Lecture 8 — The vegetative principle: two errors refuted

Empedocles did not speak well here, adding that growth occurs in plants by their sending a root downwards because earth by nature is carried below, and also upwards because of fire.

Nor did he rightly understand up and down. For these are not the same for all things as for the universe; but roots of plants are like the head in animals, if it is permissible to say that organs are the same or different based on their works.

Besides, what holds fire and earth together if they are borne in contrary directions? They must come apart if there is nothing to prevent this. But if there is such a thing, it must be the soul and be also the cause of growth and nourishment.

Now, it seems to some that the nature of fire is simply speaking the cause of growth and nutrition; for it certainly seems to be the only one of the bodies and elements that is nourished and grows. Whence one will think this that is active in plants and animals.

It is in a certain way a joint cause, but not the cause simply speaking; rather, the soul is. For the growth of fire is infinite so long as there is anything combustible. But there are limitations to all things that are composed by nature, and a proportion of both their size and their growth. And this belongs to the soul, not to fire, and to the proportion more than to matter.

324. Empedocles did not speak well (415b28). The Philosopher has just shown that the activities we attribute to the vegetative power have their origin in the soul. (Lect. 7, nn. 318–23.) He now proceeds to refute two errors on this subject, which he deals with respectively in two sections;

the second of which begins at now, it seems to some that the nature of fire (416a9; [329]).

Concerning the first, he does two things.

First, he states the error;

and second, at nor did he understand (416a2; [325]), he attacks it.

Regarding the error itself, we should note that just as Empedocles explained other cases of purposeful arrangement in living things not by the intention of nature but from the necessity of matter—for example, he said that animals had the sort of feet they have, not in order to help them to walk, but because the matter of that part of their bodies happened to be disposed in that sort of way—so also the growth of living things he ascribed not to the soul but merely to the motion of light and heavy bodies. Observing that living things increase their size in different directions, for example, up and down—as is evident in plants, which thrust their roots down and their branches up—he said that the downward growth of plants is caused by the motion of earth in their composition, which is heavy and therefore naturally tends downwards, while their upward growth is caused by the motion of fire, which, being light, naturally tends upwards.

325. Aristotle, then, at nor did he (416a2), brings two arguments against this opinion of Empedocles.

First, he says that Empedocles did not understand up and down. To see what he means here, we should note that up and down and the other differences of position (before and behind, right and left) are differentiated in some things naturally, while in others they are merely relative to ourselves. For in things that have determinate parts as the natural principles of their various movements, the differences of these positions are based on nature itself.

Just as in the universe, heavy things are naturally carried to its middle, and light things are naturally carried to its circumference, so in the universe the up and the down are distinguished naturally, and the place to which light things are borne is called “up,” and that to which heavy things are naturally borne is called “down,” or “the middle.” And in living and mortal things as well, up and down are determined according to the motions of growth and decrease; for the upper is that part which takes in food, and the lower is the opposite part, which ejects superfluities.

326. Again, in some animals, before and behind are determined in relation to their senses, and the right and the left by their movements in space. But things that have no determinate part that is a principle or term of movement also have no differences of position naturally determined within them; these are fixed simply by the thing’s position relative to us. So is it with things without soul; the same pillar is said to be on the right or the left according as it is to the right or left of a man. Now, in certain living things, the natural upper and lower parts are determined in the same way as in the universe. It is so in man, whose upper part is turned toward the top of the universe and his lower part toward its bottom. But the reverse is found in plants, whose roots correspond to the head, for they are ordered to the same act (for as animals take in food by their mouths, which is in the head, so do plants by their roots). Now, organs are said to be the same or different if their works are so, which are their ends; hence the roots of plants are like the heads of animals, although they point downwards. Up and down, then, mean opposite things in plants and in the universe. But brute animals are different; their heads are turned neither up nor down in relation to the universe. This is what he means when he says that up and down are not the same for all things (that is, living things) as they are for the universe, that is, the cosmos.

327. But Empedocles took up and down to be the same for all living things and for the universe. For if the movement of growth, according to which the upper and lower are determined in living beings, followed the movements of the heavy and the light, according to which the same relations are determined for the cosmos as a whole, then up and down would mean the same in all living beings and in the cosmos. This is what led Empedocles to say that the roots of plants grew downwards.

328. The second argument against Empedocles begins at besides, what holds (416a6). To understand it, we should note that, because the elements in a mixture are present not actually, but by their power, or virtually, each of the elements does not have its proper movement. Rather, the whole mixture is moved with the movement of the element that predominates in it. If each, as Empedocles seems to have thought, retained its own proper movement, then, since the elements have natural movements in contrary directions, it follows that they would become totally separated from one another, unless something containing the elements prevented them from totally drifting apart. But what contains the elements so that they are not totally separated seems to be the chief cause of growth and nourishment.

But the increase of the body in its various parts is due to diverse motions of the elements. For one cannot imagine how there could be growth when the elements move in contrary directions unless the elements remain conjoined; for if they became separated, there would be division, not growth. Therefore in living things, that which contains the elements so that they are not entirely separated from each other is principally the cause of growth; but in living things, this is the soul, so the soul is the principle of their growth.

329. Next, at now, it seems to some (416a9), he states another theory. And concerning this he does two things.

First, he states it.

Second, at it is indeed (416a13; [331]), he disproves it.

Unlike the theory of Empedocles, which puts the cause of growth and nourishment in various elements, namely, fire and earth, this theory ascribes the cause only to fire.

330. The reason given is that the principle of anything’s passions or motion would appear to be whatever had such passions or motions in virtue of itself—for example, fire, being hot in virtue of itself, is the cause of heat in compound things, and earth, which is heavy in virtue of itself, is the cause of heaviness in these things. Now, of the elements, fire alone seems to feed itself and to grow, if we take these terms in a superficial sense. Therefore, fire alone would seem to cause growth and nutrition in plants and animals (416a9). But whether fire really feeds itself and grows will be made clear later. (Lect. 9, nn. 341–42.)

331. Then, at it is indeed (416a13), he disproves the aforementioned position. But it should be known that this position has some truth to it.

For all food has to be cooked, and this does occur through fire, so fire does act in a way for the sake of nutrition, and consequently for the sake of growth, not indeed as the principal agent (for the soul is this (416a13)) but as a secondary, instrumental agent. He says, then, that fire is in a certain way a joint cause of growth and nourishment as an instrument is a joint cause with the principal agent. But it is not the cause simply speaking, as the principal agent; rather, the soul is the cause in this way, as he goes on to show.

332. The principal agent in any action is that which imposes the limit and proportion upon what is done; this is clear in artificial things, like boxes or houses: the limit and proportion is fixed, not by the instruments used in the work, but by the art itself.

For the instruments are indifferent as to whether they are used to produce a thing of this shape and quantity or of that. A saw, as such, can be used to cut wood for a door or a bench or a house, and in any quantity you please; and if it cuts wood in this or that particular shape and quantity, this is due to the power of the art.

Now, in nature, things obviously have limitations and some determinate proportion of both their size and their growth (416a13). For as each species of thing requires its own proper accidents, so it needs its own quantity, though with some margin on account of material differences and other individual causes (for men are not all the same size, but nevertheless, there is some quantity so great that the human species cannot be extended beyond it, and some quantity so small that man cannot be found beneath it). Therefore, the cause of this determination of magnitude and growth is the principal cause of growth.

But this cannot be fire, because the growth of fire is not toward a determinate quantity; rather, it would spread to infinity if an infinite amount of combustible matter were available. Clearly, then, fire is not the principal agent of growth and nutrition; this belongs to the soul. And this is reasonable enough, for the determination of quantity in natural things is from the form—which is the principle of the species—more than from the matter. Now, the soul of a living body is to the elements it contains as form is to matter; therefore the limitations and proportion of both their size and their growth is more from the soul than from the fire.