Dist. 14, Part 2, Art. 1, Q. 2
Book II: On the Creation of Things · Distinction 14
Quaestio II. Utrum luminaria in suis orbibus moveantur motibus propriis.
Secundo quaeritur, utrum luminaria moveantur in orbibus suis motibus propriis. Et quod sic, videtur.
Ad oppositum. 1. Aves enim, quae sunt ad ornatum aëris, motu proprio moventur in illo, et pisces in aquis: ergo et pari ratione luminaria in caelis.
2. Item, motus orbium non ponitur nisi propter motum luminarium: quia, circumscripto corpore, de se aequaliter habent influere, sive moveantur sive stent; sed natura non facit per plura quod potest facere per pauciora, nec facit cum maiori difficultate quod potest facere cum minori1: si ergo idem facit motus sideris, quod facit motus totius orbis, videtur, quod naturae sit consonum ponere, quod stellae moveantur propriis motibus.
3. Item, si luminaria moventur motu suorum orbium, cum moveantur motibus disparatis et quasi in oppositum caelo stellato; tunc videtur, quod fiat ibi obviatio et retardatio, cum illud in quo moventur, sit unum corpus continuum.
4. Item, manifeste videmus ad oculum, in planetis esse elevationes et depressiones, progressiones et retrogradationes; sed hoc non posset esse, nisi propriis motibus moveri habeant: ergo etc.
Fundamenta. Sed contra: 1. Si motibus propriis moventur planetae, ergo vel duo corpora erunt in eodem loco, vel necesse est, vacuam esse viam, per quam transit planeta, vel necesse est, corpus caeli rarefieri et condensari, et ita corrumpi: sed quodlibet horum est manifeste impossibile2: ergo etc.
2. Item, «natura non deficit in necessariis3», maxime circa ea quae sunt in ipsa nobiliora: ergo si in his quae moventur motu proprio, providit instrumenta, utpote pedes et alas vel pennas, videtur, quod in caelestibus corporibus debuerit dare ista; sed ista non habent, sicut patet ad sensum: ergo vel natura in eis deficit, vel non moventur motibus propriis.
3. Item, stellae in octava sphaera non moventur nisi motu illius sphaerae: ergo si ita collocatur unusquisque planeta in suo orbe, sicut stellae in octava sphaera, videtur, quod nullum luminare proprio motu habeat moveri.
4. Item, si luminaria aliqua moverentur motu proprio ad faciendum progressionem vel retrogradationem, impossibile esset, motum caeli esse uniformem: si ergo motus est uniformis et perpetuus4, videtur, quod nihil sit, planetas moveri motibus propriis et aliquando retrocedere, aliquando progredi.
Conclusio. Luminaria coeli probabilius non moventur propriis motibus, sed ad motum orbium, in quo ipsa sita sunt.
Respondeo: Dicendum, quod de hac quaestione controversia est inter naturales et mathematicos5.
Opinio mathematicorum. Mathematici enim, maxime considerantes apparentia, ut illa possent salvare simul cum motus
perpetuitate et uniformitate, posuerunt excentricos et epicyclos, et planetas moveri motibus propriis in epicyclis; et secundum hoc, salvata motus uniformitate, aliquando contingit planetam deprimi, aliquando elevari secundum motum ipsius planetae in epicyclo, et epicycli in excentrico, et excentrici circa centrum proprium, quod est extra centrum mundi. — Ad obiectionem autem naturalium de corporis illius continuitate respondent diversimode, dicentes, quod non est inconveniens, si corpus illud scinditur motu planetae, quia est naturae igneae. Alii dicunt, quod corpus illud non scinditur, et planetae pertranseunt; corpus enim lucis simul potest esse cum alio corpore.
Opinio Philosophi et conclusio. Positio vero naturalium est, sicut Aristotelis et Commentatoris, quod planetae non moventur nisi motu suorum orbium, sicut clavus fixus in rota movetur motu rotae, non proprio; et hoc ponunt propter illius corporis incorruptibilitatem, propter quam non potest scindi nec transitum praebere alii corpori. Ponunt etiam, idem esse centrum orbium superiorum et inferiorum, scilicet centrum mundi, propter rotunditatem perfectam ipsorum orbium, qui circulariter moventur, ita quod unus non subintrat alterum. Ponunt etiam cum hoc maiorem et minorem velocitatem in orbibus; et ex hoc habere modo retrogradationes, modo progressiones, quia, cum unum corpus multum praecedit alterum sua velocitate, alterum videtur retrocedere. Et haec omnia valde videntur rationi consona.
Iudicium de his. Et ideo, licet positio mathematicorum secundum iudicium sensuum videatur esse verior, quia secundum illam viam procedendo et iudicando non falluntur circa motus corporum superiorum; secundum rem tamen non oportet esse verius, quia falsum frequenter est via inveniendi verum; sed rationabilius videtur procedere et ponere naturalis philosophus. — Ideo si illam positionem sustinere velimus, potest responderi ad ea quae obiiciuntur in oppositum.
Solutio oppositorum. 1. Ad illud enim quod obiicitur, quod aves in aëre, et pisces in aquis motibus propriis moventur; dicendum, quod non est simile, quia tam aër quam aqua sunt corpora, quae possunt rarefieri et condensari. Et praeterea, ista elementa non sunt sic nata moveri, ut corpora, quae ad eorum ornatum spectant, ipsorum6 motu sufficienter possint transmutari localiter, secundum quod exigit decor universi. Praeterea, ipsis animalibus competit motus progressivus propter sui indigentiam, et qui est ad assequendum aliquod delectabile; et hoc in luminaribus caeli nec competere potest nec debet.
2. Ad illud quod obiicitur, quod motus orbium est propter motum luminarium; dicendum, quod verum est; tamen ex hoc non sequitur, quod sola luminaria debeant moveri. Non enim sic salvatur integritas corporis quinti, si stellae moveantur motibus propriis, sicut si moveantur in orbibus suis, quia ibi per talem motum corporum caelestium non fit aliqua mutatio de loco ad locum secundum totalitatem mobilis, sed circa locum, nec alicuius corporis divisio; et hoc totum perfectio et incorruptibilitas caeli exigebat.
3. Ad illud quod obiicitur, quod, si moventur motu orbium, videtur, quod sit retardatio et obviatio; dicendum, quod non est obviatio, nisi quando directe secundum eandem lineam corpora moventia sibi obviant. Hic autem non est sic, quia orbes inferiores sunt sub superioribus; ideo motus eorum eis non repugnat nec etiam retardat propter maximam mobilis ad motorem obedientiam.
4. Ad illud quod obiicitur de illis retrogradationibus et progressionibus, dicendum, sicut tactum est, quod etsi videantur fieri ad sensum, hoc non est nisi propter maiorem et minorem velocitatem ipsorum orbium, quam si quis bene sciret explicare, hac via unica posset salvare illud, ad quod salvandum mathematici ponunt circulorum et centrorum multitudinem: sed hoc ad aliam scientiam spectat7.
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Question II. Whether the luminaries are moved in their own orbs by their own motions.
Secondly it is asked whether the luminaries are moved in their orbs by their own motions. And that they are so, seems [the case].
To the opposed view. 1. For birds, which are for the adornment of the air, are moved in it by their own motion, and fishes in the waters: therefore by parallel reasoning the luminaries also in the heavens.
2. Likewise, the motion of the orbs is not posited except on account of the motion of the luminaries: for, the body being set aside, of themselves they have power to influence equally, whether they be moved or stand still; but nature does not do through many what it can do through fewer, nor does it do with greater difficulty what it can do with less1: if therefore the motion of the star does the same as the motion of the whole orb does, it seems that it accords with nature to posit that the stars are moved by their own motions.
3. Likewise, if the luminaries are moved by the motion of their orbs, since they are moved by disparate motions and as if contrary to the starry heaven, then it seems that there would be there meeting and retardation, since that in which they are moved is one continuous body.
4. Likewise, we manifestly see by sight, that in the planets there are elevations and depressions, progressions and retrogradations; but this could not be, unless they had to be moved by their own motions: therefore etc.
The foundations. On the contrary: 1. If the planets are moved by their own motions, then either two bodies will be in the same place, or it is necessary that the way by which the planet passes be empty, or it is necessary that the body of the heaven be rarefied and condensed, and so corrupted: but any of these is manifestly impossible2: therefore etc.
2. Likewise, «nature does not fail in necessaries3», especially with respect to those things that are nobler in itself: therefore if for those things which are moved by their own motion, it provided instruments, namely feet and wings or pinions, it seems that it ought to have given these to the celestial bodies; but they do not have them, as is plain to sense: therefore either nature fails in them, or they are not moved by their own motions.
3. Likewise, the stars in the eighth sphere are not moved except by the motion of that sphere: therefore if each planet is so placed in its orb, just as the stars in the eighth sphere, it seems that no luminary has [the power] to be moved by its own motion.
4. Likewise, if any luminaries were to be moved by their own motion to make progression or retrogradation, it would be impossible that the motion of the heaven be uniform: if therefore the motion is uniform and perpetual4, it seems that there is nothing to it that the planets are moved by their own motions and sometimes retrocede, sometimes progress.
Conclusion. The luminaries of heaven, more probably, are not moved by their own motions, but to the motion of the orbs in which they themselves are set.
I respond: It must be said that on this question there is controversy between the natural philosophers and the mathematicians5.
Opinion of the mathematicians. For the mathematicians, considering above all the appearances, that they might save them together with the perpetuity and uniformity of motion, posited eccentrics and epicycles, and that the planets are moved by their own motions in the epicycles; and according to this, the uniformity of motion being preserved, sometimes it happens that the planet is depressed, sometimes elevated according to the motion of the planet itself in the epicycle, and of the epicycle in the eccentric, and of the eccentric about its own center, which is outside the center of the world. — But to the objection of the natural philosophers concerning the continuity of that body, they respond in various ways, saying that it is not unfitting if that body is split by the motion of the planet, since it is of fiery nature. Others say that that body is not split, and the planets pass through; for the body of light can be together with another body.
Opinion of the Philosopher and conclusion. But the position of the natural philosophers is, as of Aristotle and the Commentator, that the planets are not moved except by the motion of their orbs, just as a nail fixed in a wheel is moved by the motion of the wheel, not by its own; and they posit this on account of the incorruptibility of that body, on account of which it cannot be split nor afford passage to another body. They posit also that the center of the higher and lower orbs is the same, namely the center of the world, on account of the perfect roundness of those orbs themselves, which are moved circularly, so that one does not enter under the other. They posit also together with this a greater and lesser velocity in the orbs; and from this [that they] have now retrogradations, now progressions, because, when one body much precedes another by its velocity, the other seems to retrocede. And all these things seem very consonant to reason.
Judgment about these. And therefore, although the position of the mathematicians according to the judgment of the senses seems to be truer, because proceeding and judging in that way they are not deceived concerning the motions of the higher bodies; according to the thing however it need not be truer, because the false is frequently a way of finding the true; but the natural philosopher seems to proceed and posit more reasonably. — Therefore, if we should wish to sustain that position, it can be replied to those things which are objected on the opposite side.
Solution of the opposed [arguments]. 1. To that, then, which is objected, that birds in the air and fishes in the waters are moved by their own motions; it must be said that it is not similar, because both air and water are bodies which can be rarefied and condensed. And besides, these elements are not so constituted by nature to be moved, like the bodies which pertain to their adornment, that by their6 motion [those bodies] can be sufficiently transmuted locally, according to what the beauty of the universe demands. Besides, to animals themselves progressive motion belongs on account of their indigence, and which is for attaining some delectable thing; and this neither can nor ought to belong to the luminaries of heaven.
2. To that which is objected, that the motion of the orbs is on account of the motion of the luminaries; it must be said that it is true; nevertheless from this it does not follow that the luminaries alone ought to be moved. For the integrity of the fifth body is not so preserved, if the stars are moved by their own motions, as if they are moved in their orbs, because there through such motion of celestial bodies there is no change from place to place according to the totality of the mobile, but about a place, nor any division of any body; and the whole perfection and incorruptibility of heaven required this.
3. To that which is objected, that, if they are moved by the motion of the orbs, it seems that there is retardation and meeting; it must be said that there is no meeting, except when bodies in motion meet one another directly along the same line. But here it is not so, because the lower orbs are under the higher; therefore their motion is not repugnant to them nor even retards [them], on account of the very great obedience of the mobile to the mover.
4. To that which is objected concerning those retrogradations and progressions, it must be said, as has been touched on, that although they seem to come about to sense, this is only on account of the greater and lesser velocity of the orbs themselves, which if anyone knew well how to explain, by this single way he could save that for the saving of which the mathematicians posit the multitude of circles and centers: but this pertains to another science7.
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- Vide supra pag. 44, nota 5. — Aristot. hanc quaestionem proponit II. de Caelo et mundo, text. 43–52. (c. 8.), ubi etiam insinuantur plura argg. quae hic afferuntur.See above p. 44, note 5. — Aristotle proposes this question, On the Heavens and the World II, text 43–52 (c. 8), where also several of the arguments which are here adduced are insinuated.
- Cfr. supra pag. 324, nota 9. et hic p. I. dub. 2.Compare above p. 324, note 9, and here pars I, dubium 2.
- Aristot., III. de Anima, text. 45. (c. 9.). Cfr. II. de Caelo et mundo, text. 50. et 59. (c. 8. et 11.), ubi etiam dicitur, quod stella non movetur motu proprio, propterea quod nullum habet organum ad motum.Aristotle, On the Soul III, text 45 (c. 9). Compare On the Heavens and the World II, text 50 and 59 (c. 8 and 11), where also it is said that the star is not moved by its own motion, because it has no organ for motion.
- Ut ponit Aristot., II. de Caelo et mundo, text. 35. seqq. (c. 6.). — Paulo inferius plures codd. non sit, cod. Q non sit ponere, cod. cc et ed. 1 non sinit pro nihil sit.As Aristotle posits, On the Heavens and the World II, text 35 ff. (c. 6). — A little below, several codices [read] non sit, codex Q non sit ponere, codex cc and edition 1 non sinit in place of nihil sit.
- Vide Aristot., II. de Caelo et mundo, cum Comment. Averrois, text. 35. 47. 58. seq. (c. 6. 8. 10.); III. text. 61. (c. 7.); I. Metaph. text. 19. seqq. et XII. text. 44. seqq. (l. c. 8. et XI. c. 8.), ubi etiam sententia Aristotelis et Averrois, de qua paulo inferius mentio fit, invenitur. — Epicyclus, a Graeco ἐπί i. e. in vel super, et κύκλος i. e. circulus, est circulus in alio circulo vel super alium circulum; et mathematici hoc termino nominant orbiculum, per cuius circumferentiam planeta defertur, ipsumque ponunt propter varios planetarum motus, ad quos explicandos non sufficit circulus excentricus in planetis, praeter solem.See Aristotle, On the Heavens and the World II, with the Commentary of Averroes, text 35, 47, 58 ff. (c. 6, 8, 10); III, text 61 (c. 7); Metaphysics I, text 19 ff. and XII, text 44 ff. (l. c. 8 and XI c. 8), where also the opinion of Aristotle and of Averroes, which is mentioned a little below, is found. — Epicyclus, from the Greek ἐπί i.e. in or upon, and κύκλος i.e. circle, is a circle in another circle or upon another circle; and the mathematicians name by this term the small orb through whose circumference the planet is carried, and they posit it on account of the various motions of the planets, for explaining which the eccentric circle in the planets, besides the sun, does not suffice.
- Vat. quae ipsorum. Aliquando inferius plures codd. et hic pro et hoc.The Vatican edition [reads] quae ipsorum. Sometimes below several codices [read] et hic in place of et hoc.
- Vide scholion ad praecedentem quaest.See the scholion to the preceding question. ---