Commentaria in Summam contra Gentiles, Liber II

In the second place, Saint Thomas shows how, although all things depend on the divine will, which has necessity only from the supposition of its own purpose, nevertheless absolute necessity is not on that account removed from things, as though we were obliged to confess that all things are contingent ¹.

On this point he does two things: first, he proves that there are certain things in created things which are necessary to be simply and absolutely; second, he declares how this necessity is found in things ².

I. As to the first point, it must be noted that that a thing be necessary simply and absolutely can be understood in two ways. In one way, by comparison to its productive cause; and then a thing is said to be necessary when it is produced necessarily by its cause. And in this way, by comparison to God, no thing is necessary, although some things are necessary by comparison to their created cause. St. Thomas does not take necessity in this sense. — In the other way, as it is considered in its own nature; and then a thing is said to be necessary which, once posited in act, has nothing within itself whereby it could not be. The conclusion is to be understood in this second way.

It is proved first as follows. There are certain things in which there is no possibility of not being. Therefore, etc. — The consequence is evident, because those things in which there is no possibility of not being must be simply and absolutely necessary in their being. — But the antecedent is proved: because there are certain things in which either there is no matter, or, if there is matter, it is not capable of another form. Such things do not have a potency for not being; just as, conversely, those things in which there is matter that is in potency to another form can not be.

Note that no agent, by its action, intends first that something not be; but if it makes something not be, this is because it intends some being with which the preceding being cannot stand. Therefore, that something have in itself what enables it to be made not to be by some agent cannot come about except because there is in it some receptive potency for another esse. And since every esse is from some form, therefore it is necessary that there be in it a receptive potency for another form. Where, then, this is not present, that thing does not have in itself that from which it could not be. And this is the foundation of this argument.

But if anyone were to say that the antecedent of this argument is false, because things that are made from nothing tend toward nothing insofar as they are of themselves, and all things were created from nothing—Saint Thomas replies that this does not destroy the truth of the antecedent. For just as things are not made from nothing except according to the power of the agent, so too there is no power toward non-being (that is, toward being nothing at all) inherent in created things themselves; rather, the power resides in the Creator to give them esse or to cease infusing it.

II. Second. Things proceed into esse from the divine will. Therefore they are such as God willed them to be. Therefore, from the fact that things are produced by God through will, not through necessity of nature, it is not ruled out that he willed some to be of necessity and others contingently, so that there may be an ordered diversity in things. Therefore etc.

Third. That something be necessary simply does not conflict with the notion of created esse: since it is not repugnant that some necessary thing have a cause of its necessity, as do the conclusions of demonstrations. Therefore, etc. — The consequence is proved. Because it pertains to the divine perfection that he impressed his likeness upon created things, except in regard to those things which are repugnant to what it is to be a created being. This is proved: because it belongs to a perfect agent to produce what is like itself as far as possible.

But it seems that this argument does not conclude. For by means of it one could prove that God produced another world more perfect than this one: from the fact, I say, that it belongs to a perfect agent to produce something like itself as far as it can.

It is answered that by this argument it is not proved that necessary beings are produced of necessity, but only that their creation is fitting and involves no repugnance. For it is fitting that God, who is a perfect agent, produce what is like himself with respect to the universal modes of being, which are the contingent and the necessary (for each of these modes has some likeness to God): so that, just as he is esse in the most universal sense according to perfection, so in created things he should produce all the most universal modes of being according to predication. But it is not thus fitting with respect to the production of another world.

Hence the proposition assumed, that it belongs to a perfect agent to produce what is like itself as far as it can, is understood not of necessity, if taken universally, but of congruence. Hence it is not introduced as though God, who is a perfect agent, must of necessity produce something like himself in whatever way he can as far as possible; rather, it is introduced to show that, just as natural agents, the more perfect they are, the more they produce what is like themselves and seek to assimilate to themselves what has undergone their action as far as they can, so it is fitting that God, who is the most perfect agent, produce what is like himself with respect to all the general modes of being that can exist in created things; nor does it conflict that necessary beings be produced by him, since it does not conflict with his esse that esse be created.

III. Fourth. The more a thing differs from God, the closer it is to non-being; and conversely, the more a thing is close to God, the more it recedes from non-being. But some existents are close to non-being precisely because in them there is a potency toward non-being. Therefore those things that are closest to God, and by this most remote from non-being, must be of such a kind that there is not in them a potency toward non-being. Therefore they must be necessary. — The consequence is evident. For, if affirmation is the cause of affirmation, and negation is the cause of negation ³ And, given an effect, it is necessary that the cause be posited. If, then, closeness to non-being is the effect of a potency toward non-being, remoteness from non-being will be the effect of the absence of a potency toward non-being; and, once the greatest remoteness from non-being is posited, the potency toward non-being must be removed.

IV. As to the second point ⁴, Saint Thomas shows how necessity is found in created things. Concerning which he does four things ⁵.

For first he shows that, in general, absolute necessity can be found in created things if they are compared to their proximate principles, but not as they are from the First Principle: namely because nothing prevents certain principles from being produced not of necessity, yet once these are posited, such an effect follows of necessity.

V. Second, he shows how necessity is found in things from their essential principles. And he says two things. The first is that what belongs to a thing by reason of its essential principles has absolute necessity: for without its essential principles, which are matter and form, things cannot have esse.

The second point is that from these principles absolute necessity is found in things in three ways. First, necessity is found in relation to the esse of that whose principles they are. For some things are necessarily corruptible, on account of the condition of matter: because matter, insofar as it is such, is a being in potency; and what can be can also not be. — But some are necessarily incorruptible, on account of form. For either they are forms not in matter: and thus there is in them no potency to non-being, but by their form they are always in the power of being; as is the case with separate substances. Or the form matches the whole capacity of matter, so that no potency remains for another form: as is the case with celestial bodies. — In those, however, where the form does not complete the whole potency of matter, there still remains a potency to another form. And therefore there is in them no necessity of being, but the power of being follows upon the victory of form over matter: as is evident in the elements and elemental compounds. For the form of an element does not reach matter according to its entire power: since it is receptive of the form of one element only by being subjected to one part of the contrariety. The form of a mixture, however, reaches matter insofar as it is disposed by a determinate mode of mixture. Now the same subject must be that of contraries, and of all the intermediates which arise from the commixture of extremes. Therefore all things that either have a contrary or are made of contraries are corruptible. But those that are not of this kind are everlasting, unless they are corrupted per accidens: as is the case with celestial bodies.

Second, necessity is found by way of order to the parts of matter or form, should it happen that such principles are not simple in certain cases: thus from matter it is necessary that man have within himself each of the elements and humors, and from form it is necessary that he be both animal and rational, if he is animal, rational, and mortal, and this is his form.

Third, necessity is found by way of order to a property consequent upon matter and form: just as it is necessary that a saw be hard from its matter, and that a man be receptive of discipline from his form.

VI. Concerning that proposition laid down in the first mode of necessity, namely, That which can be can also not be, it must be understood that, since one thing cannot have except a single substantial esse, it is necessary that what receives some substantial esse lose the esse it has, and consequently be under the non-being of that thing: for the matter of fire, when it receives the form and esse of air, loses the form and esse of fire, and remains under the non-being of fire; because the same matter cannot at once have the esse of fire and the esse of air. And therefore it is true that everything which has in itself something receptive of another form and another esse can not be: for when that thing receives another esse, this thing of which it was a part will no longer be. Hence the sense of that proposition is: Everything which can be, that is, which has in itself a potency receptive of an esse which it does not have, can also not be. — But what I have said about substantial esse must also be understood of accidental esse. For it is universally true that everything which has a potency receptive of the esse of anything whatsoever can also not be with respect to the non-being conjoined to that esse which it receives: what can be black can not be white, and so on for other cases.

2. It must also be noted that when it is said of separate substances that they are always in the power of being, while in corruptible things the power of being follows upon the victory of form over matter, this power of being is understood to be in the separate substances after they have been brought into act, as will be said below ⁶. For the power of being follows upon a thing already existing in act, just as does the power of operating: what does not exist cannot operate, nor can it even conserve its esse or its duration. Therefore, since they are in act, they have the power to be forever, because there is in them no potency toward non-being. Corruptible things, however, do not have the power to be forever, because they have a potency toward non-being; but they have the power to be as long as there is victory of form over matter.

3. Concerning that proposition as well, "The matter of the elements does not become receptive of the form of one element except by being subjected to one of the two parts of a contrariety," it should be noted that it can have a twofold sense. One is that one of the contraries is the reason why matter receives the other. And this sense is not true, nor is this what is intended: for heat is not the reason why matter receives cold, since heat expels it. — The other sense is that matter is not receptive of the form of one element unless it is under the contrary form. For, since the form of an element has in some way a contrary, and the same matter is the matter of contraries, that matter which does not have within itself the contrary of an element's form is not receptive of that form; but if it has the contrary form, it will be receptive of the other. And this sense is true, and this is what is intended: for what is conveyed by that way of speaking here is not the formal reason of receiving, but the condition of matter receptive of an element's form.

4. Concerning the example given in the second mode of necessity, note that when it is said that the form of man is "rational mortal animal," and that this form has parts, this is not said of the intellective soul itself, which is the physical and natural form, but of the definition, which is the form according to reason and logical consideration. For the latter has parts. And therefore it is necessary that each of its parts belong to man.

VII. Thirdly ⁷, he shows how such necessity is found in things from agent causes. And he says three things. The first is that, with respect to the very act of acting, there is a necessity like the necessity of an accident which a thing has from its formal principles. And that in the genus of immanent actions, there is necessity with respect to the actions themselves: for from the form by which the sense is in act, it is necessary that the sense sense; and when the intellect is in act through an intelligible species, it is necessary that it understand. But in the genus of transitive actions, from the form of the agent there follows a necessity of action with respect to the power of acting: for it is necessary that, if fire is hot, it have the power of heating; but there does not follow a necessity of the action itself in itself, because the agent can be impeded from acting. Nor does it matter, for the purpose at hand, whether the agent is one alone sufficient for the action through its form, or whether many agents must be gathered together for one action to be performed.

The second is that necessity is found in effects from the agent cause, concurring together with the disposition of the patient: namely, so that there be in the patient a potency for receiving, and in the agent a victory over the patient, such that it can transmute it. And then there follows either necessity of violence, if such an effect were against the natural inclination of the patient, as when a stone is thrown upward; or necessity of natural order, if it were not against the natural inclination, as in the motion of the heavens, likewise in the alteration of lower bodies by celestial bodies, and likewise in the generation of the elements. For the form to be introduced through generation is not contrary to prime matter, which is the subject of generation, although it is contrary to the form being cast off: for matter existing under a contrary form is not the subject of generation.

The third is that, if such a disposition of agent and patient, from which the effect follows of necessity, is absolutely necessary in the agent and the patient, there will be an absolute necessity in the efficient cause for producing such an effect: as in those things which act by necessity and always. But if it is not absolutely necessary, but can be removed, there will be no necessity from the efficient cause except on the supposition of the due disposition of each for acting: as in those things which do not act always but for the most part.

2. Concerning the example given in the first mode of this necessity, namely that an intellect existing in act through an intelligible species must understand, a doubt is raised. For, this being granted, it follows that the intellect understands all things at once whose species inform it. The opposite of which was shown in Book I ⁸.

It is also doubted concerning what was laid down in the second dictum, namely that matter existing under a contrary form is not the subject of generation. For its opposite seems to be said above ⁹, where it was stated that matter is not receptive of the form of one element except by being subjected to one of the other parts of contrariety.

3. To the first of these it is answered that this is understood of the intellect existing in complete act according to the intelligible species. Now it is in complete act through the intention of the will applying the intellect to understanding according to that species. But when that intention is removed, it is not in complete act. Therefore, while the intellect is thus in complete act, it is necessary that it understand (unless indeed there be a defect in the interior sensitive powers, which the intellect needs in order to understand): for no disposition is required on the part of the intelligible as it is in itself. But while it is in incomplete act, it is not necessary that it understand. Hence the consequence is denied: because the intellect is not informed completely by all its species at once.

To the second it is said that there is no contradiction. For Saint Thomas here speaks of the aggregate of matter and contrary form: for it is certain that a form introduced by generation does not have as its subject and recipient matter together with a contrary form. But above he speaks of matter itself alone: which must have a contrary form before it receives another form, if it is to be receptive of the form of one element; although in receiving that form of the element the contrary form is cast off from it.

VIII. Fourth, in ¹⁰, he shows how there is necessity in things from the final cause. And he says two things. The first is that, insofar as the end is first in the intention of the agent, in the same way there is necessity from the end and from the agent: because the agent acts insofar as it intends the end, both in natural and in voluntary agents.

The second is that from the end, insofar as it is posterior in esse, there is taken a necessity not absolute, but conditional.

2. For the clarification of the first statement, it must be considered that the end, insofar as it is in the intention of the agent, stands to the agent as a disposition of the agent, in that it moves him to act. And therefore the agent measures his actions by the end, just as by the form through which he acts. Now in natural agents the intention of the end is nothing other than the inclination of the natural form toward that end; and this inclination is really nothing other than the form itself with a certain respect and order toward something else. And therefore the same necessity in natural things arises from the form of the agent and from the end insofar as it is in the intention of the agent. For if there is necessity absolutely, with respect to the action or the effect, from the form of the agent, there is also necessity from the end so taken; but if the necessity on the part of the agent holds only under some supposition, there is also necessity from the end in the same way. — But in voluntary agents the intention of the end is said in two ways: namely, the apprehension itself, by which something is judged to be good and fitting, and therefore to be that for the sake of which something is to be done; and the inclination, which is the act of the will consequent upon such an apprehension. And because these have the character of one total form of the voluntary agent through which he produces the effect, just as the natural agent acts according to the condition of the natural form, therefore also in voluntary agents necessity is taken in the same way from the end and from the agent himself. For if the effect follows of necessity from the apprehension itself and the inclination of the will, there is likewise necessity from the end itself; but if the effect does not follow of necessity from such an apprehension, neither does it follow from the end. Similarly, if the apprehension itself and the inclination are necessary, the consequent effect will be necessary absolutely from the end itself. For the end in the intention of the voluntary agent is nothing other than the apprehension of the end itself and the inclination of the will toward it. On this account Saint Thomas rightly said without qualification that, the end being taken as it is first in intention, necessity is the same from the end and from the agent: namely, because this is universally true, both in voluntary and in necessary agents.