Commentaria in Summam contra Gentiles, Liber III

Having shown that every agent acts for an end, St. Thomas now shows that every agent acts for the sake of the good ¹. Concerning this, however, he does two things: first, he shows the proposition; second, he infers a corollary, in the following chapter.

As to the first, he proves that Every agent acts for the sake of the good.

I. And first thus. Every agent tends toward something determinate. Therefore toward something suitable to itself: for it would not tend toward it except on account of some suitability. Therefore it tends toward the good: because that which is suitable to something is good for it.

Note that every agent acts toward something determinate from an inclination or direction following the form through which it acts. But a form directs only to something similar and conformed to itself. Therefore that determinate thing on account of which the agent operates is similar, conformed, and suitable to the agent insofar as it acts by such a form. And upon this is grounded the first consequence of this reasoning.

II. Second. The end is that in which the appetite of the agent or mover, and of that which is moved, rests. Therefore every motion and action is for the sake of the good. — The consequence is proved. Because it belongs to the ratio of the good to terminate appetite, as is evident from its definition.

But it seems that this reasoning does not hold: because it argues from pure affirmatives in the second figure, arguing thus: The end is that in which appetite rests. The good is that in which appetite rests. Therefore the good and the end are the same. If therefore every agent acts for an end, it follows that it also acts for the sake of the good.

It is answered, according to the mind of the Commentator, II Phys., comm. 23; and IV Phys., comm. 33 and 42; likewise II De Caelo, comm. 23, that it is not unsuitable to use an argument in the second figure from two affirmative propositions when the major proposition is universally converted. And this is manifest per se: because then the syllogism is virtually in the first figure; for once the major is universally converted, the syllogism appears to be in the first figure. Therefore doctors, and indeed Aristotle himself, sometimes do not care to construct arguments explicitly in due form when from the evidence of the propositions the very form according to which it has to be constructed is apparent. In the present case, therefore, St. Thomas did not care about the due form, because the major proposition is universally convertible: for just as every end of an agent as such is that in which the appetite of the agent is quieted, so everything in which the appetite of the agent is quieted is an end. If to this the minor is subsumed, namely, The good is that in which appetite is quieted, it follows most appropriately in the first figure: Therefore the good is the end.

III. Third. Every action and motion is ordered in some way to being (esse). Therefore to the good. — The consequence is evident. Because this very thing that is being is good: namely fundamentally. A sign of which is that all things desire being.

Fourth. Every action and motion is for the sake of some perfection: either, namely, for the sake of the action itself, which is the second perfection of the agent; or for the sake of the perfection induced in the moved thing; toward which the mobile also tends, if it is a natural motion. Therefore it is for the sake of the good. — The consequence is evident. Because to be good is the same as to be perfect.

It must be noted, when it is said that toward the perfection introduced by the agent into the moved thing the mobile also tends if the motion is natural: that in natural motion both the agent and the mobile tend toward the perfection caused by the agent, insofar as each of them is inclined to it; but this happens in different ways. Because the agent is inclined to introduce it into the moved thing by the actuality of the form through which it acts: but the mobile, as such, is inclined to receive it from its natural potentiality. This does not happen in violent motion, where there is no natural potency in the mobile for that motion.

IV. Fifth. Every agent tends toward some act: because it acts insofar as it is in act. Therefore it tends toward the good: because every act has the ratio of good, since evil is not found except in a potency falling short of act.

Sixth. An agent through intellect does not determine an end for itself except under the aspect (ratio) of the good: because the intelligible does not move except under the aspect of the good, which is the object of the will. Therefore also an agent through nature: because, although an agent through intellect determines an end for itself, an agent through nature does not, since it does not know the ratio of the end, but is moved to an end determined for it by some intellect.

Here two things are to be noted. The first is, that the intelligible is not therefore said not to move except under the aspect of the good as if it moved the intellect itself under the aspect of the good: for this would be false, since the ratio of the good is not the formal ratio of the object of the intellect, but rather the ratio of the true. But this is said in relation to the appetite of the one determining an end for himself through intellect. For an agent through intellect does not determine for itself an end on account of which it acts except because it proposes to itself that on account of which it wills to operate, and from whose volition it is moved to operate. And thus it is necessary that the intelligible which it determines for itself as an end move its appetite before it proceeds to operation. But the intelligible does not move appetite except under the aspect of the good.

The second is, that not determining an end for itself is common both to agents without knowledge and to brute animals acting from knowledge. Therefore St. Thomas includes both of these under the name of agent through nature. For although brute animals have some knowledge of that thing which is the end, from which they are moved to operate, nevertheless they do not know that thing under the ratio of end, since they do not know what an end is, as has been shown in the preceding ².

V. Seventh. All things flee evil, both agents through nature and agents through intellect: which is evident because they resist corruption, which is an evil, as much as they can. Therefore etc. — The consequence is proved. Because it belongs to the same ratio to flee evil and to desire good: just as not to be moved downward and to be moved upward.

Concerning this proposition, It belongs to the same ratio to flee evil and to desire good, it must be noted that they are not therefore said to be of the same ratio as if to flee and to desire or seek were one and the same act: but because they accompany each other. For no one flees evil except on account of the appetite for some good which is taken away by such evil: just as no one flees death except because he desires life; and a light body does not recede from a place below naturally except because it naturally desires to be moved upward.

VI. Eighth. In the works of nature we see either always or for the most part what is better: as is apparent in plants and the parts of animals. And this is not from chance. Therefore a natural agent intends what is better. And much more manifestly an agent through intellect. Therefore etc. — The minor is evident. Because things that occur always or frequently are not casual or fortuitous, but rather those that happen in fewer instances.

Note here, from II Phys.³, that not only when an agent produces what happens for the most part does it act for an end, but also when it produces what happens in the lesser part. For chance or fortune does not exist except in actions that are done for the sake of some end. For although nature does not intend the effect which happens in the lesser part, at least primarily and per se, nevertheless it does not produce it except when it acts toward that which happens for the greater part, and when it cannot arrive at this because of some impediment, it produces that which happens rarely.

Note also that an agent through intellect does not always or for the greater part produce what is absolutely better, but what is better in comparison to the extrinsic end that it intends: just as a builder does not make the greatest and best house that could be, but one that is suitable for the inhabitants for whose habitation he makes it.

Ninth. That which is moved tends to the good: because it tends from potency to act. Therefore also the agent and mover. — The consequence is evident. Because, since everything that is moved is led to the term of motion by the agent and mover, the mover and that which is moved must tend to the same thing, insofar as it is moved.

VII. The conclusion is confirmed by the authority of those who say that the good is that which all things desire; and of Dionysius, chapter IV of De Div. Nom., saying that all things desire the good and the best.

It must be noted concerning this chapter and the preceding one, that by proving that every agent acts for the sake of the good and for the sake of an end, St. Thomas does not intend that the agent acts for the sake of another good or for another end distinct from itself, but speaks absolutely: whether, I say, the agent acts for itself or for another, as for an end.