LECTIO THREE

             § 245. Having defined the soul the Philosopher now sets out to prove his definition. First he says what he intends to do, and then, at 'Going back, then,' proceeds to do it. As to the former point, he first determines the method of demonstration that he intends to use; after which, at 'For it is not enough', he explains how certain types of definition can be proved. With regard to the method to be used we should note that, since we can only come to know the unknown if we start from what we know, and since the purpose of demonstration is precisely to cause knowledge, it follows that every demonstration must begin from something more knowable to us than the thing to be made known by it. Now in certain subjects, such as mathematics, which abstract from matter, what is the more knowable is such both in itself and relatively to us; hence in these subjects, demonstration can start from what is absolutely and of its nature more knowable, and therefore can deduce effects from their causes; whence the name given it of a priori demonstration. But in the quite different sphere of the natural sciences, what is more knowable is not the same thing in itself and relatively to us; for sensible effects are generally more evident than their causes. Hence in these sciences we generally have to begin from what is, indeed, absolutely speaking less knowable, but is more evident relatively to us (see the Physics, Book I).

             § 246. And this is the kind of demonstration which will be used here. So he says that what is of its nature more certain, and is more evident to thought, becomes certain to us by means of things less certain in nature but more certain to us; and that this shows us the method to use in enquiring once more into the soul and showing the grounds of the definition given above.

             § 247. Then, at 'For it is not enough', he tells us why the question must be taken up again. Certain definitions can, he says, be demonstrated, and in these cases it is not enough for the defining formula to express, as most 'formulae', i.e. definitions, do, the mere fact; it should also give the cause of the fact; and this being given, one can then proceed to deduce the definition which states the mere fact. At present many definitions are given in the form of conclusions; and he gives an example from geometry.

             § 248. To understand which we must note that there are two kinds of four-sided figure: those whose angles are all right angles, and these are called rectangles; and the kind with no right angles, and these are called rhomboids. Of the rectangles, again, there is one with four equal sides--the square or tetragon; and another which, without having all four sides equal, has two pairs of equal and opposite sides--the oblong. Thus:

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—            — 

—            —

—            —   square

—            —

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—                   —      oblong

—                   —

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 \                   \

   \                   \    rhomboid

     \                   \

       --------------------

             § 249. Note further, that in any rectangular surface the two straight lines enclosing the right angle are said to contain the whole figure; because, the other two sides being equal to these two, each equal to its opposite, it follows that one of the enclosing lines measures the length of the whole figure, and the other its breadth: so that the whole figure is given in the contact of the two lines. If we imagine one of these lines moving along the other we see the whole figure form itself.

             § 250. Note also that if, between the two unequal sides that contain the oblong, one takes the proportional mean and squares it, one gets a quadrilateral equal to the oblong. This would take too long to prove geometrically, so let a numerical argument do for the present. Let our oblong then have its longer side 9 feet and its shorter side 4 feet. Then the proportional mean line will be 6 feet; for as 6 is to 9, so 4 is to 6. Now the square of this line must equal the oblong; which is obvious numerically: 4X9=36, 6X6=36.

             § 251. Now it is thus, he says, that the question, What is a square (i.e. the quadrilateral equal to an oblong)? is answered; it is said 'to be an orthogon', i.e. a right-angled plane figure, which is 'equilateral', i.e. having all its sides equal, and so on. 'Such a term', i.e. a definition of this sort, is really 'of the nature of a conclusion', namely of a presupposed demonstration; whereas if one were to say that a square is 'the discovery of a mean line', i.e. of the proportional mean between the two unequal sides of the oblong, meaning that a square is what is constructed from this line, then at last the definition would disclose the 'reason why' of the thing defined.

             § 252. Note, however, that this example is only relevant to the definition of the soul in so far as this definition is simply to be demonstrated; it must not be taken to imply that our demonstration can proceed a priori from causes to effects.

             § 253. Next, at 'Going back then', he begins to prove the definition of the soul given above; and this in the way indicated, i.e. from effects to causes. This is how he sets about it: the first principle of life in things is the actuality and form of living bodies; but soul is the first principle of life in living things; therefore it is actuality and form of living bodies. Now this argument is clearly a posteriori; for in reality the soul is the source of vital activities because it is the form of a living body, not e converso. So he has to do two things here; first, to show that soul is the source or principle of vitality, and secondly, to show that the first principle of vitality is the form of living bodies (this comes at 'Since that whereby etc.'). With regard to the first point he does three things: (a) he distinguishes modes of life, (b) he shows that the soul is the principle of living activities--at 'Hence all plants'; and (c) he explains how these parts of the soul are interrelated, by means of which it originates vital activities. This is at 'We now ask whether each of these'.

             § 254. He starts then by saying that to carry out our intention of proving the definition of the soul, we must assume as a kind of principle that things with souls differ from those without souls in being alive. Life is the test; and as life shows itself in several ways, if a thing has life in only one of these ways it is still said to be alive and to possess a soul.

             § 255. Life, he says, shows itself in four modes: (1) as intellectual; (2) as sensitive; (3) as the cause of motion or rest in space; (4) as cause of the motions of taking nourishment, decay and growth. He distinguishes only these four modes, although he has already distinguished five main types of vital activity, and this because he is thinking here and now of the degrees of animate being. There are four such degrees, distinguished in the same way as the four modes in which life is manifested: for some living things, i.e. plants, only take nourishment and grow and decay; some have also sensation, but are always fixed to one place--such are the inferior animals like shell-fish; some again, i.e. the complete animals like oxen and horses, have, along with sensation, the power to move from place to place; and finally some, i.e. men, have, in addition, mind. The appetitive power, which makes a fifth type of vitality, does not, however, imply a distinct degree of living being; for it always accompanies sensation.

             § 256. Next, at 'Hence all plants', he shows that a soul is involved in all these modes of life. He does this with regard (1) to plants, and (2) to animals, at 'But an animal is such, primarily'. Then (3), he summarises, at 'For what cause', what has been said and remains to be said. As to (1) he does two things. First he shows that the life-principle in plants is a soul. We have remarked, he says, that whatever evinces one of the four modes of life mentioned above can be said to live. Therefore plants are alive; for they all possess some intrinsic power or principle of growth and decay.

             § 257. Now this principle is not mere nature. Nature does not move in opposite directions, but growth and decay are in opposite directions; for all plants grow not only upwards or downwards, but in both directions. Hence a soul, not nature, is clearly at work in them. Nor do plants live only when actually growing or decaying, but, as things that take nourishment, they live so long as they can assimilate the food that induces growth.

             § 258. Next, at 'It is possible', he shows that this principle of feeding and growing can exist apart from other life-principles, but these cannot exist apart from it, at least in things subject to death. He adds this last clause because of immortal beings like immaterial substances or heavenly bodies; because, if these have a soul, it is intellectual; it is not a capacity to take nourishment. And the separability of this life principle from others is clearly evident in plants which have, in fact, no other one but this. It follows that what first of all causes life in mortal things is this principle of growth and nourishment, the so-called vegetative soul.

             § 259. Then, at 'But an animal is such primarily', he shows that a soul is the source of living in animals. And here he does two things. First he observes that what primarily distinguishes animals is sensation, though there are animals which have local movement as well; for we call those things animals (not just living beings) which have sensation, even if they are fixed to one place. For there are many such animals whose nature restricts them to one place, but which have the power of sense, e.g. shell-fish, which cannot move from place to place.

             § 260. Then at 'Touch is', he shows that touch is the primary sense in animals. For just as the vegetative soul, he says, is separable from all the senses including touch, so touch is separable from all the other senses. For many inferior animals have only the sense of touch; but there are no animals without this sense. Now that degree of soul in which even plants participate we call the vegetative. Hence we can distinguish three degrees of living beings: first, plants; secondly, the inferior animals fixed to one place and with no sense but touch; and, thirdly, the higher, complete animals which have the other senses and also the power to move from place to place. And a fourth degree consists, evidently, of beings which have all this and mind as well.

             § 261. Finally, at 'For what cause', summarising what has been said and remains to be said, he remarks that the cause of both these phenomena, namely the separability of the vegetative principle from sensation and of touch from the other senses, will be given later on. He does this at the end of the whole Treatise. For the present it suffices to say that 'soul' is the one principle underlying the four distinct modes in which life is manifested, namely the vegetative mode which belongs to plants and to all living things; the sensitive mode in all animals; the intellectual mode in all men; and fourthly, the mode that is a power to move from place to place, which exists in all the higher animals, both those with senses only and those with intellect as well.

413b 13-414a 28

DIFFERENT KINDS OF SOUL

             WE now ask whether each of these [powers] is a soul, or a part of a soul: and if a part, whether it is separable only in thought or has also a distinct place.§ 262

             Concerning some of these powers it is not difficult to see [the answers to our questions]; others, however, give rise to doubts. For, as in the case of plants some, on being divided, seem to go on living in separation from one another, as if there were in each plant one soul in act, but several in potency; so we find it happens in the case of other differentiations of soul, for instance in divided animals each division has sensation and local motion; and if sensation, phantasm and appetition; for where there is sensation there is pleasure, and pain, and where these are there must necessarily be appetition.§§ 263-7

             But as regards intellect and the speculative faculty, nothing has so far been demonstrated; but it would seem to be another kind of soul, and alone capable of being separated, as the eternal from the perishable. It is evident, however, from the foregoing, that the other parts of the soul are not separable, as some have said.§ 268

             By definition, however, they are obviously distinct. For if feeling is other than opining, the sense-faculty will differ from the capacity to form opinions. Likewise with each of the other powers mentioned.§ 269

             Further, all these powers are in some animals; in others, some only; in yet others, only one. This makes the varieties of animal. Why this should be so will be considered later. The same obtains with regard to the senses: certain species of animal have all; certain others, some; yet others have only the one most necessary, touch.§ 270

             Since 'that whereby we live and perceive' can mean two things,--like 'that by which we know', for we name one thing knowledge, and another, the soul, though we are said to know by both of these; and likewise as 'that by which we are healthy'; for health is one thing, while a part of the body (or the whole of it) is another; and in these cases knowledge, or health, is the form and specific essence or ratio, and, as it were, the act of such as can receive knowledge in the one case and health in the other (for the action of an agent seems to exist in the recipient or disposed material)--and soul being that by which we primarily live and perceive and move and understand, it follows that the soul will be a sort of species or ratio; not, as it were, a matter or substratum. Substance is predicated in three ways, as we have said: in one way as the form; in another as the matter; and in another as what is from both. Of these, matter is the potency, form the act; hence if what is from both is the animate being, the body is not the act of the soul, but the soul of the body.§§ 271-5.

             And on this account they were right who thought that the soul is neither apart from the body nor the same as the body; for it is not, indeed, the body; yet is something of the body. And therefore it is in a body, and a body of a definite kind; and not as some earlier thinkers made out, who related it to a body without defining at all the nature and quality of that body; despite the fact that it is apparent that not any subject whatever can receive any form at random. And that such is the case is confirmed by reason: the act of any one thing is of that which is in potency to it, and it occurs naturally and fittingly in matter appropriate to it.

             That the soul, then, is an actuality and formal principle of a thing in potency to exist accordingly, is evident from these considerations.§§ 276-8