Commentary Aristotle Physics
Lecture 12. The argument of those who deny that nature acts for an end
We must explain, then, that nature belongs to the class of causes that act for the sake of something; afterward, [we must explain] about the necessary and its place in physical problems, for all writers ascribe things to this cause, arguing that, since the hot and the cold and the like are of such and such a kind, therefore certain things necessarily are and come to be—and if they mention any other cause (one, “friendship and strife,” another, “mind”), it is only to touch on it and then say good-bye to it.
A difficulty presents itself: why should not nature work neither for the sake of something nor because it is better so, but just as Jupiter rains, not in order to make the corn grow, but of necessity?
What is drawn up must cool, and what has been cooled must become water and descend, the result of this being that the corn grows. Similarly, if a man’s crop is spoiled on the threshing floor, the rain did not fall for the sake of this—in order that the crop might be spoiled—but that result just followed.
Why, then, should it not be the same with the parts in nature, such as that our teeth should come up of necessity (the front teeth sharp, fitted for tearing, the molars broad and useful for grinding down the food) since they did not arise for this end, but it was merely a coincident result? And so [we might ask] with all other parts in which we suppose that there is purpose.
Then, wherever all the parts came about as just what they would have been if they had come to be for an end, such things survived, being organized spontaneously in a fitting way; but those that grew otherwise perished and continue to perish, as Empedocles says his “man-faced ox-progeny” did. Such are the arguments (and others of the kind) that may cause difficulty on this point.
250. Having shown that natural philosophy demonstrates from all the causes, the Philosopher here clarifies certain things that he had assumed: that nature acts for an end and that, in some things, necessity is not from the causes that are prior in being (which are the matter and the moving cause), but from the posterior causes, which are the form and the end.
Concerning this, he makes two points.
First, he states his intention;
second, at “a difficulty presents itself” (198b16; [251]), he develops his position.
He therefore says first (198b10) that it must be pointed out that nature is among the number of causes that act for the sake of something. And this is important with reference to the problem of providence. For things that do not know the end do not tend toward the end unless they are directed by one who does know, as the arrow is directed by the archer. Hence, if nature acts for an end, it is necessary that it be ordered by someone who is intelligent. This is the work of providence.
After this, it must be pointed out how necessity is present in natural things. Is the necessity of natural things always from the matter, or is it sometimes from the matter and the mover, or sometimes from the form and the end?
It is necessary to make this inquiry for the following reason. All of the ancient natural philosophers, when giving the reason for natural effects, reduced such effects to this cause, namely, that it is necessary for these things to happen because of matter. For example, since heat is by nature what it is and naturally produces a certain effect (and in like manner cold and other similar things), then those things that are caused by them must come to be or exist. And, if some of the ancient natural philosophers touched upon some cause other than the necessity of matter, they have no reason for taking any glory from the fact. For after such causes were posited by them—for instance, intellect, which Anaxagoras posited, and friendship and strife, which Empedocles posited—they did not use them except in certain general instances, such as in the constitution of the world. But they omitted such causes when discussing particular effects.
251. Next, at “a difficulty presents itself” (198b16), he develops his position.
First, he asks whether nature acts for the sake of something;
second, at as regards what is “of necessity” (199b34; [269]), how necessity is found in natural things.
Concerning the first part, he makes two points.
First, he gives the opinion and argument of those who hold that nature does not act for the sake of something;
second, he disproves this position, at “yet it is impossible” (198b34; [255]).
252. Concerning the first point, it must be noted that those who held that nature does not act for the sake of something tried to confirm their position by denying that in which nature is most clearly seen to act for the sake of something. That which most strongly demonstrates that nature acts for the sake of something is the fact that, in the operation of nature, a thing is always found to come to be as good and as suitable as it can be. Thus, the foot is made in a certain way by nature so that it may be suitable for walking. Hence if it falls short of this natural disposition, it is not fit for this use. And the same is true of other instances.
And, since they tried especially to oppose this point, Aristotle says (198b16) that it can be objected that there is nothing to prevent nature from not acting for the sake of something or from doing what is always better.
For at times, we find that, from some operation of nature, some utility results that nevertheless is not the end of that natural operation, but merely happens to occur. Thus, we might say that Jupiter rains—that is, God or universal nature—but not for the purpose that grain should grow.
Rather, rain results from the necessity of matter. For it must be that, in the lower regions, because of the closeness of the heat of the sun, vapors are drawn out from the water. Having been carried above because of the heat, when they arrive at the point where heat is lacking because of the distance from the place where the rays of the sun are reflected, it is necessary that the vaporized water that is going up freeze at that very point. When the freezing is completed, the vapors are changed into water. And, when water has been generated, it must fall down because of its weight. And, when this takes place, it happens that the grain grows.
Nevertheless, it does not rain so that grain might grow. For in the same way, grain might be destroyed in some place because of rain, as when grain is gathered on a thrashing floor. Nevertheless, rain does not fall in order to destroy grain; rather, this happens by chance when rain falls. And, in the same way, it seems to happen by chance that grain accidentally grows when rain falls.
Hence, it seems that there is nothing to prevent this from being true also in regard to animals, which seem to be disposed for the sake of some end. For example, one might say that, because of the necessity of matter, some teeth—namely, the front teeth—happen to be sharp and suitable for cutting food, and the molars happen to be broad and useful for grinding food.
Nevertheless, nature did not make the teeth such and such for the sake of these utilities. Rather, after teeth have been made by nature in such a way as they develop from the necessity of matter, it is accidental that they acquired such a form. And, once this form exists, this utility follows. And the same thing can be said of all other parts that seem to have some determinate form for the sake of some end.
253. But one might say that such utilities follow always or in many cases, and what is always or in most cases suitable exists by nature. In order to forestall this objection, they say that, from the beginning of the formation of the world, the four elements were joined in the constitution of natural things, and thus the many and varied dispositions of natural things were produced. And, in all these things, only that which happened to be suitable for some utility, as if it were made for that utility, was preserved, for such things had a disposition that made them suitable for being preserved not because of some agent intending an end, but because of that which is per se vain, that is, by chance. On the other hand, whatever did not have such a disposition was destroyed, and is destroyed daily. Thus Empedocles said that, in the beginning, things that were part ox and part man were generated.
254. Therefore, because of this argument, or because of some other similar argument, some will have a difficulty on this point. But in regard to this argument, it must be noted that they use an unsuitable example. For although rain does have a necessary cause in regard to matter, it is nevertheless ordered to some end, namely, the conservation of things generable and corruptible. For in inferior things, mutual generation and corruption are for this purpose: that perpetual existence be preserved in them. Hence, the growth of grain is poorly taken as an example. For a universal cause is referred to a particular effect. And it must also be noted that the growth and conservation of growing things on earth occur in most cases because of the rain, whereas their corruption occurs in few instances. Hence, although rain is not for their destruction, it does not follow that it is not for their preservation and growth.