Commentaria in Summam contra Gentiles, Liber III

From what was said in the preceding chapter, St. Thomas derives this corollary, ¹ that The first motive principle of the motion of heaven is something intellective. Concerning this, moreover, he does two things: first, he shows the proposition; second, he removes certain doubts. ²

I. As to the first, he argues first thus. A heavenly body, according as it acts through its motion, intends the ultimate form, which is the human intellect, which indeed is higher than every form, namely, an informing form. Therefore it does not act toward generation through its own species as a principal agent, but according to the species of some higher intellectual agent, of which it is the instrument. Therefore it is moved by some intellectual substance.

The first consequence is proved. Because nothing acting according to its own species intends a form higher than its own form: since every agent intends what is similar to itself. — The second consequence is proved. Because heaven acts toward generation according as it is moved.

It must be observed that for an agent to act according to its own species is for its nature and form to be for it the principal reason of acting. For we say that a horse according to its own species generates a horse, because the nature of the horse is for it the principal reason of generating, and the horse's own power is the principal cause of such generation. When, therefore, it is said that heaven does not act toward generation according to its own species, it is understood that the nature and form of heaven is not for it the proper and principal reason and power by which it acts toward generation: but some intellectual power, by which it is moved, is that by whose power it acts toward generation, as its instrument.

II. Second. The body of heaven is moved by something. Therefore either that is united to it, so that the composite of heaven and the mover is said to move itself: or it is extrinsic to it. If the first, therefore heaven is animate: since everything that moves itself is living and animate. Not with a nutritive soul: since in it there is no generation and corruption. Not a sensitive one: since it does not have a diversity of organs. Therefore an intellective one.

Therefore etc. — If the second, either that mover will be corporeal: or incorporeal. If corporeal, it will be necessary for it to be moved by another: and since there is no infinite regress in bodies, namely essentially ordered ones, it will be necessary to arrive at a first incorporeal mover. But that which is completely incorporeal is intellectual, as is clear from what went before. Therefore etc. — The same follows if it is posited to be moved immediately by an incorporeal mover.

III. Third. Just as heavy and light bodies are simple, so also are heavenly bodies. Therefore, if they are moved by nature, they will be moved as those are. But those are moved by the generator and the remover of an obstacle, not however in such a way that the form in them is the mover and the matter the moved: since nothing is moved except a body. Therefore heavenly bodies will also be moved similarly. But this is impossible: since they are ingenerable, as not having contrariety; and their motion cannot be hindered. Therefore they are moved by movers through apprehension. Not through sensitive apprehension. Therefore through intellective apprehension.

2. Concerning that reason, by which it is proved that heavy and light things are moved by the generator and the remover of an obstacle, namely because they cannot be moved in such a way that the form is the mover and the matter the moved, there is a doubt. For it could be answered, as some answer who say that bodies of this kind are moved by themselves, that they are not moved by themselves in such a way as if the form taken precisely were the mover and the matter were the moved, but because the whole is the mover and the whole is the moved: but it is true that the whole is the mover by reason of the form, namely because the form is for it the principle by which it moves; it is however moved by reason of the matter, so that the matter is for it the principle by which it is moved. And thus it is established that both the mover and the moved are a body.

But that this response does not satisfy is shown from the words and intention of the Commentator in VIII Phys., comm. 30, ³ from whom St. Thomas took this reason. For there he proves that simple bodies are not moved by themselves, because none of them can be divided into a mover and a moved; and that a simple body cannot be said to be divided into a mover and a moved from the fact that it is divided into matter and form, since, he says, prime matter is not existing in act. For it is clear from these words that for something to be said to move itself per se, it is not sufficient for it to be divided into act and potency, by one of which it is a mover as by a reason of moving, by the other however it is moved as by a reason by which it is moved: but it is required that it be divided into two parts of which each is a being in act, and one is the mover, the other however the moved. And thus, since a simple body cannot be divided into parts of this kind, it is manifest, as St. Thomas deduces, that it does not move itself: namely per se, although per accidens it can move itself, namely with the motion of that which is moved by it, just as a sailor is moved per accidens with the motion of the ship. Concerning which mode of moving Averroes intends when he says, III Caeli, comm. 28, ⁴ and IV Caeli, comm. 2, ⁵ that a stone moves itself inasmuch as it is heavy in act, and is moved inasmuch as it is in potency below. For he holds that a heavy thing, from the fact that it is heavy in act, moves the medium per se; but at the motion of the medium, it is moved by itself per accidens, inasmuch as it is in potency to the place below; just as a sailor, who per se moves a ship inasmuch as he has motive power, is moved per accidens by himself at the motion of the ship, inasmuch as he is in potency to the place to which the ship arrives by its motion.

IV. Fourth. If the motion of heaven were not through apprehension, but were from nature alone, its principle would be the form of heaven: as in the elements, whose forms, although they are not movers, are nonetheless principles of motions, since natural motions follow upon them, just as do other natural properties. But this is impossible. Because form is a principle of local motion inasmuch as some place is due to a body, into which it is moved by the power of its form: as is clear in fire. But to a heavenly body according to its form one "where" is no more suitable than another. Therefore etc.

2. Concerning the motion of heavy and light things, it must be observed first, that the form is said not to be a mover, but a principle of motion, because it is not a principal mover, as a mover which moves: but it is that by which the generator moves, and is the principle by which the moved thing itself is moved.

It must be observed secondly, that from the words of St. Thomas in this reason is had the understanding of his position explained above ⁶ concerning the motion of heavy and light things. For from the fact that the natural motions of these bodies are said to follow upon their forms just as other properties do; and that form is a principle of motion inasmuch as some place is due to a body, into which it is moved by the power of the form tending into that place; likewise that, because the generator gives such a form, it is therefore said to be the mover: it is given to be understood that the generator is not therefore said to move bodies of this kind as if by a new motion and a new impulse it propels them to their places, but because it gave them forms upon which, obstacles being removed, such motions follow through a certain natural resultancy. For from this it follows that both forms and such motions must be reduced to the same cause: just as the form and other properties naturally following the form are reduced to the same cause.

3. Concerning that which is said, that to a heavenly body one where is no more suitable than another according to its nature, it must be observed that St. Thomas well added, according to its nature. For some place is said to be suitable to a body according to its nature when the nature of the thing is perfected in the place so that outside its place it does not have the complement of its perfection: just as it belongs to fire according to its nature to be up, because in the place up it is preserved, and is more perfectly and more actually perfected in its properties. But this is not found in a heavenly body, namely that the substance of heaven receives any perfection from place: since it is not preserved by place. Therefore according to its nature one place is no more suitable to it than another. Inasmuch however as it is ordered to the generation of things, as is said in the Fourth Book of the Sentences, d. XLVIII, where cited above, ⁷ one place is more suitable to it than another: because through its presence and proximity to certain bodies it causes some effect which it does not cause when it is absent.

V. Fifth. ⁸ If the motion of heaven were from nature alone, it would be ordered to some rest. But the contrary of this appears: since it is continuous. Therefore etc. — The consequence is proved. Because, since nature always tends to one thing unless it is hindered, that which has difformity cannot be the end of nature. But motion has difformity: because what is moved is disposed dissimilarly now and previously. ⁹ Therefore motion cannot be the end to which nature tends, but it intends rest through motion, which is compared to motion as one to many: for that rests which is disposed similarly now and previously.

Concerning the proof of the falsity of the consequent, it must be observed that for some motion to be continuous can be understood in two ways. In one way, because its parts are joined to one common term. And thus St. Thomas does not take it in this place: because it is not incompatible for some motion to be continuous in this way, and yet to be ordered to some rest; as is clear concerning the motion of a heavy thing, which is continuous, and is ordered to rest in the place below. — In another way, because it is persevering and never interrupted by rest. And thus it is taken here. For a motion that never has a term in act is not ordered to rest: because a motion ordered to rest at some time ceases, namely through the succession or arrival of rest. Whence, since the motion of heaven is never terminated in act, but one circulation is continued with another circulation; and, according to the philosophers, such motion is never going to cease; ¹⁰ it is established that it is ordered to no rest.

2. Concerning that proposition, That rests which is disposed similarly now and previously, it must be considered that it is understood of the now and the previous of the time measuring the rest: not however of the previous of the time preceding it. So that the sense is that, any two instants of the time measuring the rest of something having been taken, in them that which rests is in the same disposition.

Whether however something can rest in some whole time, and yet in the last instant of that time be disposed otherwise: — it is said, according to the doctrine of St. Thomas in the First Part, q. LIII, a. 3, that it cannot. For there, because it is of the ratio of rest that what is resting is not disposed otherwise now than previously, he concludes that in any now of the time measuring rest, that which is resting is in the same, that is in the same disposition, namely in the first, in the middle, and in the last instant. For he holds it to be impossible that something should rest in some whole time, as in the adequate measure of rest, and yet in the last instant of it be under another disposition and form, since to rest in some whole time in something is to be in it in every instant of that time. The reason for this, moreover, as can be gathered from the place previously cited, and I Sent., d. xxxvii, q. iv, a. 3, and is the mind of Aristotle and the Commentator, VI Physics, ¹¹ is because every instantaneous change is the term of some motion. For everything that has been changed was previously being changed: and everything that has been generated was previously being generated, as is clear in the same place, comment 59. Therefore it cannot be that something in the last instant of some time has been changed, and yet in the whole preceding time rested.

3. It must be observed, however, that it is not the same to say that something in a whole time is under one form, but in the last instant of that time is under another form; and that something rests in a whole time under one form, but in the last instant has been changed to another form. For something can be under one form and yet under it not rest, but be changed: as is clear in that which is moved toward generation and in the last instant has been generated; for that remains for some whole time under the preceding form, yet it does not rest under it, but through alteration is in being corrupted, and continuously, while it is altered, is disposed in another and another way under that form, while it continuously approaches more to the corruption of it and the generation of the other.

VI. The proposition of St. Thomas being understood thus, however, it is manifest that the arguments of Scotus in the Second Book of the Sentences, d. 11, q. 11 ¹² are of no weight. For he argues first, because it would follow that in the last instant of the utterance of the words of Consecration, the form of bread would be there: because it was present for the whole time of the utterance.

Secondly because, since for some whole time the air rested in dark being, in the last instant of it it would be dark: and so illumination would not occur in an instant.

If however it is said, he says, that illumination is the term of local motion, to the contrary: — Let it be posited that the sun is newly created, and the medium preexisting: it is established that illumination will not be the term of local motion. — Now also that illumination is not per se the term of local motion, but some "where" acquired for the sun itself. — Nor can it be avoided through this that the air rested under dark being up to this instant.

2. To the first it is said first, that it is not against the sense of the proposition, which is understood according to the course of nature and concerning natural possibility. Here however the argument is about that which takes place miraculously and supernaturally.

It is said secondly that, although for the whole time of the utterance of the words the form of bread is present, it does not however rest: because through the succession of the words, which is a certain motion, the bread becomes more proximate to ceasing through conversion into the body of Christ; and by reason of this motion of the utterance of the words, whose term is the conversion into the body of Christ, becoming precedes having been made, just as in generation being generated precedes having been generated, by reason of the preceding alteration, whose term it is; as is clear in IV Sent., d. xi, ¹³ a. 3, q. 2, ad 3.

3. To the second it is said that the air does not rest for the whole time preceding illumination, since according to the course of nature illumination is the term of local motion. For according as the sun approaches more to the air through local motion, the air itself is more proximate to the reception of light. Whence according to the motion of the sun to the air, the air is said to approach to light and to recede from dark being successively, not through the loss of part after part, but through a greater and lesser approach to the light. For just as matter through alteration is disposed to the reception of the substantial form and to the casting off of the form that it has, on account of which it is said to be moved to form, although it receives it according to its whole self only in the last instant; so through the local motion of the sun, on account of which the air becomes more proximate to the sun itself, the air is disposed to the reception of light, which is in an instant, and on account of this successive approach it is said to be moved to light.

4. When however it is urged first concerning a newly created sun, it is said that it is not against the proposition: because we are not speaking of that which God can do through creation, but of that which is suitable to the natural course. — It can secondly be said that that creation of the luminous body supplies the place of local motion.

When it is objected secondly, because illumination is not per se the term of local motion: — this is denied of a new illumination. For although illumination simply is not per se primarily the term, or the intrinsic term, of this local motion, nonetheless a new illumination is per se a secondary and extrinsic term.

When it is objected thirdly that, this notwithstanding, the air rested under dark being up to the last instant: it is clear from what precedes that this is false. For although it was under dark being up to the last instant, it did not however rest under such being: because, although it was not the subject of any motion to light, nonetheless in the sun there was motion ordered to its illumination and to the expulsion of darkness.

VII. Sixth. That having been granted, it would follow that heaven, receding from the west against nature, would return to the east. This is impossible: since in heavenly motion there is nothing violent and against nature. Therefore etc. — The consequence is proved. Because the motion of heaven toward the west is natural. But in motion which is from nature as from an active principle, if approach to something is natural, recession from it is unnatural: as is clear in a heavy thing.

Observe that St. Thomas did not say absolutely, In motion which is from nature, if approach is natural, recession is unnatural, but added, as from an active principle: because namely, if motion is natural only on account of a passive principle, this is not necessary; for just as approach is natural, so also recession can be natural, as is clear in the motion of matter to form; for just as it naturally approaches to form, so it naturally recedes from it.

VIII. As to the second, ¹⁴ St. Thomas intends to remove certain doubts arising from the preceding.

The first is this. ¹⁵ Since it has been said that the motion of heaven is not solely from nature, but from an intellectual substance, it seems to follow that the motion of heaven is not natural.

To this he answers that that does not follow. For although it is not natural by reason of an active principle, but voluntary, it is nonetheless natural by reason of a passive principle, inasmuch as heaven has a natural aptitude for such motion: just as also the generation of simple bodies is natural by reason of matter, in which is a natural appetite for natural form, not however by reason of an active principle, since that is outside, but nature is a principle of motion of that in which it is.

The proposition, moreover, is made clear. Because each thing undergoes and is moved according as it is in potency, but acts and moves according as it is in act. But a heavenly body, considered according to its substance, is found as being in potency indifferently to any "where", just as prime matter to every form: which is not found in a heavy and light body, which, considered in its own nature, is not indifferent to every place, but from the ratio of its form a place is determined for it. From this it is deduced that the motion of heavy and light things, when they are moved by us through intellect, is violent: because in them there is a natural aptitude for the contrary motion to that by which they are moved by us; although the motion of an animal body by the soul is not violent, inasmuch as it is animate. But the motion of heavenly bodies is not violent: because heavenly bodies do not have an aptitude for the contrary motion, but for that by which they are moved by an intelligent substance.

2. It must be noted first that, since nature is divided by matter and form; and nature is a principle of motion of that in which it is: for motion to be natural, it suffices that it proceed according to the inclination of either of these, namely of matter or of form. And therefore it is not unfitting for motion to be natural from the sole aptitude of matter, and of nature by mode of potency, for such motion, although the active principle of motion is extrinsic.

It must be noted secondly, when it is said that the motion of heavy and light things by us is violent because they have a natural aptitude for the contrary motion, that this is understood of an aptitude determined to such motion with repugnance to the opposite motion: not however of an aptitude indifferent to both motions, as in heaven there is an aptitude indifferent to all "where"s.

It must be noted thirdly, when St. Thomas says that heaven according to its nature is indifferently disposed to any "where", that he therefore added according to its nature, because, although from the intention of the moving substance heaven can be determined to some "where", nonetheless, the nature of heaven considered in itself, it is not determined to some "where".

It must be noted fourthly, that the soul, as is said in the First Part, q. lxii, a. 2, ad 2, as far as it is of itself, is naturally suited to move in any direction. Therefore it is necessary that the motion of an animal, which is from the soul, is natural, just as also in heavy and light things the motion which is from the form of them is natural: for that is natural motion which is from an intrinsic principle. On this account it is well said here that the motion of an animal body, inasmuch as it is animate, is not violent to it, although it is violent to it inasmuch as it is a certain heavy thing. For the body of an animal, although it is informed by the soul alone and not by another form, nonetheless inasmuch as it is informed by the soul as it is soul, is apt to be moved in any direction: inasmuch however as it is informed by the soul as it is the form of the body, which heaviness follows, it is apt to be moved only downward. And therefore it is said in VIII Physics ¹⁶ that the animal indeed moves its whole self naturally: but the body, according as it is a body, happens to be moved by nature and outside nature.

IX. Concerning what has been said, a twofold doubt occurs. The first is this. For the Commentator, VIII Phys., comm. 27, ¹⁷ holds that the motion of a heavenly body is simply natural, both on the part of the soul and on the part of the body. Therefore what is said here is not true, namely that it is natural only by reason of a passive principle.

The second doubt is this. If the soul is naturally apt to move in every direction, the animal's body, inasmuch as it is ensouled, is indifferent to every motion and to every place. And yet its motion is natural on the part of the form. Therefore, from the fact that the heaven is indifferent to every where, it does not follow, as St. Thomas deduced, that its motion is natural on the part of the passive principle alone; rather, it can be natural also on the part of the active principle.

2. To the first of these it is said, first, that the Commentator seems to have spoken variously on this matter. For in the cited passage it seems that the motion of the heaven is natural both on the part of the active principle and on the part of the passive principle; but in I De Caelo, comm. 5, and II De Caelo, comm. 3, he seems to maintain that it is natural only on the part of the passive principle.

For the reconciliation of his statements, however, and also with St. Thomas, it could be said, setting aside the response of others, that motion can be called natural on the part of the active principle in two ways. In one way, because the active principle of the motion is intrinsic to it as its form. And in this way the motion of the heaven is not natural, neither according to St. Thomas nor according to the Commentator, because the active principle of its motion is a form abstract according to esse. In another way, because the active principle of the motion is naturally apt to move such a body without resistance, and is appropriated to that body for moving. And in this way the Commentator understands the motion of the heaven itself to be natural from an active principle, for he takes the heaven to be the composite of an intelligence and a celestial body. Hence in I De Caelo, in the cited commentary, he says that abstract forms, according as they are abstract forms, are naturally apt so that that which is moved by them is a body neither heavy nor light, just as they are naturally apt so that what is moved by them is round, and just as the form of fire is naturally apt to have its proper matter. And in VIII Physic., in the adduced passage, he maintains that the motion of the heaven is through a principle in it in such a way that in its body there is no principle contrary to the motion of the soul. Moreover, by the name of heaven he there also takes the composite of the celestial body and the moving intelligence, which can in some way be called its soul, inasmuch as it is appropriated to it for moving.

It is clear, therefore, that there is no contradiction either among the statements of the Commentator, or between the Commentator and St. Thomas, since St. Thomas speaks of natural motion from an active principle in the first way, whereas the Commentator speaks of the natural in the second way.

3. To the second it is answered that motion can be called natural on the part of the form in two ways. In one way, because it is from an intrinsic form not acting through apprehension, but moving merely naturally. In another way, because it is from an intrinsic form not acting by violence, but which is naturally apt so to move, and the movable is naturally apt to be so moved by it as it is subject to that form. Therefore, indifference to diverse wheres shows that the motion is not natural on the part of the form in the first way, that is, that it is not according to the inclination of a form moving without apprehension, because such a form inclines determinately to one thing. And in this way St. Thomas argues from the indifference of the heaven to all wheres that its motion is not natural on the part of its form, since that is a merely natural form. Such indifference, however, does not show that the motion is not natural in the second way, because a form acting through apprehension can move its movable to diverse things according to the diversity of apprehensions. And thus it is not unfitting for a movable to be indifferent to diverse wheres inasmuch as it is naturally apt to be moved by such a form; and for its motion to be natural inasmuch as it is moved by an intrinsic form thus naturally apt to move; and for it to be naturally apt to be moved by it in this way inasmuch as it is subject to such a form, although from elsewhere it is inclined only to the opposite motion. Hence, to the objection, it is denied that the motion of an animal, as it is an animal, is natural on the part of the form in the way in which St. Thomas in this passage speaks of natural motion on the part of the form when he speaks of the motion of the heaven.

X. The second doubt which St. Thomas removes ¹⁸ is this. For someone could argue that the motion of the heaven is not voluntary, because it is one and uniform; but the will relates to many things and is not determined to one.

But he answers that the will is determined to one through its wisdom, by which it is directed infallibly to one end, just as nature is determined to one through its power. Therefore, that the motion of the heaven is voluntary is not repugnant to its unity and conformity.

For the evidence of this response, it must be considered that, since the will follows intellective cognition and is directed by it as by its rule; although, the nature of the will being considered absolutely, the will is an indifferent cause and not determined to one; yet, inasmuch as it follows the judgment of the intellect judging that something is to be willed and done, it has a determination to that thing, so that on account of it it acts determinately; and it can move to some end uniformly and infallibly when both the cognition by which it is directed is infallible and certain, and the will itself cannot be impeded in its effect. And thus, since the will of the substance moving the heaven cannot be impeded, and is directed by infallible and certain wisdom to one end, that intellectual substance uniformly and infallibly moves the heaven to the end which it intends in moving, and does not relate to the motion of the heaven as an indeterminate cause, but as one limited to one.

XI. The third doubt which he excludes ¹⁹ is: If the motion of the heaven is natural, it seems that in celestial motion there could be something contrary to nature, just as in the motion of heavy and light things.

He answers from the premises that it is not similar. For neither approach to some where in the motion of the heaven, nor departure from it, is contrary to nature, as in heavy and light things. First, because in heavy and light things the intention of nature is determined to one place, approach to which is natural and departure from which is contrary to nature. Second, because the motion by which there is approach to the middle (understand this of the middle of the world) and the motion by which there is departure from it are contrary. But the intention of nature in the motion of the heaven, according to which nature, namely, their motion is called natural, is not toward some determinate where. And the motion by which it departs circularly from some point is not contrary to the motion by which it approaches it, but is one and continuous. For just as both the approach and departure of heavy and light things with respect to a middle place between the extremes is natural, and they are not contrary motions, but one continuous motion, because the whole, namely, such approach and departure, stands under one intention of nature; so also in the motion of the heaven; for any where in the motion of the heaven is like a middle in rectilinear motion, not like an extreme.

Note that the motion of a heavy thing by which there is departure from the middle of the world tends to the place above which is contrary to it; and because the motion upward and the motion downward of a heavy body are contrary, as tending to contrary places, therefore it is rightly said here that the motions of which by one nature approaches the middle and by the other departs, are contrary. But the motion of the heaven by which there is approach to some point is not contrary to that by which there is departure from it, because the motion by which there is departure from some point is not to a where contrary to that to which there is approach, since in circular motion there is no contrariety according to some points designated on the circle insofar as they are points of the circle itself; although in some way there can be opposition according to them insofar as they are extremes of the diameter, according to which the greatest distance in a circle is measured, as St. Thomas says in I De Caelo, in the exposition of text 87 ²⁰.

XII. The last doubt ²¹ is this. For because it was said that the motion of the heaven is from an intellectual substance, someone could ask whether that substance is conjoined to the celestial body so as to be its soul, or is separate. And whether it is the first substance that immediately moves the heaven, or a created substance through which as intermediary it moves; or the first substance moves the first, and other substances move others.

St. Thomas answers that it matters nothing whichever of these is said, provided it is maintained that celestial motion is from an intellectual substance.

It must be noted that St. Thomas wishes to obtain nothing other from this reasoning of his than that the motion of the heaven is not merely natural, but partly natural and partly voluntary. Now this is maintained whether it is posited that the intellectual substance moving is the form of the heaven, or it is posited that it is separate. For since it is not of the nature of a mover that it be intrinsic to the moved, a voluntary mover can be both intrinsic and extrinsic: for the progressive motion of a man, which is from a conjoined soul, is voluntary; and the motion of a wheel by a separate man is voluntary. On this account it is rightly said here that it matters nothing to the purpose whichever of those is said.