Book I, Chapter 1

Holding as we do that knowledge is among the things that are noble and honourable, and that one kind of knowledge is more so than another, either in virtue of its exactness or because it is of better and more wonderful objects, on both these grounds we should reasonably rank the inquiry concerning the soul among the first. And the knowledge of it seems to contribute greatly to truth as a whole, and above all to the study of nature; for the soul is, as it were, the principle of animals. We seek to observe and to come to know both its nature and its essence, and then all that belongs to it as attributes; of these, some seem to be affections proper to the soul, while others seem to belong to animals as well by reason of the soul.

But in every way and in every respect it is one of the hardest of things to attain any conviction about the soul. For since the inquiry — I mean the inquiry into the essence and into what a thing is — is one that is common to many other subjects, it might perhaps seem to someone that there is a single method for all the things whose essence we wish to know, just as there is demonstration for the attributes that belong to them incidentally; so that we should have to look for this method. But if there is no single and common method for finding what a thing is, our task becomes still harder; for we shall have to grasp, in each case, what the way is. And even if it should be evident whether it is a demonstration of some kind, or division, or yet some other method, there are still many difficulties and much room for going astray as to the things from which our inquiry ought to start; for the principles of different subjects are different, as with numbers and planes.

First, perhaps, it is necessary to determine in which of the genera the soul falls and what it is — I mean whether it is a this-something and a substance, or a quality, or a quantity, or some other of the categories that have been distinguished; and further, whether it belongs among the things that are potentially, or is rather a kind of actuality (entelecheia); for this makes no small difference. We must also consider whether it is divisible into parts or without parts, and whether all soul is of the same kind or not; and if it is not of the same kind, whether souls differ in species or in genus. For at present those who speak and inquire about the soul seem to look only into the human soul.

But we must take care not to let it escape us whether the account of soul is one, as the account of animal is, or whether there is a different one for each — for horse, dog, man, god — while "animal", the universal, is either nothing at all or is posterior; and the same holds if any other common term should be predicated. Again, if there are not many souls but parts of one soul, there is the question whether we ought to inquire into the whole soul first or into the parts. And it is hard to determine, among these parts as well, which are by nature different from one another, and whether we ought to inquire into the parts before their functions, or the functions first — thinking or the intellect, perceiving or the perceptive faculty — and likewise in the other cases. But if the functions come first, one might again raise the difficulty whether the objects that correspond to them ought to be investigated before them: the object of perception before the perceptive faculty, and the object of thought before the thinking faculty.

It seems that not only is it useful to know what a thing is in order to discern the causes of the attributes of substances — as in mathematics it is useful to know what the straight and the curved are, or what a line and a plane are, in order to see to how many right angles the angles of a triangle are equal — but conversely the attributes contribute a great part towards knowing what a thing is. For when we are able to give an account, in accordance with how they appear, of the attributes, either of all of them or of most, then we shall also be in the best position to speak about the essence. For the starting-point of every demonstration is what a thing is; hence it is clear that all those definitions which do not enable us to come to know the attributes, nor even to make an easy conjecture about them, have been stated in a merely dialectical and empty way.

The affections of the soul also present a difficulty: are they all shared with that which has the soul, or is there something proper to the soul itself? For this must be grasped, and yet it is not easy. In most cases it appears that the soul neither undergoes nor does anything without the body — as in growing angry, being confident, desiring, and perceiving in general. Thinking seems most of all to be proper to the soul; but if this too is a kind of imagination, or does not occur without imagination, then not even this could be without a body.

If, then, there is some function or affection of the soul that is proper to it, it would be possible for the soul to be separated; but if there is nothing proper to it, it will not be separable. It will be like the straight line, which, qua straight, has many attributes — for instance, it touches a bronze sphere at a point — though the straight line will not touch it if it is separated; for it is inseparable, since it is always found together with some body.

It seems that all the affections of the soul, too, involve a body: spirit, gentleness, fear, pity, confidence, and again joy, loving and hating; for along with all these the body undergoes something. An indication of this is that sometimes, when strong and vivid affections occur, a man is not provoked or frightened at all, whereas at other times he is moved by small and faint ones, whenever the body is already stirred up and is in the condition it is in when a man is angry. And here is something that makes it still clearer: men come to be in the affections of one who is afraid even when nothing frightening is happening. And if this is so, it is clear that the affections are accounts embodied in matter. Hence their definitions will be of this sort: to be angry is a certain movement of such-and-such a body, or of a part or faculty of it, brought about by this for the sake of that. And for these reasons it already belongs to the student of nature to study the soul — either all soul, or soul of this kind.

The student of nature and the dialectician would define each of these affections differently — for instance, what anger is: the one would call it a desire to return pain for pain, or something of that sort, the other a boiling of the blood and of the hot stuff about the heart. Of these, the one gives the matter, the other the form and the account. For the account is the form of the thing, and this form must be in such-and-such matter if the thing is to exist; just as, with a house, the account is of this sort — that it is a shelter which prevents destruction by winds and rains and heats — while another will say that it is stones and bricks and timbers, and a third that it is the form in these materials, for the sake of these ends.

Which, then, of these is the student of nature? Is it the one who is concerned with the matter and ignorant of the account, or the one concerned with the account alone? Or is it rather the one who is concerned with what comes from both? And what, then, is each of the other two? Or is there in fact no one who deals with the affections of matter that are not separable, taken as not separable? Rather, the student of nature is concerned with all the functions and affections of such-and-such a body and such-and-such matter; while whatever is not of this kind belongs to another, and in some cases to a craftsman, if it so happens — a carpenter, say, or a physician. As for the things that are not separable, but are considered not as affections of such a body and are taken in abstraction, they belong to the mathematician; and as considered separated, to the first philosopher.

But we must return to the point from which the discussion set out. We were saying that the affections of the soul are inseparable from the natural matter of animals, in the way in which such affections as spirit and fear belong to them, and not in the way that a line and a plane are inseparable.