Lecture 9 — The vegetative principle: nutrition

Since the vegetative and generative powers of the soul are the same power, it is first necessary to fix the nature of food. For it is by this activity that this power is distinguished from the others.

It would appear that food is a contrary to that which is fed; yet not everything is contrary to everything, but only such contraries as have not only generation from each other, but even their growth. For there are many things which originate from each other, but not all things (for instance, health comes from sickness). Nor, it seems, do all that do so nourish one another in the same way. For water is a food to fire, but fire does not feed water. And with simple bodies, this seems especially to be the case: that which feeds is one thing and that which is fed another.

But a difficulty arises here. For some say that anything is nourished by what is similar to it, just as it is increased thus. But to others, as we have said, it seems, on the contrary, that a thing is nourished by its contrary, as though like cannot be acted upon by like. But food is changed and digested, whereas in all things change is either to a contrary or to a mean state. Moreover, food is acted upon by that which is nourished, not the latter by the food, any more than a craftsman is acted upon by his material; but instead, this is acted on by him—the craftsman changing only from repose to activity.

It makes all the difference indeed whether food is considered as what it is at first or as what it becomes finally. But if as both, in the one sense as undigested, in the other as digested, then certainly both theories of food can be upheld; for as it is undigested, one contrary is nourished by the other; but insofar as it has been digested, like is nourished by like. Whence it is clear that both parties speak in one way correctly, and in another way incorrectly.

Since only what is alive is nourished, what is nourished is the ensouled body as ensouled. Wherefore food means something related to what is ensouled, and this not only accidentally.

Now, to be nutritive and to be augmentative are two distinct things. Insofar as something ensouled is a quantity, food is augmentative, but insofar as it is this particular thing and a substance, food is nutritive. For it preserves the substance, and this just so long as it is fed.

But it is productive of generation, not that of the one being nourished, but of such a one as the one nourished—for the former is a substance, and nothing generates its very self; rather, it only maintains itself.

Therefore, this principle of the soul is a power able to preserve what possesses it as a thing of such a kind; and food is preparatory to the activity; hence, it cannot exist deprived of food.

Since there are three factors: what is fed, that by which it is fed, and the one feeding; the one feeding is the first soul, that which is fed is the body containing it, and that by which it is fed is food.

But since all things are rightly named from their end, and the end is to have generated another being like itself, then the first soul is generative of what is like itself.

“That by which” in nourishment is twofold, as “that by which” in steering is the hand or the rudder: the one moving and moved; the other moving only. Now, of necessity all food must be such that it can be digested, and what effects digestion is heat. Hence every animate being has heat.

In outline, then, we have stated what nourishment is; the subject must be further examined later in its proper accounts.

333. Since the vegetative and generative (416a18). After showing that the activities attributed to the vegetative power have the soul as principle, the Philosopher proceeds to examine these activities. And about this he does three things.

First, he examines their object in itself, which is food.

Second, he shows how the activities of the vegetative soul and their object correspond, at since only what is alive (416b9; [340]).

Third, at wherefore this principle (416b17; [345]), he defines the powers that are the principles of these activities.

As regards the first point, he does three things:

first, he states the plan of the present argument;

second, at it would appear that food (416a21; [334]), he says what at first sight appears true about nutrition;

third, at but a difficulty, (416a29; [336]), he brings an objection against this.

In the first place, then, he observes that, as the vegetative and generative powers are included in the same general power of the soul, although the vegetative (that is, the nutritive) is a certain specific power distinct from the generative, we should discuss food, which is the object of the vegetative or nutritive power. For it is this activity, namely, of taking food, that characterizes this part of the soul as distinct from the intellectual or sensitive parts. For the other activities in this part of the soul presuppose taking food.

334. Then, at it would appear that food (416a21), he states in three points what appears at first sight with regard to nourishment.

First, food would always seem to be the contrary of the subject being nourished; and this is because food is changed into that which is nourished; moreover, generations are from contraries.

Second, however, it seems to be clear that not any contrary whatever can suffice for the account of food; rather, food must be among those contraries that have generation from each other.

For food is changed into the substance of the one fed; hence whatever contraries are within substance, according to which alterations occur, and are not generations, do not pertain to the account of food. For we do not say that the sick is the food of the healthy, nor white of black, or anything similar. (But how there can be a contrariety within substances is another question.)

335. Third, since growth seems to follow nourishment, the contraries must admit of growth from each other in this way. Whence, although water may be generated from fire and vice versa, yet we do not say that water is fed by fire. Yet we can say that fire is fed by water, inasmuch as there are wet liquids that come into the nourishment of fire. For when fire is converted into water, there appears to be a new coming-to-be of water; but a preexisting fire seems to convert into itself the wet thing for its own conservation and growth.

Among the elements, therefore, only fire seems to be fed and only water seems to be its food, insofar as all fluids and liquids pertain to water.

336. Then, at but a difficulty (416a29), Aristotle brings an objection against what he has just said.

And first, he raises an objection against both parts.

Second, he solves it, at it makes all the difference (416b3; [339]).

The difficulty concerns the statement that food must be a contrary. For some maintain that food should be like the subject fed. For food is the cause of growth, and therefore like ought to grow by what is like. For if food is assigned as something other, then it would not be the growth of the same thing but instead the addition of an extrinsic nature. Therefore, like, it seems, must be fed by like.

337. To others, however, it seems that food must, as we have said, be contrary to what is fed. And they are moved by two reasons.

First of all, food, being digested, is transformed into the subject fed. But all transformation is either to a contrary or to a mean state, as white into either black or grey. And an intermediate is a sort of contrary: for gray compared with white, is black, and compared with black, is white; for it combines both. Therefore, food is contrary to what is nourished, to that into which it is transformed.

338. Second, every agent is contrary to that on which it acts; like is not acted upon by like. But food is acted upon by that which is nourished: for it is transformed and digested. What is being fed is not acted upon by its food any more than an artist is acted upon by his material (for it is the material that is altered, not the artist, except accidentally, insofar as he goes from potency to act). It would seem, then, that food is contrary to what is fed.

Now, the first of these two reasons is drawn from the contrariety between the two terms of a change;

and the second reason is drawn from the contrariety between agent and patient. That which is fed and which itself acts upon the food is the term into which the food is transformed.

339. Then, at it makes all the difference (416b3), he solves the problem, saying that the answer depends on whether by food we mean what it becomes finally after the process of heating and digesting, or what it is at first before this process begins.

If “food” can be taken in both these senses—namely, as the digested food and as the not yet digested—then the two answers are both admissible. If it is taken in the latter sense, as undigested, then subjects are fed by their contrary, for this is what is acted upon and transformed; but if in the former sense, then like is fed by like, for an agent renders like what it acts upon, which at the end of this undergoing is made like the agent and, in this way, the food can augment that which it nourishes.

Thus both the above opinions were in one way true and in another way false.

340. Next, at since only (416b9), he shows how food is related to the activities of the vegetative soul:

first, to taking nourishment;

second, to growth, at now, to be nutritive (416b11; [343]);

third, to reproduction, at but it is productive (416b15; [344]).

First, then, he observes that nothing is nourished except what participates in life, but since everything that has life is ensouled, it follows that the body that is fed is ensouled. Now, food is in potency with respect to what is fed, for it is changed into this. It follows, then, that food, inasmuch as it is the object of nutrition, is something in potency to what is ensouled, through itself and not only accidentally.

341. Properly speaking, then, nothing is fed except what has a soul. Fire might seem to resemble in some way things that are fed, but it is not fed, properly speaking, as is clear from what follows. For that is properly said to be fed which absorbs something else in order to maintain its own being; and though this appears to happen with fire, it does not really happen. For once a fire has started, if you add combustible matter, a new fire starts in that combustible matter, but not in such a way that the new fuel maintains the fire already started before it was added. For example, by starting a fire in fresh wood you do not maintain the flame in the other wood already burning. For the total flame made up of many things ignited is not one simply speaking; rather, it is only one by aggregation, the way a heap of stones is one. And it is this sort of unity that gives to burning a certain likeness to taking food.

342. Ensouled bodies, on the other hand, are really fed; for food maintains life precisely where it already existed. This also is why only ensouled bodies truly grow; for each and every part in them is fed and increases, whereas things without soul increase only by addition of part to part; for what existed already does not increase, but rather, some greater whole is constituted by something else being added to it. But fire has a special likeness to living and growing things because fire has more of form than do the other elements, and its active power is more powerful. It seems, therefore, to feed and grow because it so obviously converts other things into itself.

343. Then, at now, to be nutritive (416b11), he relates taking food to growth, observing that while what is the object of nourishment as feeding and the object of growing as causing increase are the same in subject, nonetheless they differ in account. For food, we have seen, is in potency to the ensouled body, and the ensouled body is both a certain quantity and this particular thing and a substance.

Insofar as something is a certain quantity, the food reaching it, which is itself a quantity, causes growth and is called augmentative; but inasmuch as an ensouled body is this particular thing and a substance, it has the account of food. For it belongs to the account of food to maintain the substance of what is fed, which is required by the continuous using up of natural warmth and moisture. Hence, the substance of the thing fed lasts just so long as it is nourished.

344. Then, at but it is productive (416b15), he shows how food is suited to generation. And he also says that food is a cause also of generation. For seed, which is the principle of generation, is a residue of one’s food.

Yet food is not a principle of the generation of the one being nourished, but of another that is like in species to the one nourished; for the substance that is being nourished already exists and what exists cannot be generated. Nothing generates itself, because what generates already exists and what is generated does not exist yet. But something can act for its own preservation.

345. Next, at therefore, this principle (416b17), he concludes with a definition of the powers of the vegetative soul:

first, of the nutritive power;

second, of the whole vegetative soul, at but since all things (416b23; [347]).

About the first, he does two things.

First, we understand the definition of the nutritive power from what has already been said. (Lect. 8, n. 331.) Insofar as the nutriment preserves the thing nourished, this principle of the soul (namely, the principle of nourishment), is nothing other than the power by which the living being is able to preserve itself as such. But food is preparatory for this power’s activity, insofar as this power preserves its subject by means of food. And on account of this, whatever is deprived of food cannot survive.

346. And, having remarked that the principle of nutritive activity is a power whose principle is food, he goes on, at since there are three (416b20), to show how that power and the food itself differ as principles of nutrition. (Lect. 7, n. 323.) Nutrition, he says, involves three factors: what is fed; that by which it is fed; and the one feeding: first, the one feeding is the first soul, that is, the vegetative soul. That which is fed is the body containing the soul; and that by which it is fed is food. Thus, a power of the soul is the principle of nourishment as a principal agent, but food is the principle as an instrument.

347. Next, at but since all things (416b23), he defines that first soul, which is called the vegetative soul, which is the soul of plants but only part of an animal’s soul. And about this he does two things.

First, he defines this kind of soul. To understand his definition, we must realize that the three activities of the vegetative soul fall into a certain order.

First is taking food, by which things are maintained in being;

the second and more perfect activity is growth, by which a thing attains a greater completion, both in quantity and in power;

while the third and most complete and ultimate activity is reproduction, by which a being that is already perfect in itself passes on existence and perfection to another being.

For each thing is most complete, as is said in Meteorology 4, when it can make another like itself. (Aristotle, Meteorology 4.1, 380a13–15.) If, then, all things are rightly defined and named from their end, and the end of all the activities of the vegetative soul is to generate another like itself, it follows that we can suitably define this primary soul, that is, the vegetative, as that which is reproductive of another like to itself in species.

348. And in view of his previous remark that this primary soul’s instrument was food, to prevent anyone thinking that it had no other instrument, he shows, at that by which (416b25) that the subject fed has another instrument by which it is fed; as in steering a ship there are two instruments, for the pilot steers with both hand and rudder. (Lect. 8, n. 331.)

Now, the hand is a conjoined instrument of that which has the soul for its form. Whence the rudder is an instrument which moves the boat and itself is moved by the hand, but the hand is not an instrument moved by something exterior, but only by an interior principle; for it is a part of the man moving himself.

Similarly, the instrument of nutrition is twofold. There is the separated instrument not yet informed by the soul; and this is food. But there must also be a conjoined instrument, for the food must be digested, but what effects digestion is something that has heat. As, then, a pilot moves the rudder with his hand, and the boat with the rudder, so the soul moves the food with heat and, by means of the food, nourishes itself. Therefore the heat is a certain conjoined instrument of this soul, in which as a root is found this natural digestive heat; and on account of this, every ensouled being that is nourished has this natural heat, which is a principle of digestion. And it is because this soul is, unlike the intellect, the actuality of a part of the body that it has a conjoined instrument.

349. Summarizing, Aristotle says that he has defined in outline (416b30), that is, in general, what food is; later he will treat of it in its proper accounts. For he wrote a special book on nourishment, as also on the generation of animals and on the movement of animals.