Commentaria in Summam contra Gentiles, Liber III

Because in response to what was said in chapter eighty-five someone could say that, although the heaven cannot by corporeal power be the cause of our choices, it can nevertheless be their cause by the power of a moving soul, St. Thomas wishes to exclude this evasion ¹. And he does two things: for first he rehearses the opinion of certain thinkers; secondly, he removes it ².

I. As to the first, he says that Avicenna posited that the motions of the celestial bodies are the cause of our choices, not by way of occasion only, but per se. For since celestial motion, according to him, is from a soul, and is the motion of a body, he said that just as, inasmuch as it is the motion of a body, it has the power of transmuting bodies, so inasmuch as it is from a soul, it has the power of impressing upon our souls. — To the same point also, says St. Thomas, the opinion of Albumasar in the first book of his Introductorium comes down.

II. As to the second, he argues against the aforesaid position. First thus ³. The action of a celestial body in no way extends to the change of the intellect and the will, except perhaps per accidens, as was shown above ⁴. Therefore the soul of the celestial body, if it is ensouled, cannot impress upon the intellect and the will by means of the motion of the celestial body. — The consequence is proved. Because, since every effect that proceeds from an efficient cause through some instrument must be proportioned to the instrument, just as to the agent, that cannot be brought about through some instrument to which the action of the instrument in no way extends.

III. To this reason someone would perhaps say that it begs the question. For this is what must be proved: that the action of a body in no way extends to the change of the intellect and the will. For it will be said that, although the action of a body, as it is a body absolutely, does not extend to the change of the intellect and the will, it nevertheless extends to it inasmuch as it is the instrument of a moving soul: just as it is also posited by St. Thomas himself in IV Sent., d. IV, q. I, a. 1 ⁵, that a sensible thing which is a sacrament, inasmuch as it is an instrument of God, causes in the soul a character, or a certain adornment, which is a species of quality, even though a body cannot by its own power act upon a spirit.

IV. But if this reason is carefully considered, it will be apparent that there is in it no begging of the question, but that it is efficacious and proceeds in the right order. For it is one thing for an instrument to be capable of some effect of which it would not be capable by the power of its own nature; and it is another thing for it to be capable of reaching some patient, by causing some form in it, which patient it could not reach by its own proper action. For there is no doubt that the first can belong to an instrument: for the natural heat of an animal can by the power of the soul, as its instrument, generate flesh, which it could not generate by its own power. But the second is entirely impossible. For an instrument cannot by the power of the principal agent introduce some effect into some patient which it cannot reach by its own proper action. For we see that heat, which is an instrument of the soul, by its own proper action, which is heating, reaches the body into which food is converted by the power of the soul. Likewise we see that a saw reaches by its own proper action, which is cutting, all that matter into which art introduces an artificial form through it, as through an instrument.

According to this sense, therefore, the reasoning of St. Thomas proceeds. For since that cannot be brought about through some instrument to which the proper action of the instrument in no way extends—namely, neither by way of introducing a form, nor by way of disposing the matter or subject in some way, nor by way of acting in some way upon that patient; and the proper action of a celestial body can in no way extend to the change of the intellect and the will, namely, either by introducing the principal form, or by disposing through directly acting upon the intellect and the will itself, as was shown above ⁶: it manifestly follows that a celestial body cannot be the instrument of a moving soul for changing the intellect or the will.

Nor is what must be proved assumed. Because what must be proved is that the heaven cannot be the cause of our choices as an instrument of a moving soul. But what is assumed is that the heaven by its own proper action cannot reach the intellect and the will: which is far different from the conclusion. And it is like someone proving that a bench cannot instrumentally be made from iron by a saw, because the proper action of a saw, which is to cut and divide, cannot reach iron.

2. Moreover, what is objected concerning a sacrament causing a character in the soul does not stand in the way. Because we must speak in one way of an instrument of divine power, and in another of an instrument of created power. For a created power, since it does not use an instrument except for acting, presupposes in the instrument which it uses for some effect a natural power by which it can reach the patient upon which it intends to act; otherwise it would not use one instrument rather than another. Whence we see in artificial things that different instruments are fitted to different effects, and according to the diversity of the matter upon which art intends to work, different instruments are taken which can reach the matter by their action. We see the same also in natural things. — But the divine power uses sacraments not only for acting, but also for signifying. Whence by theologians they are placed not only in the genus of cause, but also in the genus of sign. Therefore it does not presuppose an active natural power in them by which they can act upon the soul, in which God intends to cause grace through them; but it presupposes in them the fittingness of their natural action for signifying the action of God upon the soul, and of their effects for signifying the divine effect; while the power by which they can work upon the soul it confers upon them supernaturally. Just as, because baptismal water through its natural action, which is to wash and cleanse the body, is a fitting sign of the spiritual washing and cleansing which takes place in baptism through grace, therefore God assumes it as an instrument for causing grace, giving it a supernatural power by which it can, while exercising its natural action concerning the body, also supernaturally introduce into the soul some disposition to grace; just as He also gives to the fire of hell a power of detaining souls, which no created power can give it. Therefore the reasoning of St. Thomas proceeds excellently in the present case, where it is a question of an instrument of created power; but it would not proceed concerning an instrument of divine power.

3. Therefore when Capreolus, in IV Sent., d. 1, q. 1 ⁷, responding to the argument of Durandus, says that it is not universally true that an instrument acts naturally, and by its own power, in some action concerning whatever matter concerning which it acts supernaturally and in the power of another, if this is understood not to be universally true on account of an instrument of divine power, it is well said. If, however, it is understood not to be universally true because there is also some instrument of created power that can have no natural action concerning the matter concerning which it operates in the power of a natural agent, I do not think it is well said. For the reasoning set forth here could not, as was argued ⁸, be saved. Nor could the reasoning set forth in De Veritate, q. 5, a. 10, ad 4 be saved, by which St. Thomas argues that, because an instrument of a spiritual agent does not act through spiritual power except because it acts through corporeal power, while according to corporeal power a celestial body acts only upon a body, therefore the action of a celestial body which is according to spiritual power also cannot reach to the soul.

V. Secondly ⁹. If one human soul impresses something upon another human soul through a corporeal operation ¹⁰, such a corporeal action does not arrive at the other soul except by means of the body. This is clarified by the example of the manifestation of understanding through a signifying voice. — Therefore, if a celestial soul impresses anything through corporeal motion, that action does not arrive as far as our soul except through a change of our body. But that is not the cause of our choices, namely a sufficient one, but an occasion only ¹¹. Therefore etc. — The first consequence is proved. Because a particular agent cause in acting bears the likeness of a universal cause, and is its exemplar.

VI. Thirdly. To a celestial body, which is posited to be moved by a conjoined soul, our body is nearer than our soul. Therefore the change of the celestial body, proceeding from its soul, does not reach to our soul except by means of the body. Therefore the motion of the celestial body cannot be the cause of our choice, namely directly, through the fact that it is from a soul.

The antecedent is proved. Because our soul has no order to a celestial body except by means of the body. A sign of which is that separate intellects have no order to a body: except perhaps of a mover to the moved. — But the first consequence is proved. Because, since the mover and the moved must be together, motion must arrive from the first mover to the ultimate thing that is moved in a certain order; namely, so that the mover, through that which is proximate to it, moves that which is distant from it. — The second consequence is also proved. Because the soul is not moved at the motion of the body except per accidens; nor does choice follow the change of the body, except by way of occasion.

2. For the clarity of this reason, it must be considered that the order of proximity of movable things to the first thing that moves is not an order of position, but is an order of mutability according to the constitution of nature: so that that, namely, is called nearer to the first mover which is by nature adapted to be moved by it earlier, whereas that is called more remote which is by nature adapted to be moved by it later. Whence something is so much the more distant from the first mover, the later, according to the order of nature bestowed upon things, it is by nature adapted to be moved by it, and through the more media its action must reach to it. But our body is the medium between the celestial body and our soul according to this order: since the soul itself has no order to the celestial body except because it is united to the body. A fitting sign of which St. Thomas adduces, because an intellectual substance separated from the body has no such order to a celestial body; on the contrary, it is compared to it rather as mover to moved. For this reason the change of the celestial body, even when brought about by the power of a soul, does not arrive at the soul except by means of the change of the body; concerning which it was shown above ¹² that it is only a certain occasion of our choice, not however a sufficient cause. And in this consists the reasoning of St. Thomas.

VII. Fourthly. According to the position of Avicenna, and of certain other philosophers, the agent intellect is a separate substance, acting upon our souls inasmuch as it makes things understood in potency to be things understood in act. But this it does through abstraction from all material conditions. Therefore that which directly acts upon the soul does not act upon it through corporeal motion, but rather through abstraction from everything corporeal. Therefore etc.

Note that this reason is persuasive only ad hominem to a follower of Avicenna. Because if the agent intellect, according to Avicenna, is a separate substance, and acts upon our soul by causing in it understood species abstracted from material and corporeal conditions, it is an evident sign that, if anything acts directly upon our soul, it does not act upon it through corporeal motion. It is not, however, an absolutely conclusive reason: because according to Aristotle and St. Thomas it is false, as was shown above in the second book ¹³, that the agent intellect is a separate substance.

Finally St. Thomas says that by the same reasons it could be proved that the motion of the heaven is not the cause of our choices through the power of a separate substance.