Commentaria in Summam contra Gentiles, Liber II

After St. Thomas has shown that there are some intellectual substances united to bodies, he wishes further to show that there are also some intellectual substances that are not united to bodies ¹. Concerning this he does two things principally: first, he shows that there exist some such separate substances; second, he determines their multitude, in the following chapter.

I. As to the first, he argues first as follows. When bodies are corrupted, as was shown above, the substance of the intellect, being as it were everlasting, remains. Therefore there is some intellectual substance subsisting without a body.

The consequence is proved. If that intellectual substance which remains is one for all, the point is established. But if several souls remain, then it belongs to some intellectual substances, which are souls, to subsist without a body. Therefore there are also some intellectual substances, prior by nature to souls, to which it belongs of themselves to subsist without bodies. The second consequence is proved: because for everything that is per accidens, that which is per se is prior; but it belongs to souls per accidens to be separate from bodies, since by nature they are forms of bodies.

It must be noted that, since the intellectual soul does not possess the complete species within itself but is a part of the species, it belongs to it per se to be in a body, in which it has the complement of its species; but it remains separated from the body per accidens, insofar as it happens to it that the body to which it was joined is corrupted. For if the body could be preserved immune from corruption, the soul would never be separated from the body. And therefore Saint Thomas rightly says that it belongs to souls per accidens to be separated from the body.

Second. It belongs to an intellectual substance, according to its genus, that it be subsistent through itself, since it acts through itself. Therefore it is not of the essence of its genus that it be united to a body, although this is of the essence of the soul. Therefore, etc. — The first inference is evident, because it is not of the essence of a thing subsistent through itself that it be united to another. — But the second is proved as follows: although what is of the essence of the genus must be of the essence of the species, nevertheless not everything that is of the essence of the species and not of the essence of the genus must belong necessarily to all the species of the genus.

Note that this proof of the last consequence, although it seems to lead only to the conclusion that it is not necessary for an intellectual substance to be united to a body, and consequently that it is possible for there to be one not united to a body, nevertheless from that very proof it is also concluded that there is such a substance not united to a body. For just as a specific difference does not necessarily belong to all the species of a genus, so in fact the genus is found in some species without such a difference: since the genus is divided by opposite differences, just as it is found with one difference in the nature of things, so too must it be found with the other, considering the nature of things. Hence, if the genus of intellectual substance is found with this difference, namely being united to a body, it must also be found with the opposite difference, namely being not united to a body. And thus there must be some intellectual substance not united to a body.

Third. The intellective soul is the lowest in the genus of intellectual substances. Therefore there are other intellectual substances naturally superior to it, not united to bodies. — The antecedent is proved. Because the intellective soul is united to the highest in the genus of bodies: but a superior nature, in its lowest member, touches an inferior nature in its highest. — How the human body is nobler than a celestial body, and consequently the highest of bodies, was shown above ².

Fourth. There are some complete forms subsisting per se in species. Therefore, etc. — The antecedent is proved. Because forms that are in matter are imperfect acts. But if there is something imperfect in any genus, there is found prior to it, in the order of nature, something perfect in that genus: for the perfect is by nature prior to the imperfect. — The consequence is also proved. Because every form subsisting per se without matter is an intellectual substance.

Concerning this proposition, If there is something imperfect in a genus, there is found before it, according to the order of nature, something perfect in that genus, it must be noted that the truth of this proposition is not founded on the fact that act is prior to potency; nor on the fact that among the differentiae of one genus one has the character of the perfect and another that of the imperfect; but on the fact that the perfect is prior by nature to the imperfect, as is touched upon here. For, if what is posterior in some order exists in nature, it is fitting that what is prior by nature in that order also exist: since the imperfect is for the sake of the perfect, and the perfect is intended before the imperfect. Otherwise that order, and that genus, would not have the complement of its perfection in nature; yet the perfection of the universe requires that each order have the complement of its perfection.

III. Fifth ³. There can be in the genus of substance certain things entirely without body: because substance is prior to the other genera in time, in reason, and in knowledge; and consequently it can exist without quantity, and even without body, which does not exist without quantity. Therefore, etc.

The consequence is proved. First, because all possible natures are found in the order of things. Then, because otherwise the universe would be imperfect. — Then, because in eternal things esse and possibility do not differ.

IV. In the proof of the antecedent, a doubt arises that must not be concealed. For if from the fact that substance, which is a category, is prior in time, in reason, and in knowledge to all the other genera, it follows that it can exist without quantity and body, then by the same reasoning it would follow that it could exist without any other genus. But this is against the doctrine of St. Thomas, who holds, Prima, q. XLIV, a. 1, ad 1; de Pot., q. VII, a. 9, ad 5; and Quodlibet VII, a. 10 ⁴, ad 4, that a creature cannot be without the relation of dependence on God, which is an accident. Now it is evident that every substance that is in a genus is created substance. Therefore no substance in a genus can be separated from every accident. Therefore by that assumption the antecedent is not effectively proved, but the consequence is false, namely: Substance is prior in time, in reason, and in knowledge to all the other genera; therefore it can exist without quantity.

2. There is also doubt concerning the assumption taken for proving the consequence⁵. For if all possible natures are found within the order of things, it follows that God can produce no species other than those that have been produced: for all the natures producible by Him, according to that proof, are in act. But this is contrary to the determination of Saint Thomas, who holds in the Prima, q. XXV, a. 6; De Veritate, q. XX, a. 4; I Sent., d. XLIV, q. 1, a. 3; and above in this Second Part, chap. XXVI and XXVII, that, given any species whatsoever, God can produce nobler ones to infinity. Therefore, etc.

3. Finally, concerning the second proof of that assumption, a doubt arises ⁶. For since it is assumed that in eternal things esse and posse do not differ, either by "eternal" are understood those things which have not had the beginning of their duration, or those things which are incorruptible in their nature. If it is taken in the first way, what is proposed does not follow, but there is a begging of the question. For one must subsume: But subsistent substances existing outside bodies are eternal, that is, they have not had the beginning of their duration. This is not only false, but includes what is to be proved, namely, that such substances exist. — But if it is taken in the second way, it is false that in them esse and posse do not differ. For such incorruptible things, according to the faith, were previously able to be before they were brought into act. And thus it does not seem that what is proposed is confirmed by that proposition.

V. To make the first doubt evident, it must be considered that it is quite clear what Aristotle intends in Metaphysics VII ⁷ when he says of substance that it is prior to accident in reason and in knowledge. For since the reason of an accident depends on substance, because substance is posited in its reason, whereas the reason of substance does not depend on the reason of the accident, therefore substance is prior to accident in reason. Similarly, since knowledge of substance does not depend on knowledge of the accident (I speak of intellectual knowledge of each), while knowledge of the accident, insofar as it is an accident, does depend on knowledge of substance, since the reason of substance must be posited in the reason of the accident, therefore substance is said to be prior to accident in knowledge. Or also because it is prior in perfection of knowledge: for, as the Philosopher says there, we think we know individual things most fully when we know what man is or fire, rather than when we know what sort, how much, or where. — But it is doubtful what is meant by the statement that it is prior in time. For this different people interpret in different ways.

For Averroes understands that, in the same place ⁸, to be said only of the accidents of generable and corruptible things. For either they are accidents following upon the composite: and then it is certain that the composite substance precedes them in time. Or they are accidents accompanying the composite inseparably: and then, although the composite itself does not precede such accidents in time, yet the matter from which the composite is made precedes them in time, just as it also precedes the composite. And thus it is universally true that substance is prior in time to the accidents of generable and corruptible things: speaking of accidents in act, not of accidents in potency, of which sort are, according to him, the indeterminate dimensions.

Scotus, however, in II Sent., d. 1, q. 5 ⁹, interprets that statement about substance in comparison to all accidents. For he holds that there is no contradiction on the part of substance in its being able to precede every accident in duration.

St. Thomas, however, in Metaphysics VII ¹⁰, explains that some substance is found without accident, but no accident is found without substance: and thus not whenever there is a substance is there an accident, but the other way around.

2. Some expound this interpretation of St. Thomas by saying that he understands it of the first substance, which is God; and that under the name of time he understands every duration. For the sense is that substance is prior to the duration of accidents, insofar as the measure of substance, at least of God, which is eternity, is prior to the duration of accidents, which is time.

This interpretation seems to have been devised as an escape. For, since time is posited to be eternal, according to Aristotle ¹¹, it is difficult to preserve the claim that first substance, which is God, is prior in time to accident, taking time properly. By this route, however, escape is easy: for it is not unfitting—indeed it is most true—that God be prior to every duration of eternal time, insofar as He is in eternity, which is a duration prior and more perfect by nature than time, since it exists all at once, as Boethius says in Book V of the Consolation ¹². But this does not seem to be Aristotle's mind: for, since above, in the fifth book ¹³, he declared what it is to be prior in time, it is not fitting that here he should say something is prior in time in a sense other than what the words signify according to the meaning given by him, unless he himself expounds a new signification. — Moreover, we do not use this way of speaking when comparing something with respect to duration—not whenever "when this is, that is," which is how St. Thomas uses it—unless the comparison is made in time on the part of both: since "whenever" is an adverb of time.

3. And therefore, with due deference always to a better judgment, I would say that the mind of St. Thomas in this place is that, following the position of Aristotle, who posits the world as eternal, substance is prior to accident in time—not in act, but in potency, which signifies non-repugnance—just as Scotus also explains ¹⁴. For although, according to Aristotle, there was never a time in which there was substance and no accident, yet since God is without all accident, as having no dependence upon accident, it follows that there is no repugnance, so far as the reasons of the terms are concerned, for it—and consequently for some substance—to be at some time at which there is no accident; and thus to precede every accident in duration and in imaginary time. Hence, when St. Thomas says, in expounding Aristotle's mind, that not whenever there is substance is there accident, but conversely, it must necessarily be understood thus: namely, that it is not necessary that whenever there is substance there be an accident, considering the proper reasons of substance and accident; although accidentally, whenever one exists the other does too, from the fact that it happens to substance, as such, that the world was produced from eternity.

It can also be expounded of created substance absolutely, insofar as it participates in the common nature of substance. For it is not repugnant that there be some created substance without any accident, considered absolutely under the nature of substance; and thus that it be prior in time to accident.

4. But against the first exposition of St. Thomas ¹⁵ it seems that God is not placed in the genus of predicamental substance. Yet Aristotle seems to be speaking of predicamental substance when he says that it is prior in time to accident.

This can be answered in two ways. First, the Philosopher does not take the category of substance properly speaking, as it is one genus; rather, under the name of substance is comprehended every substance, namely both infinite and finite. And thus it is not denied that God is in the category of substance.

Second, that although God is not in the category of substance as something contained and comprehended under it, He is nevertheless in it as the principle of the whole category.

From these things it is evident that Scotus, in this exposition, does not disagree with Saint Thomas.

5. But if it is urged that this is a priority of nature, since what is prior can be without the posterior, but not conversely, whereas Aristotle here speaks of priority of time — the answer is that there is no inconsistency in something's being prior in time and also prior in nature. For Aristotle himself, at the end of the chapter on Prior and Posterior in Metaphysics V¹⁶, says that all the modes of prior and posterior are reduced to priority and posteriority according to nature, insofar as that is called prior which can be without another, but not conversely. Hence also, where in some Greek codices, at the passage cited from Metaphysics VII¹⁷, "and by nature" is added, this must be understood of a priority of nature according to that mode whereby the more perfect are prior to the less perfect: not according to that mode whereby something is said to be prior in nature from which the consequence of subsisting does not hold for another. For this latter priority is meant when he says that substance is prior in time: since such a thing is also, without repugnance, prior in time in the manner stated¹⁸; which is clear because, explaining how he understands substance to be prior in time, he says that none of the other categories is separable, but substance is separable; for the separability of one from another, and not conversely, is the ground of one mode of priority according to nature.

But if it be asked why he did not say that it is prior in nature, in place of what he said, that it is prior in time: — the answer is that he did so in order to distinguish that mode of priority according to nature by which something can be separated from another with respect to being, which pertains in some way to temporal priority, from that mode by which that which is more perfect is said to be prior in nature. Which latter mode, indeed, he added afterward, as some Greek codices have, saying "and it is prior in nature": for we frequently signify that mode by the common term itself, namely, prior in nature.

VI. To the doubt¹⁹ therefore, following the first exposition of Saint Thomas²⁰, it is said that the objection is not to the point: because substance is said to be prior in time by reason of that substance which is God, in which there is no accident; but not by reason of any created substance.

2. Following another exposition²¹, it is said first that substance, insofar as it follows from the notion of substance and accident, can indeed be without every accident, since it does not depend on accident with respect to its esse. Yet from something else it can come about that no created substance can be without some definite and determinate accident: as, for instance, that man cannot be without risibility, because risibility follows upon something that belongs to the notion of man insofar as he is man. Hence, if there is an accident that does not follow upon the proper notion of a given substance, that substance can be without it.

It is said second, that a relation of dependence on God accompanies predicamental substance insofar as it is not its own esse, but is a being by participation, and consequently is a being caused by another. And on account of this, although predicamental substance, considered only under the aspect of substance in it, can exist without such a relation, and thus is prior in time in the manner explained, because caused esse does not follow upon the aspect of a subsistent simply, since there is found some subsistent being that is not caused, namely God; nevertheless, considered under its proper aspect, inasmuch as it is a subsistent being having participated esse, no predicamental substance can exist without such a relation.

It is said third, that the case is not the same for quantity and for this relation. For quantity does not follow upon predicamental substance either insofar as it is a subsisting being, or insofar as it is such a subsisting being as has participated esse: for it does not appear what necessary dependence it has on the ratio of substance, whether taken absolutely or limited to the predicament and genus. Hence the argument of St. Thomas concludes excellently concerning quantity, if it be well understood, and if there be supplied what is passed over as manifest. But it would not conclude concerning the relation in question. For the argument runs: Predicamental substance, insofar as a subsisting being, is prior to quantity and the other genera in time, in reason, and in knowledge. And quantity has no ratio of natural concomitance with it taken according to its proper ratio. Therefore predicamental substance can exist without quantity. But one could not thus argue concerning the relation of dependence on God: because something false would be assumed, namely that relation has no natural concomitance with predicamental substance. — From these things it is clear that the consequence of St. Thomas must not be taken so nakedly as is supposed in the objection, namely: Predicamental substance is prior in time, reason, and knowledge to the other genera; therefore it can exist without quantity: but one must supply in the antecedent: and quantity has no natural concomitance with it considered according to its proper ratio. And then it plainly appears that the objection brought forward does not break the course of the reasoning.

In a similar way one must interpret the reasoning of St. Thomas in the Questions on Spiritual Creatures, article 5, which seems to be the same as this one. For he assumes this proposition: If there are two things of which one does not depend on the other according to its reason, it is possible for that thing to be found without the other. For something must be added to the antecedent: and the other has no natural concomitance with it. — Hence he himself, in the First Part, question 44, article 1²², arguing that certain beings can exist without a relation of dependence on God, on the ground that nothing prevents a thing from being found without that which is not of its reason; yet the relation of the caused to its cause does not seem to be of the reason of beings: he replies that, although the relation to the cause does not enter into the definition of the being that is caused, it nevertheless follows from those things that are of its reason. From which reply he gives us to understand that the major premise must be understood as we have expounded it.

VII. To the second doubt²³ it is answered that Saint Thomas is speaking of what is possible with respect to the essential perfection of this universe. Hence he does not say simply that all possible natures are found, but that they are found in the order of things, that is, in the universe, whose unity is the unity of order. Now it is certain that in the essential order of this universe there are only those things that pertain to the perfection of the universe itself. But not all natures producible by God pertain to the essential order and perfection of the universe; rather, all the universal modes of being known to us do. Otherwise it would not be a universe, for it would not include all the modes of being. Now the general modes of being of created things subsisting per se are three: namely, material corruptible being; material incorruptible being; and immaterial and incorruptible being. Nor does it appear that any other mode of being of creatures is possible. Therefore, in order that the universe be perfect, since this mode of being, which is immaterial and incorruptible being, and consequently intellectual being, is possible, this mode of being too is required for the perfection of the universe.

VIII. To the third doubt²⁴ it is answered that that proposition of Aristotle, Physics III, text 32, holds true in incorruptible things, whether they are supposed never to have had a beginning of their duration, or to have begun through creation. For as the Commentator explains there; in De Caelo II, commentaries 33 and 34; and St. Thomas, De Potentia, q. iii, a. 14, ad 5, this is understood of passive potency, by which something is said to be able to receive what it does not have: for where such a potency exists which is receptive of another form than the one it has, that thing is corruptible, because passive potency separated from act is the principle of corruption. Hence the meaning is that in perpetual things, or in incorruptible ones, there is no passive potency separated from substantial act, nor even from any other act having the character of a permanent form when present in the subject and expelling another preexisting form. From which it follows that, just as the perpetual cannot cease to be through corruption, so it cannot begin to be through generation. Because by the same reason that no potency is in it which regards another act, by the same reason no potency precedes it which, existing under another form, could receive the form of this thing, from which potency it would be said to have been made: for such a potency together with the form it has would coexist with the privation of the other form, and consequently would be a principle of corruption.

But although, in this sense, it may have truth in all things, and by this means it is not ruled out that they may have a perpetual beginning of their duration, as first existing in potency in the Creator and afterwards brought into act through creation: nevertheless St. Thomas takes it in a broader sense, namely that in which it was taken by certain philosophers against whom he argues principally; namely, that in these things the possible is the same as the necessary, in which way the Commentator says, Physics III, comment. 32, that when something has been possible of being among eternal natures, it will be necessary, not contingent. For then it follows that if intellectual substances subsisting apart from bodies can be, they are in fact in act: because "possible" is not said of such incorruptible things in the manner of the contingent, as if, while they can be, they can also not be.

But if it is said that from this proposition not only will it be concluded that they are, but also that they have been from eternity, because they were able to be from eternity: — the reply is that this indeed could be concluded; and, if it were concluded, Saint Thomas would have his position all the more against those natural philosophers who, not distinguishing between sense and intellect, said that every substance is corporeal. He did not wish, however, to conclude anything except what pertained to his purpose.

From these things the solution to the argument on the opposite side is evident. For although, according to the faith, created things were possible before they existed in act, this is not true according to the philosophers against whom Saint Thomas argues. Hence he takes that proposition in the sense in which it is conceded by them, not in the sense that is true absolutely and simply.

IX. Sixth²⁵. A substance composed of body and intellectual substance is found to exist. And a body is found without intellectual substance. Therefore, all the more are intellectual substances found not united to bodies. — The consequence is proved. Because if from two things some composite is found; and the lesser of them is found per se; then that which is greater and more perfect, and less in need of the other, is found per se.

Concerning this last proposition, note that it is taken from Book VIII of the Physics, text 37²⁶, and it holds true of those things that are joined wholly by accident. For those things that are joined per se according to logical perspicacity are inseparable: so that one without the other cannot be found, at least naturally; or at least that which necessarily depends on the other, even if the other does not depend on it necessarily. And, as Saint Thomas says in the same place, of those things that are joined wholly by accident, one can be found without the other if the other is found without it: this is probable; thus, because sweetness and whiteness are joined in sugar, and white is found without sweet, as in snow, likewise sweet is found without white, as in cassia. But that either of them can be found without the other with logical possibility, which signifies the non-repugnance of the terms, is necessary: for things joined by accident can fail to be joined. — This proposition was also discussed in the first book²⁷.

But it must be noted that what belongs per se to the inferior can belong per accidens to the superior: just as certain accidents of an individual, inseparable from it, are related per se to the individual, as consequences following upon its substantial principles, which, when compared to the species, are related per accidens, since they do not follow upon the principles of the species, as perhaps blackness is related to the raven; and therefore it is not repugnant for the species to be found without that accident, although it is repugnant for the individual. Similarly, then, in the case at hand: to be the form of a body belongs per se to this intellectual substance which is the intellective soul; but in relation to intellectual substance considered absolutely and in general, it is related per accidens; for it does not belong to the ratio of intellectual substance, nor does it follow from its ratio, that it be the form of a body, since understanding is not exercised through a bodily organ. Therefore, that some intellectual substance can be found which is not the form of a body but exists without a body is necessary. That it is in fact found without a body, given that a body is found without it, is probable and consonant with the nature of the thing.

X. Seventh. To understand only through reception from sensible things, and to understand only those things that are not intelligible in themselves but become intelligible through the intellect, is an imperfect mode of understanding. Therefore there must be another, perfect mode of understanding, by which are understood those things that are intelligible in themselves. Therefore, before human souls—which understand by receiving from phantasms—there must be other intellectual substances that understand the things which are intelligible in themselves, not receiving from sensible things, and thereby wholly separate from bodies by nature. — The first inference is proved: because before every imperfect thing there must be something perfect in that genus. — The second is also proved: because a thing's substance must be proportionate to its operation. Now understanding, since it is not exercised through an organ, has no need of a body except insofar as intelligibles are taken from sensible things.

It must be noted that by what is said here, Saint Thomas does not intend to exclude entirely from the knowledge of the intellectual soul those things that are intelligible in themselves, nor from the knowledge of the intelligences those things that are not intelligible in themselves; rather, he intends that the intellectual soul does not understand perfectly and quidditatively except material things, while immaterial things, even if it knows them in some way, it nevertheless knows only imperfectly, and only from sensible things. The intelligences, however, do indeed know material things perfectly and quidditatively, but not through reception from sensible things. And the object proportioned to them is rather an immaterial thing than a material one; on the contrary, material things are the object proportioned and connatural to the intellectual soul.

It must also be noted, when it is said that esse is an imperfect mode of understanding, in that it takes intelligibles from sensibles and understands nothing except what is not intelligible in itself, that this is not to be understood as though material things are not perfectly understood—for that would be false—but because understanding, considered absolutely, is imperfect if it extends only to material things and exists only through reception from the senses; for it does not possess every perfection that by its nature is fitted to belong to intellection. But an understanding that extends both to what is per se intelligible and to what is not per se intelligible, and has no dependence on the senses, is perfect understanding universally and absolutely.

XI. Eighth: and this is Aristotle's argument, Metaphysics XII, ²⁸ text 43. There are many movers of the heavenly bodies which are moved neither per se nor per accidens. Therefore there are many movers that are neither bodies nor united to bodies. Therefore etc.

The last consequence is evident, because the celestial motions are from some intellect, as was proved above. The second is also shown, because a body does not move unless it be moved; but an incorporeal mover united to a body is moved per accidens with respect to the motion of the body, as is evident in the case of the soul. Now the antecedent is proved: for there are many celestial motions that are continuous and regular and, so far as they themselves are concerned, unfailing. But there must be several such motions from several movers who are moved neither per se nor per accidens—that is, movers which move by way of an end, as will be said in the following chapter.

XII. Concerning this argument a difficulty arises. For, as was shown in the First Book, chapter XIII²⁹, according to the mind of St. Thomas in Prima, q. LI, a. 3, ad 3; and II Sent., d. VIII, a. 4, ad quartum quaesitum, if the substances moving the heavenly bodies were united to them as movers are to things moved, they would not be moved per accidens, because the heavenly bodies do not pass from place to place. But this same reasoning holds even if they were united to them as forms: for neither would they then pass from place to place. Therefore it cannot be concluded that movers of this kind are not united to bodies on the ground that they would not be moved per accidens. For it could be said that, even granted that they were united to bodies, they would nevertheless not be moved per accidens. And so that proposition does not seem to be universally true: An incorporeal mover united to a body is moved per accidens.

It can be answered, according to the doctrine of St. Thomas, Qu. de Spiritualibus, a. 6, ad 9; and VIII Phys. ³⁰, that one must speak differently of the mover of the heavenly body if it is united to the heavenly body as mover only, and differently if it is united to it as form. For if it is united as mover only, there is no union between them according to esse, but only according to power, inasmuch as it applies its motive power to the body. Now it does not belong to a mover, insofar as it is a mover, to be moved per accidens by the motion of the body moved by it, except because the mover must be together with the thing moved; and therefore, when the moved body departs from one place, the mover must also depart from that place, otherwise it would not be together with the thing moved. But if the thing moved does not depart from the place in which it is, however much it is moved circularly in that place, the mover need not be moved: for it is always joined to the mobile in that place. And this is to be understood if the mover is united with its power to the whole mobile at once: for if it were united to only one determinate part of the orb, which is now in the east, now in the west, then, in order to be together with the thing moved, the mover itself would have to be moved per accidens by the motion of that part. — But if we posit an incorporeal mover united to the heavenly body by way of a form giving esse, the union there is not by contact of power alone, but according to esse, so that there is one and the same esse of the whole composite and of its parts. And therefore, according to the motion of the whole, the mover itself must also be moved, though per accidens: for it belongs to an essential part, as having the same esse as the whole, that at the motion per se of the whole, however it is moved, whether from place to place or circularly in the same place, it be moved per accidens. And therefore, just as the whole heaven is moved circularly per se, insofar as its parts change place really, while the whole itself changes place only according to reason; so the mover joined as a form giving esse is moved per accidens by that same motion.

It is therefore clear that what is said here about an incorporeal mover united to a body, and what was said in the First Book, are both true. For here Saint Thomas speaks of such a mover as united by way of a form giving esse, as is clear from the example of the soul; but there we spoke of it as united only by way of a mover.

XIII. Finally, the conclusion is confirmed by the authority of Dionysius, chapter 4 of On the Divine Names. — There is also excluded from it the error of the Sadducees, who denied that spirit exists; the error of the ancient Naturalists, who said that every substance is corporeal; and the error of Origen in the book Peri Archon; and of all others who say that all angels, both good and evil, have bodies naturally united to themselves.

One must attend, with respect to all the arguments adduced in this chapter, that Saint Thomas does not intend to prove the necessity of the esse of the separate substances as though God could not have refrained from producing them, speaking absolutely: for this would be heretical, since it would posit God as acting by a necessity of nature. Rather, he wishes to show the fittingness and probability of their esse, considering the nature of things. For this reason he often added in the arguments, according to the order of nature: namely, so as to show that he was proving what the order of nature requires, not what would be absolutely necessary to come about.