Authors/Thomas Aquinas/physics/L4/lect11

Lecture 11 From motion there is shown to be no separated void

Latin	English
	Lecture 11 From motion there is shown to be no separated void
lib. 4 l. 11 n. 1 Positis opinionibus aliorum de vacuo, et quid significetur nomine vacui, hic incipit inquirere veritatem. Et primo ostendit vacuum non esse separatum; secundo ostendit vacuum non esse corporibus inditum, ibi: sunt autem quidam et cetera. Circa primum duo facit: primo ostendit vacuum separatum non esse, ex parte motus; secundo ex consideratione qua ipsum vacuum consideratur secundum se, ibi: et per se autem et cetera. Circa primum duo facit: primo ostendit vacuum non esse ex parte motus; secundo ex parte velocitatis et tarditatis in motu, ibi: amplius autem et ex his et cetera.	520. Having gone over others’ opinions about the void and having indicated what is meant by the word “void,” he now begins to search for the truth. First, he shows that the void does not have a separate existence; Secondly, that there is no void in bodies at no. 544 (L.14). Concerning the first he does two things: First he used motion to show that a separate void does not exist; Secondly, by considering the void in itself, at no. 541. As to the first he does two things: First, from the fact of motion he shows there is no void; Secondly from the fact of faster and slower motions, at no.527 (L.12).
lib. 4 l. 11 n. 2 Circa primum ponit sex rationes. Circa quarum primam dicit quod oportet iterum dicere quod non est vacuum separatum, sicut quidam dicunt. Ideo autem apponit iterum, quia hoc etiam aliqualiter ostensum est ex parte loci: si enim locus non sit spatium, sequitur quod vacuum nihil sit, ut supra dictum est. Sed nunc iterum idem ostendit ex parte motus: ponebant enim vacuum, ut dictum est, propter motum. Sed propter motum non est necessarium ponere vacuum. Maxime enim videtur quod esset causa motus localis: sed propter motum localem non oportet ponere vacuum, quia omnia corpora simplicia habent motus locales naturales, sicut motus naturalis ignis est sursum, et motus terrae est deorsum et ad medium. Et sic manifestum est quod natura uniuscuiusque corporis est causa motus localis, et non vacuum. Quod quidem esset, si propter necessitatem vacui aliqua corpora naturalia moverentur. Si autem non ponitur causa motus localis, nullius alterius motus causa poni potest, neque alterius rei. Frustra igitur vacuum esset.	521. In regard to the first point he gives six reasons. In regard to the first of which he says [360 214 b12] that we must repeat that there is no separated void as some assert. He says “repeat,” because this was already somewhat proved from the notion of place: for if place is not space, it follows that the void is nothing, as was said above. But now he proves the same point again from motion: for void was posited, as we said, on account of motion. But motion does not necessarily require a void. For it would seem especially to be the cause of local motion. But it is not necessary to posit a void in order to explain local motion, because all simple bodies have natural local motions, as the natural motion of fire is upward and that of earth downward toward the center. Thus it is clear that it is the nature of each body that causes its local motion and not the void. The latter would be the cause if any natural bodies were moved due to the necessity of a void. But if it is not set down as the cause of local motion, it cannot be considered the cause of any other motion or of any other thing. The void therefore would exist without a purpose.
lib. 4 l. 11 n. 3 Secundam rationem ponit ibi: amplius, si est etc.: quae talis est. Si ponatur vacuum esse, non potest assignari causa motus naturalis et quietis naturalis. Manifestum est enim quod corpus naturale movetur ad locum suum naturalem et quiescit in eo naturaliter, propter convenientiam quam habet cum ipso, et quia non convenit cum loco a quo recedit. Sed vacuum non habet aliquam naturam per quam possit convenire vel disconvenire a corpore naturali. Si ergo ponatur aliquod vacuum, quasi quidam locus privatus corpore, non poterit assignari ad quam partem illud corpus naturaliter moveatur. Non enim potest dici quod feratur ad quamlibet partem, quia hoc videmus ad sensum esse falsum, quia ab una parte naturaliter recedit, et naturaliter accedit ad aliam. Et haec eadem ratio valet contra eos qui ponunt locum esse quoddam spatium separatum, in quod corpus mobile fertur. Non enim erit assignare quomodo corpus positum in tali loco, vel moveatur vel quiescat: quia dimensiones spatii nullam habent naturam per quam possit attendi similitudo vel dissimilitudo ad corpus naturale. Et merito congruit eadem ratio de vacuo et de sursum et deorsum, idest de loco, cuius partes sunt sursum et deorsum. Quia illi qui ponunt vacuum, dicunt ipsum esse locum. Et non solum ponentes vacuum, et ponentes locum esse spatium, non possunt assignare quomodo aliquid moveatur et quiescat secundum locum: sed etiam non possunt convenienter assignare quomodo aliquid sit in loco vel in vacuo. Si enim locus ponatur esse spatium, oportet quod totum corpus inferatur in illud spatium; et non sicut accidit apud ponentes locum esse terminum corporis continentis, quod locatum est in loco sicut in aliquo separato, et sicut in quodam corpore continente et sustentante. Et hoc videtur esse de ratione loci, quod aliquid sit in loco sicut in separato et seorsum existente: quia si pars alicuius corporis non ponatur seorsum ab ipso corpore, non erit in eo sicut in loco, sed sicut in toto. Est igitur de ratione loci et locati, quod locus seorsum sit a locato. Et hoc non accidit si spatium sit locus, in quod totum mergitur totum corpus. Non igitur spatium est locus. Et si spatium non est locus, manifestum est quod vacuum non est.	522. He then gives the second reason [361 214 b17]. If a void be postulated, no reason can be assigned for natural motion and rest. For it is clear that a natural body is moved toward its own natural place and rests there naturally on account of the kinship it has with its place and because it has no kinship to the place from which it departs. But the void has no nature by which it could be akin or hostile to a natural body. Therefore, it there were a void, considered as a certain place without a body in it, one could not assign any part to which the body would be naturally moved. For we cannot say that it would be borne to just any part, because observation shows that this is wrong, for a body naturally goes from one place and naturally approaches another. This same reason is valid against those who posit place as a separate space into which a mobile body is borne. For it would be impossible to explain how a body in such a place could either be moved or be at rest: for the dimensions of space have no nature to which a natural body could be similar or dissimilar. Deservedly, then, the same argument applies to the void as to “up” and “down,” i.e., to place, whose parts are “up” and “down”; for those who posit a void call it place. Moreover, not only are those who posit a void and those who posit place to be space unable to explain how something is moved and at rest In respect to place, but also how something exists in place or in the void. For if place is supposed to be space, then the whole body would have to be enclosed inside that space, and not as happens with those who agree that place is the boundary of the containing body and that a thing is in place as in something separate and as in a body that contains and sustains it. Indeed, it seems to be of the very nature of place that something be in place as in something separated and existing apart from it: for if any part of a body is not laid down as separated from the body, it will exist in that body not as in a place but as in the whole. Therefore, it pertains to the very nature of place and of the thing in place that one be separated from the other. But this does not happen if place is space into whose entirety the entice body is immersed. Therefore space is not place. And if space is not place it is clear that no void is place.
lib. 4 l. 11 n. 4 Tertiam rationem ponit ibi: accidit autem dicentibus et cetera. Et dicit quod, cum antiqui philosophi ponerent quod necesse est vacuum esse si est motus, e converso accidit: quia si est vacuum, non est motus. Et hoc probat per quoddam simile. Quidam enim dixerunt quod terra quiescit in medio propter similitudinem partium circumferentiae undique: et sic terra, cum non habeat quare moveatur magis versus unam partem circumferentiae quam versus aliam, quiescit. Et eadem ratione necesse est in vacuo quiescere. Non enim est assignare quare magis moveatur, ad unam partem quam ad aliam: quia vacuum, inquantum huiusmodi, non habet differentias in suis partibus; non entis enim non sunt differentiae.	523. He gives the third reason [362 214 b28] saying that, whereas the early philosophers claimed that the void had to be, if motion existed, the very opposite is the case: for if there were a void there would be no motion. And this he proves by a simile. For some have said that earth comes to rest at the center on account of the likeness of the parts on the whole circumference: consequently, earth, having no reason to be moved toward one part of the circumference more than another, rests. The same reason would cause rest in a void. For there would be no reason for earth to be moved to one part rather than to another, since the void, as such, does not have differences among its parts—for non-being does not possess differences.
lib. 4 l. 11 n. 5 Quartam rationem ponit ibi: deinde quoniam omnis motus etc.: quae talis est. Motus naturalis est prior violento, cum motus violentus non sit nisi quaedam declinatio a motu naturali. Remoto ergo motu naturali, removetur omnis motus; cum remoto priori, removeatur posterius. Sed posito vacuo, removetur motus naturalis; quia tollitur differentia partium loci, ad quas est motus naturalis, sicut et posito infinito, ut supra dictum est. Sed hoc interest inter vacuum et infinitum, quia posito infinito, nullo modo potest poni neque sursum neque deorsum neque medium, ut in tertio dictum est: posito autem vacuo, possunt haec quidem poni, sed non quod ad invicem differant; quia nullius et non entis, et per consequens vacui, cum sit non ens et privatio, non est aliqua differentia. Sed loci mutatio naturalis requirit locorum differentiam, quia diversa corpora ad diversa loca moventur. Unde oportet loca naturalia differre ad invicem. Si igitur ponatur vacuum, nullius erit naturalis loci mutatio. Et si non est loci mutatio naturalis, nulla loci mutatio erit. Unde si est aliqua loci mutatio, oportet quod vacuum non sit.	524. He gives the fourth reason [363 215 a1]as follows. Natural motion is prior to compulsory since compulsory motion is only a departure from natural motion. Therefore, remove natural motion and all other motion is removed; for when the prior is removed, all that follows is removed. But if the void is posited, natural motion is removed; because the differences among the parts of place would be taken away and it is toward such parts that natural motions tend The same holds if the infinite be posited, as we said above. There is, however, this difference between the void and the infinite, that after granting the infinite there is no way of positing “up” or “down” or “center,” as we pointed out in Book III; but after granting a void, these places could be posited, but it would not be because they were mutually different: for no difference can be assigned in the realm of nothing and non-being and, consequently, of the void, which is a non-being and a privation. Yet natural changes of place do require difference of place, because diverse bodies are moved to diverse places. Consequently, natural places must be different one from the other. Therefore, if a void be posited, nothing could undergo a natural change of place; and if there is no natural change of place, there will be no change of place of any sort. Hence, if there is any change of place, there can be no void.
lib. 4 l. 11 n. 6 Quintam rationem ponit ibi: amplius, nunc quidem proiecta et cetera. Circa quam considerandum est quod solet esse quaedam dubitatio circa ea quae proiiciuntur: oportet enim movens et motum simul esse, ut infra in septimo probatur; et tamen illud quod proiicitur, invenitur moveri etiam postquam separatum est a proiiciente, sicut apparet in lapide proiecto, et sagitta emissa per arcum. Nunc igitur supposito quod vacuum non sit, solvitur ista dubitatio ex parte aeris, quo medium repletur. Et hoc dupliciter. Dicunt enim quidam quod ea quae proiiciuntur, moventur etiam postquam non tanguntur a proiiciente, propter antiperistasim, idest repercussionem vel contra-resistentiam: aer enim motus repercutitur ad alium aerem, et ille ad alium, et sic deinceps; et per talem repercussionem aeris ad aerem movetur lapis. Alii vero dicunt quod hoc ideo est, quia aer, qui continuus existens a proiiciente impellitur, velocius impellit corpus proiectum, quam sit motus quo corpus proiectum fertur naturaliter in proprium locum. Unde propter velocitatem motus aeris non permittitur corpus proiectum, ut puta lapis vel aliud huiusmodi, cadere deorsum; sed fertur secundum impulsionem aeris. Nulla autem istarum causarum posset poni, si esset vacuum; et ita corpus proiectum nullo modo ferretur nisi quandiu veheretur, puta a manu proiicientis, sed statim emissus a manu caderet; cuius contrarium videmus. Non ergo est vacuum.	525. The fifth reason is then given [364 215 a14]. In regard to this it should be considered that some question exists about projectiles: for the mover and the thing moved must be always together, as will be proved below in Book VII (1-3). Yet a projectile is found to be in motion even after it is separated from the projector, as is evident in the case of a stone that is thrown, or of an arrow shot from a bow. Now on the supposition that there is no void this difficulty is solved by attending to the air with which the medium [the field of trajectory] is filled. And it is solved in two ways. For some assert that projectiles remain in motion even after they are no longer contact with what gave them impulse on account of antiperistasis, i.e., repercussion or counter-resistence: for the air that has been pushed, pushes against other air, and that against other air, and so on, and it is on account of this impact of air against air that the stone is moved. The other explanation is that the continuum of air that received the impact from the projector pushes the impelled body with more speed than the speed of the motion by which the projectile is naturally borne to its proper place. Hence the speed of the air movement prevents the projectile, for example, the stone, or some other such, from falling downward; but it is carried along by the impulse of the air. Now neither of these explanations could be alleged if there were a void; consequently, a projectile could be moved only as long as it was carried, for example, in the hand of the one casting it: but as soon as it was released from the hand it would fall. But it is the opposite that happens. Therefore, there is not a void.
lib. 4 l. 11 n. 7 Sextam rationem ponit ibi: amplius nullus utique etc.: quae talis est. Si motus sit in vacuo, nullus poterit assignare causam propter quid illud quod movetur, alicubi stat. Non enim est ratio quare magis quiescat in una parte vacui quam in alia; neque in his quae moventur naturaliter, cum non sit differentia in partibus vacui, ut supra dictum est; neque in his quae moventur motu violento. Nunc enim dicimus quod cessat motus violentus, ubi deficit repercussio vel impulsio aeris, secundum duas causas assignatas. Oportebit ergo quod vel quiescat omne corpus, et nihil moveatur; aut si aliquid moveatur, quod movetur in infinitum, nisi occurrat ei aliquod corpus maius, quod violentum motum eius impediat. Ad confirmationem autem huius rationis, subiungit causam quare ponunt aliqui motum fieri in vacuo; quia scilicet vacuum cedit, et non resistit mobili; unde cum vacuum similiter cedit ex omni parte, feretur in infinitum ex qualibet parte.	526. He then gives the sixth reason [365 215 a19]. If motion were in a void, no one could give a reason why the moving object should stop anywhere. For there is no reason why it should stop at one part of the void rather than another. This is true both in the case of objects that are moved naturally, because there is no difference among the parts of the void, as we have said, and in the case of objects moved by a compulsory motion. For now we say that a violent compulsory motion ceases when repercussions or impulsions of the air are lacking, on account of the two reasons already given. Therefore it will have to be admitted either that every body is at rest and nothing in motion or that, if anything be in motion, it will remain In motion to infinity unless it runs into a more powerful body that could impede its compulsory motion. In support of this reasoning, he gives the reason why some posit motion in the void. It is because the void yields to and does not resist the mobile; hence since the void yields in the same way, in all directions, a mobile thing should be moved in all directions ad infinitum.