is not immobile. Accordingly, therefore, it appears from the premises that the last thing moved is, indeed, being moved but it does not have in itself a principle for moving either itself or anything else, and it is moved indeed by something else and not by itself. Hence, it seems to be reasonable, i.e., probable (and in the present case we do not care to say that it is necessary) that there be a third thing which causes motion but is immobile. For it is probable that if two things are joined per accidens, and one is found without the other, then the other might be found without it (but that it may be found without the other is necessary, because things joined per accidens may happen to be not joined); for example, if white and sweet are joined per accidens in sugar, and if white is found without sweet, as in snow, it is probable that sweet be found in some thing without white, as in cheese. If, therefore, it is per accidens that a mover be moved and something is found to be moved without moving something else, as happens in the last thing moved, it is probable that one may find moving without being moved, so that there would be a mover that is not moved. From this it is evident that this argument does not have force in substance and accident, and in matter and form, and in like things, of which one is found without the other but not vice versa; for accident per se exists in a substance, and to matter it belongs per se to have existence through form.
lib. 8 l. 9 n. 9 Tertio ibi: unde Anaxagoras dicit etc., probat idem testimonio Anaxagorae. Quia enim contingit inveniri aliquod movens quod non movetur, ideo Anaxagoras recte dixit, ponens intellectum impassibilem et immixtum. Et hoc ideo, quia ipse ponebat intellectum primum principium motus: sic autem solummodo poterit movere et imperare, absque hoc quod moveatur, si sit immixtus: quod enim commiscetur alteri, movetur quodammodo ad motum ipsius.	1045. Thirdly, at (813 256 b24) he proves the same point on the testimony of Anaxagoras. For since it may be that a mover be found that is not moved, Anaxagoras spoke aright when he said that Mind is impassible and unmingled. He said this because he posited Mind as the first principle of motion, and the only way it could cause motion and command, without itself being moved, was that it be unmingled—for what is mingled with something else is in a certain way moved when that something else is moved.
lib. 8 l. 9 n. 10 Deinde cum dicit: at vero si non secundum accidens etc., prosequitur aliam partem divisionis; scilicet quod omne quod movetur, movetur ab aliquo quod movetur per se et non secundum accidens. Et improbat hoc duabus rationibus: quarum prima talis est. Si hoc non est secundum accidens sed ex necessitate ut movens moveatur, et nunquam possit movere nisi moveatur, oportet hoc contingere duobus modis: quorum unus est ut movens moveatur secundum eandem speciem motus qua movet; alius est ut movens secundum unam speciem motus moveat, secundum alteram moveatur. Exponit autem consequenter primum modum, cum dicit: dico autem et cetera. Sic enim dicimus movens moveri secundum eandem speciem motus, puta si calefaciens calefiat, et sanans sanetur, et ferens secundum locum feratur. Et secundum modum exponit cum dicit: vel sanans feratur, vel ferens augeatur; hoc enim est ut secundum aliam speciem motus moveat et moveatur. Deinde ostendit impossibilitatem primi modi, cum dicit: sed manifestum et cetera. Manifestum est enim impossibile esse quod movens secundum eandem motus speciem moveatur. Non enim sufficiet stare in aliqua specie subalterna, sed oportebit pervenire per divisionem usque ad individua, idest usque ad species specialissimas: puta si aliquis doceat, non solum doceatur, sed idem doceat et doceatur; puta si docet geometriam, quod hoc idem doceatur; aut si movet specie motus localis quae est proiectio, quod secundum eundem motum proiectionis moveatur: et hoc est manifeste falsum. Deinde destruit secundum modum, ut scilicet non moveatur movens secundum eandem speciem motus, sed quod movet uno genere motus, moveatur alio genere: puta quod movet secundum locum, moveatur per augmentum; et quod movet per augmentum, moveatur ab aliquo alio per alterationem; et illud alterans moveatur secundum aliquem alium motum. Manifestum est autem quod motus non sunt infiniti, neque secundum genus neque secundum speciem. Est enim habitum in quinto, quod motus differunt genere et specie secundum differentias rerum in quibus sunt motus: genera autem rerum et species non sunt infinitae, ut alibi probavit; et sic neque genera aut species motus. Si ergo movens necesse est moveri alio genere aut alia specie motus, non erit procedere in infinitum, sed erit aliquod primum movens immobile.	1046. Then at (814 256 b27) he concentrates on the other part of the division, namely, that whatever is moved, is being moved by another which is moved per se and not according to an accident. And he disproves this with two arguments, the first of which is: If it is not according to an accident but of necessity that a mover be moved and if it can never cause motion unless it is moved, this must happen in two ways: one of which is that the mover is moved according to the same species of motion as that which it causes; the other is that the mover moves according to one species of motion, and is moved according to another. He subsequently explains the first way at (815 256 b31): We say that a mover is being moved according to the same species of motion if, for example, the thing that causes heating is heated, and the healer is healed, and something carrying locally is itself being carried locally. He explains the second way when he says: “Or else the healer is carried along, or the thing carrying along is growing.” These are examples of “moving and being moved” according to different species of motion. Then he shows the impossibility of the first way, at (816 256 b34). For it is clearly impossible that a mover be moved according to the same species of motion. For it is not sufficient to stop at some subalternate species, but one Must divide until he reaches the “individuals,” i.e., the most special species. For example, if someone is teaching, it is not enough for him simply to be taught at the same time, but he must be teaching and being taught the same; e.g., if he is teaching geometry he must be at the same time being taught it; or if he is the cause of a local motion called throwing, he must himself be moved according to the same motion of throwing. This is clearly false. Then he dismisses the second ways namely, that the mover not be moved according to the same species of motion, but that it move according to one species and be moved according to another; for example, if it moves with a local motion, and is being moved with respect to growth; and if what causes the growth is being moved by some thing else according to alteration; and if this mover in turn is being moved with respect to some other motion. Now it is clear that motions are not infinite either in genus or species. For it was held in Book V that motions differ in genus and species according to the differences of the species in which motion occurs. But the genera and species of things are not infinite, as we proved elsewhere; accordingly, neither are the genera and species of motion. If, therefore, a mover is necessarily being moved according to some other genus or species of motion, one will not be able to proceed to infinity and there will be some first immobile mover.
lib. 8 l. 9 n. 11 Sed quia posset aliquis dicere, quod quando deficient omnes species motus, iterum redibitur ad primam; ut scilicet si primum motum acceptum movebatur localiter, distributis omnibus generibus et speciebus motuum per diversos motores, motor qui residuus erit movebitur motu locali: ad hoc excludendum consequenter dicit, quod tantum valet sic reflectere, ut dicatur quod alterans feratur (quod dicit, quia motum localem supra prius nominaverat, et alterationem ultimo) sic inquam reflectere idem est ac si statim a principio dicatur quod movens secundum locum movetur; et non solum in genere sed in specie, quod docens docetur. Et quod hoc tantundem valeat, probat consequenter. Omne enim quod movetur, magis movetur a superiori movente quam ab inferiori, et per consequens multo magis a primo movente. Si ergo id quod ponebatur moveri localiter, movetur a propinquo quidem movente quod augetur, ulterius autem ab eo quod alteratur, ultra autem ab eo quod movetur secundum locum: hoc quod movetur secundum locum, magis movebitur a primo quod movetur secundum locum, quam a secundo quod alteratur, aut a tertio quod augetur. Ergo erit verum dicere quod movens secundum locum, movetur secundum locum; et similiter secundum unamquamque speciem motus. Hoc autem non solum est falsum, quia videtur instantiam habere in multis, sed etiam est impossibile. Sequeretur enim quod docens addiscat dum docet; quod est impossibile. Includit enim hoc contradictionem; quia de ratione docentis est quod habeat scientiam, de ratione autem addiscentis quod non habeat. Sic ergo patet quod non est necessarium movens moveri.	1047. But because someone could say that when all the species of motion are exhausted, a return will be made to the first species, in such a way that if the first thing taken as moved was moved locally, and we distributed all the genera and species of motion to different movers until these genera and species were exhausted, the remaining mover will then be moved according to local motion, in order to exclude this he subsequently says that such a return is tantamount to saying that the cause of alteration is being moved locally (he uses this explanation because above in his example he mentioned local motion first and alteration last), the same, I say, as supposing from the very beginning that the mover according to local motion is being moved, and that the teacher is being taught not only generically but in the specific sense. And that this means nothing more, he proves consequently. For whatever is being moved is moved more by the higher mover than by the lower one, and, consequently, much more so by the first mover. If, therefore, the thing posited as being moved locally is being moved by a neighboring mover that is being increased, and it by a mover that is being altered, and it further by one that is being moved according to place, what is being moved according to place will be more moved by the first one moved according to place than by the second one which is being altered or by the third one which is being increased. Therefore it will be true to say that the mover according to place is being moved according to place, and the same for every sphere of motion. Now this is not only false, because it is seen to be belied in many cases, but it is also impossible. For it would follow that the teacher is learning while he is teaching—which is impossible. For this involves a contradiction, since it is the property of a teacher that he have science, and of a learner that he not have it. Accordingly, it is clear that it is not necessary for a mover to be moved.
lib. 8 l. 9 n. 12 Secundam rationem ponit ibi: amplius autem his magis irrationabile etc.: quae non differt a praecedenti nisi in hoc, quod prima deducebat ad quaedam inconvenientia particularia, puta quod proiiciens proiiceretur, aut docens addisceret; haec autem ducit ad inconveniens in communi. Unde dicit quod licet inconveniens sit quod docens addiscat, tamen adhuc est magis irrationabile; quia accidit quod omne motivum sit mobile, si nihil movetur nisi ab eo quod movetur. Sic enim sequetur quod omne movens sit mobile; puta si dicatur quod omne quod habet virtutem sanandi aut quod sanat in actu, est sanabile, et quod habet virtutem aedificandi, est aedificabile: quod est magis irrationabile quam quod docens addiscat; quia docens potuit prius addiscere, sed aedificans nunquam fuit aedificatus. Hoc autem dupliciter sequitur. Si enim detur quod omne movens movetur secundum eandem speciem motus, sequitur quod mox, idest immediate, aedificans aedificetur et sanans sanetur: si autem detur quod non per eamdem speciem motus movens movetur, sequitur quod per plura media tandem in hoc veniatur. Et hoc exponit: quia si omne quod movet movetur ab alio, sed tamen non movetur secundum eundem motum statim quo movet, sed secundum alterum motum; puta si aliquid sit sanativum, non statim ipsum sanetur, sed moveatur motu disciplinae addiscendo: tamen, cum non sint infinitae species motus, sic ascendendo de mobili ad movens, pervenietur quandoque ad eandem speciem motus, sicut supra expositum est. Horum ergo duorum unum apparet manifeste impossibile, puta quod aedificans mox aedificetur; aliud autem videtur esse fictitium, scilicet quod per multa media in hoc veniatur. Inconveniens enim est, quod id quod natum est alterare, ex necessitate sit natum augmentari.	1048. He gives a second argument at (817 257 a14) which does not differ from the preceding one except in that the first leads to certain particular inconsistencies, for example, that a thrower would be thrown or that a teacher would be being taught. But this one leads to inconsistencies in general. Hence he says that although it is inconsistent that a teacher be learning, there is something still more unreasonable, for it turns out that every mover is mobile, if nothing is moved except by what is being moved. For it will thus follow that every mover is mobile, if, for example, one says that whatever has the power to heal, or is actually causing health, is healable, and that whatever has the power to build is buildable—which is more unreasonable than that a teacher be learning, for a teacher could have been learning before, but a builder was never built. Now this follows in two ways. For if it be conceded that every mover is being moved with respect to the same species of motion, it follows that a builder is being built immediately (i.e., without intermediary) and that a healer is being healed immediately. But if it be conceded that the mover is not being moved according to the same species of motion, it follows that we shall finally come to this after passing through a number of intermediates. And he explains this: If every mover is being moved by another but not being moved immediately with respect to the same species in which he is causing motion but according to some other species—for example, if a healer is not at once being healed but is being moved according to the motion of discipline by learning—yet, since the species of motion are not infinite, by thus ascending from mobile to mover one will at length reach the same species of motion, as was explained above. Therefore, of these two, one appears plainly impossible, e.g., that the builder be immediately being built, while the other is seen as a fancy, namely, that one come to the same thing through a number of intermediates. For it is unacceptable that what is apt to cause alteration is of necessity apt to be increased in size.
lib. 8 l. 9 n. 13 Sic ergo consideratis praemissis rationibus, quarum primae concludebant quod non in infinitum hoc procedit, quod omne quod movetur moveatur ab alio; et secundae concludebant quod non omne movens moveatur: possumus ex omnibus praedictis rationibus concludere, quod non est necesse in infinitum quod moveatur ab alio moveri, ita quod semper movetur a movente quod movetur. Ergo necesse est quod stetur in aliquo primo. Hoc autem primum oportet quod vel sit immobile, vel sit movens seipsum. Sed si consideretur quae sit prima causa motus in genere mobilium, utrum illud quod movet seipsum, aut mobile quod movetur ab alio: probabile est apud omnes, quod primum movens sit movens seipsum. Semper enim causa quae est per se, est prior ea quae est per alterum. Et propter hanc rationem Platonici posuerunt ante ea quae moventur ex alio, esse aliquid quod movet seipsum. Et ideo considerandum est de eo quod movet seipsum, facientes ex hoc aliud principium nostrae considerationis: scilicet ut consideremus, si aliquid movet seipsum, quomodo hoc est possibile.	1049. Accordingly, (818 257 a27) having considered the foregoing arguments, the first of which concluded that this process—that whatever is being moved is being moved by another—must not go on ad infinitum, and the second of which concluded that not every mover is being moved, we can conclude from all the foregoing arguments that it is not necessary ad infinitum that what is being moved be moved by another in such a way that it is always being moved by a mover that is being moved. Therefore, it is necessary to stop at some first. However, this first must either be immobile or be moving itself. But if we are considering which is the first cause of motion in the genus of mobiles, whether it is something that moves itself or a mobile that is moved by another, it is held as probable among all that the first mover moves itself. For a per se cause is always prior to what is a cause through another. For this reason, the Platonists held that prior to things that are moved by another there is something that moves itself. And therefore we must consider this thing that moves itself and make of this another beginning of our consideration, namely, that we consider that if something moves itself, how is this possible.