LECTIO EIGHT

             § 324. The Philosopher has just shown that the activities we call vegetative have their origin in the soul. 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'. In the first section he begins by stating the error and then, at 'Nor did he understand' attacks it. Regarding the error itself, we should note that just as Empedocles refused to explain other cases of purposeful arrangement in Nature by any natural finality--for example he said that animals had the sort of feet they have, not in order to help them to walk, but simply because the matter of that part of their bodies happened to be arranged in that sort of way; so also the growth of living things he ascribed merely to the motion of light and heavy bodies. Observing that living things increase their size in different directions, e.g. 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 was due to the earth in their composition, which is heavy and therefore necessarily tends downwards; whilst their upward growth was due to fire which, being light, must tend upwards.

             § 325. Aristotle, then, at 'Nor did he', brings two arguments against this opinion of Empedocles. First, he says that Empedocles misunderstood '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 objects naturally, whilst in others they are merely relative to ourselves. In things which have definite parts as the natural principle of their various movements, these positions are based on Nature itself. Thus the Cosmos as a whole has a mid-point to which heavy things naturally tend, and a circumference to which light things naturally rise; which makes a natural cosmic difference between up and down, according to the natural resting places of the light and the heavy. Again, in living things and mortal beings up and down follow growth and decay: the upper is that part which takes in food, and the lower 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, no part of which is a special source or term of movement, have no natural differences of position in themselves; these are fixed simply by the thing's position relative to us. So is it with inanimate objects: 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 fixed in the same way as in the Cosmos as a whole. It is so in man whose head is turned towards the top of the Cosmos and his feet to its bottom. But the reverse is found in plants, whose roots correspond to the head in man, since they function (as the part which takes in food) in the same way as the head in man. For we reckon that instruments are similar or dissimilar if their functions are so; hence the likeness between a plant's roots and the head of an animal, although they point downwards. Up and down, then, mean opposite things in plants and in the Cosmos as a whole. But brute animals are different; their heads are turned neither up nor down in relation to the Cosmos as a whole. This is what he means when he says that up and down are not for all things (i.e. living things) what they are for the Cosmos.

             § 327. But Empedocles took up and down to be the same for all living things and for the Cosmos. And indeed, if the movement of growth, by which we fix the upper and lower in living beings, followed the movements of the heavy and the light, by which the same relations are fixed 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'. To understand it, we should note that each element in a mixture is present not actually but virtually, and therefore lacking the movement proper to itself. The whole mixture moves with the movement of the element that predominates. If each, as Empedocles seems to have thought, retained its own movement, then, since the elements have natural movements in contrary directions, it follows that they would become quite separate from one another, unless some containing force held them together. Now it is just this container of the element which seems to be the chief cause of growth. For though, to be sure, the increase of the body in its various parts is due to diverse motions of the elements, yet, given the contrariety of elemental motion, growth is inconceivable unless the elements remain conjoined; otherwise there would be division, not growth. But in living things the soul is what holds the elements together; it is also, therefore, the source of their growth.

             § 329. Next, at 'Now it seems to some', he states another theory; which, at 'It is indeed', he then disproves. Unlike the theory of Empedocles, which put the causes of growth and nutrition in both earth and fire, this theory ascribes them only to fire.

             § 330. The reason given is that the cause of anything's modifications or motion would appear to be whatever had such modifications or motions essentially--e.g. fire, being essentially hot, is the cause of heat in things that contain other elements as well; and in the same way earth is the cause of heaviness. 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. But whether fire really feeds itself and grows will be made clear later.

             § 331. Then he attacks the above opinion. But note its grain of truth. All food has to be cooked, and this is done by fire, so that fire does play a part in nutrition, and consequently in growth also; not indeed as the principal agent (which is the soul) but as a secondary, instrumental agent. To say then that fire is a sort of concurrent or instrumental cause of growth and nutrition is true. But it cannot be the principal cause or agent, as he goes on to show.

             § 332. The principal agent in any action is that which imposes the term or natural limit upon what is done; thus in artificial things like boxes or houses the limit or term is fixed, not by the instruments used in the work, but by the art itself. The instruments, as such, are quite 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 man who uses it. Now in Nature each thing obviously has certain limits to its size and its increase; each thing grows to a certain fixed pattern. For as each species of thing requires its own accidental modifications, so it needs its own measure of quantity, though some margin must be left to material differences and other individual factors. Men are not all equal in size. But there is a limit both to their largeness and their littleness; and whatever determines this limit is the true principal cause of growth. But this cannot be fire, because the growth of fire has no naturally fixed limits; it would spread to infinity if an infinite amount of fuel were supplied to it. Clearly, then, fire is not the chief cause of growth and nutrition, but rather the soul. And this is reasonable enough, for the quantitative limits of material things are fixed by form--the specific principle--rather than matter. Now the soul of a living being is to the elements it contains as form is to matter; the soul, then, rather than fire, sets the term and natural limit to size and growth.

416a 19-416b 31

THE VEGETATIVE PRINCIPLE CONTINUED

NUTRITION

             SINCE the vegetative and generative activities of soul are a single power, it is first necessary to fix the nature of nutrition. For it is by this operation that [this power] is distinguished from the others.§ 333

             It would appear that food is a contrary to that which is fed: yet not every contrariety [involves feeding]; but only such contraries as find their increase as well as their origin in each other. For there are many things which originate from opposites: but not all derive their increase thus; (for instance, health coming 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 uncompounded bodies this seems especially to be the case; that which feeds is one thing and that which is fed another.§§ 334-5

             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 opposite,--as though it were impossible that like [should be altered] by like; whilst food is altered and digested. Change in all things is either [to] an opposite or to a mean state. Moreover nutriment is acted upon by that which is nourished: not the latter by the nourishment; any more than a craftsman by his material; but this is acted on by him--the craftsman changing only from repose to activity.§§ 336-8

             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 the [above] theories of food can be upheld: for as it is undigested, one of two contraries is nourished by the other: but in so far as it is digested, one of two similars is nourished by the other. Whence it is clear that both parties speak in one way rightly, and in another way wrongly.§ 339

             Since only what is alive is nourished, what is nourished is the animate body as such. Wherefore nutriment means something related to what is animate, and this not incidentally only.§§ 340-2

             To be nutritive and to be active are two distinct things. In so far as the living being is quantitative, food is active; but in so far as it is substantial, food is nutritive. It preserves the substance, and this just so long as it is fed.§ 343

             And it is productive of generation, not of the one nourished, but of such a one as the one nourished--for this latter is already a substance; and nothing generates itself; it only maintains itself in being.§ 344

             Wherefore, this soul-principle is a power able to preserve what possesses it as a thing of such a kind; and food is preparatory to the operation; hence the being cannot continue, deprived of food.§ 345

             Since there are three factors: what is nourished; that by which it is nourished; and that which nourishes; what nourishes is the primary soul, that which is nourished is the body containing it, and that by which it is nourished is food.§ 346

             Since all things are rightly named from their end and the end [of this soul] is to have generated another being like itself, then the primary soul is generative of what is like itself. 347

              '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 nutriment is: the subject must be further examined later in a special discussion.§§ 348-9