Commentaria in Summam contra Gentiles, Liber III

After St. Thomas has shown that God can work apart from the order of nature, he wishes to determine concerning those things which are thus done by God apart from the order of nature¹.

Concerning this, moreover, he does two things: first, he determines concerning them in relation to nature; second, in relation to the character of a miracle, in the following chapter.

I. As to the first, this conclusion is set down: Although God sometimes works something apart from the order implanted in things, yet He does nothing contrary to nature.

It is proved first. God is related to all things as the mover to the moved, and as what is active to that which is in potency. Therefore whatever is done by God in created things is not contrary to nature. — The antecedent is proved. Because God is pure act, whereas all other things have something of potency admixed. — The consequence is proved. Because if something is imprinted by an agent into that which is in potency according to natural order with respect to that agent, it is not contrary to nature simpliciter, even if it is sometimes contrary to the particular form that is corrupted by an action of this kind. This is shown in the generation of fire when air is corrupted.

2. Concerning the proof of the antecedent, it must be noted that, since every agent acts inasmuch as it is in act, each thing acts only so far as it is in act: for we see that fire, which is more actual and more formal than the other elements, is also more active than they. Similarly, each thing is acted upon inasmuch as it is in potency: and the more a thing is in potency, the more passive it is. Therefore that which is act simpliciter, altogether excluding all potency and including all actuality, is related to each thing having something of potentiality as active to passive, and as motive to movable: namely, as containing in itself the act to which each thing is in potency. Therefore St. Thomas proved very well that God is related to all things as motive to movable, and as active to that which is in potency, from the fact that He is pure act, namely, in no way contracted or limited by any potency, whereas all other things have something of potentiality admixed.

3. Concerning the inferred consequent, it must be considered that for something to be done contrary to nature is nothing other than for it to be done contrary to the order and inclination of some nature. Something is therefore said to be simpliciter and universally contrary to nature when it is contrary to the entire order and inclination of every nature whatever. But it is said to be contrary to some particular nature when it is contrary to the order and inclination of that nature. What God does in things, therefore, can indeed be contrary to some particular nature, inasmuch as that which is done is contrary to the order and inclination of the proper form of some nature; but it cannot be contrary to nature simpliciter and universally, since it is done according to the order and disposition of the most universal nature, which is God, from whom each thing has its proper order and its proper action. And the inferred conclusion is understood in this sense.

4. For the evidence of what is assumed for the proof of the consequence, it must be observed that something is said to be in potency according to natural order with respect to some agent, when from its own nature it has the capacity to be receptive of some form from such an agent, or of some motion. And therefore if some form or some motion is received in it from such an agent, that is not said to be done simpliciter contrary to nature, since it is according to the natural order of the patient to the agent: although it can be contrary to the natural inclination of that form. Just as, in the example of St. Thomas, when fire is generated from air by fire through the corruption of that air, such generation, nor such corruption, is not said to be simpliciter contrary to nature: indeed it is natural, because, according to natural order, air is naturally apt to be corrupted by fire, and is naturally apt so that fire can be generated from it through the action of fire. Yet such corruption is in some way contrary to nature, inasmuch as it is contrary to the inclination of the form of air: in which sense it is said in II De Caelo², that corruption, and old age, and every defect is contrary to nature.

II. Secondly. All things that are after God are as it were certain instruments of His. Therefore it is not contrary to nature when created things are moved in any way whatsoever by God. — The antecedent is proved. Because God is the first agent. — The consequence: because, since instruments have been instituted to serve the action of the principal agent, it is not contrary to the nature of an instrument to be moved by the principal agent.

For the evidence of this reason, it must be considered, from the teaching of St. Thomas in the Fourth Book, d. I, q. 1, a. 4³; and d. IV, q. 1, a. 1, and in many other places⁴, that it belongs to the notion of an instrumental agent to be a moved mover; and every cause that does not move unless moved has the character of an instrument. Therefore, since a secondary cause does not move unless moved by the first, it follows that it has the character of an instrument with respect to the first. Therefore St. Thomas proves very well that all things that are under God are as it were His instruments, because He is the first agent.

2. But this reason seems not to conclude. For someone could say: Although every secondary cause is an instrument of the first cause, yet it does not follow that it is not moved contrary to nature however it may be moved: because, since different instruments are proportioned to different effects, if anyone uses an instrument for something to which it is not proportioned, it is contrary to the nature of such an instrument to be so moved.

He answers that an instrument, inasmuch as it is the instrument of some principal agent, is always proportioned to the action that the principal agent intends: hence St. Thomas says here that the matter and form must be such as to be suited to the action of the principal agent. Hence if someone wished to use the instrument of some art for something to which it was not proportioned, it would no longer be an instrument with respect to that agent, as not serving him. But God created all things in such a way that they are instruments for Him, and serve the action which He has determined to exercise upon creatures, whether He has determined to effect something in them frequently or rarely. And therefore, however created things may be moved by God, they are not disproportionate to that motion: since they were instituted by God for this, that they might at some time be moved by Him in such a way, and they obtained such a nature from God that they could be moved by Him in such a way. Therefore nothing is done by God in them that is simpliciter contrary to nature: although, as was said, it is sometimes contrary to the proper inclination of some form.

Hence to the argument it is said that, although different things, which are instruments of the divine power, are proportioned to different proper actions and motions according to the inclination of their proper form, and one thing is disproportionate to the action of another; yet inasmuch as each one is an instrument of the divine power, none is disproportionate to the action and motion which God intends to effect in it.

III. Thirdly. The motions that are in lower bodies from the impression of the higher are neither violent nor contrary to nature: as is evident in the ebb and flow of the sea. Therefore, much more, that which is done by God in any creature cannot be said to be violent or contrary to nature.

2. It must be noted in this place that, just as all created things are compared to God as instruments, so also lower bodies are instruments of the higher, inasmuch as they do not move or operate unless moved by the higher. Hence lower bodies of this kind can be considered in two ways: in one way, inasmuch as they are such bodies, having such a form and such a natural inclination; in another way, inasmuch as they are instruments of the celestial bodies, naturally apt to be moved by them according to their intention. What is done in them by celestial bodies, therefore, is natural to them inasmuch as they are instruments of celestial bodies: for it is natural to an instrument to be moved by the principal agent. Yet it can be unnatural inasmuch as they are such bodies, having such a form and such an inclination, which is toward the opposite. As we say concerning the motion of the ebb and flow of the sea: for this is natural to the water of the sea inasmuch as it is an instrument moved by a celestial body; but it is contrary to nature for it inasmuch as it is a heavy body naturally tending toward the middle.

3. It must also be observed that St. Thomas assigns no other cause for the ebb and flow of the sea than the impression of a celestial body, because in this part he followed the opinion of Albumasar in Book II of the Greater Introduction, and of the Commentator on III De Caelo, who assign no other cause besides this. — Others, however, assign other causes. For a certain Adelard, as Pico relates in the third book of Against the Astrologers, chap. XV ⁵, from the opinion of the Saracens, says that the cause of this motion is that, when the arms of the sea hasten to meet one another and flow together with a swift rush, falling short of that natural motion on account of the obstacle of mountains, or even the layout of the land, they are carried back to the upper place, whence they begin to be moved. — Others ⁶ trace this incoming and receding of the sea to vapors and winds stirred up in the water, by whose motion and impulse the water is agitated and grows warm, and therefore seeks a wider place in which to spread itself, with the help also of upper winds, which, driving the top of the water to the lower parts, meet the internal state and are driven by them to the upper parts, whence it happens that the water, bursting forth, abounds and swells. But when that force of the spirits grows slack, the vapors having been dissolved, the waters subside and, contracting into narrow places, withdraw from the occupied places.

It must also be noted that among those who attribute this incoming and receding of the sea to the impressions of the heavens, there is a difference. For there are some whom it pleases that the increase and decrease of light in the moon is the cause of this thing. — To others, however, and also to St. Thomas in the Treatise On the Hidden Operations of Nature ⁷; and De Potentia, q. vi, a. 1, ad 17, it seemed that this very thing is to be traced to the motion of the moon: namely, so that as it ascends, the water also ascends; but as it descends, the water descends.

4. Concerning what St. Thomas says, that the natural motion of water is only toward one direction, namely toward the middle, a doubt arises. For experience seems to be to the contrary. For, when the earth near water is dug out, we see the water itself ascend, and consequently recede from the middle. Which indeed seems to be natural to water: just as a heavy body also naturally descends when an impediment is removed.

He answers that the ascent of that water is not natural, but is caused by something driving it: whether it be other water, or something else. A sign of this is that, if a steeper place is dug out from the sides, it immediately descends into it.

IV. Fourthly. That is natural to each thing through which it is conformed to its measure. But the first measure of every nature is God. Therefore to each thing that is natural which is implanted in it by God. Therefore etc. — The major premise is proved. Because judgment is made concerning each thing through its measure. — The minor: because God is the first being, which is the cause of being to all things.

Fifthly. It is not contrary to the nature of an artifact if a craftsman works something otherwise in his artifact, even after he has given it its form. Therefore neither is it contrary to nature if God works something otherwise in natural things than the accustomed course of nature has. — The consequence is proved. Because all creatures are compared to God as artifacts to a craftsman.

The conclusion is confirmed by the authority of Augustine, XXVI Against Faustus.

It must be noted that these last two reasons conclude in the sense of the preceding ones: namely, that it is not contrary to nature simpliciter and universally if God works something in natural things otherwise than the accustomed course of nature has; but not that it is not contrary to the nature of some particular form, in the manner previously explained ⁸.