De Anima

So much for the theories of soul handed down by our predecessors. Let us, then, make a fresh start and try to determine what soul is and what will be its most comprehensive definition. Now there is one class of existent things which we call substance, including under the term, firstly, matter, which in itself is not this or that; secondly, shape or form, in virtue of which the term this or that is at once applied; thirdly, the whole made up of matter and form. Matter is identical with potentiality, form with actuality. And there are two meanings of actuality: knowledge illustrates the one, exercise of knowledge the other. Now bodies above all things are held to be substances, particularly such bodies as are the work of nature; for to these all the rest owe their origin. Of natural bodies some possess life and some do not: where by life we mean the power of self-nourishment and of independent growth and decay. Consequently every natural body possessed of life must be substance, and substance of the composite order. And since in fact we have here body with a certain attribute, namely, the possession of life, the body will not be the soul: for the body is not an attribute of a subject, it stands rather for a subject of attributes, that is, matter. It must follow, then, that soul is substance in the sense that it is the form of a natural body having in it the capacity of life. Such substance is actuality. The soul,

therefore, is the actuality of the body above described. But the term "actuality" is used in two senses; in the one it answers to knowledge, in the other to the exercise of knowledge. Clearly in this case it is analogous to knowledge: for sleep, as well as waking, implies the presence of soul; and, whilst waking is analogous to the exercise of knowledge, sleep is analogous to the possession of knowledge without its exercise; and in the same individual the possession of knowledge comes in order of time before its exercise. Hence soul is the first actuality of a natural body having in it the capacity of life. And a body which is possessed of organs answers to this description.—We may note that the parts of plants, as well as those of animals, are organs, though of a very simple sort: for instance, a leaf is the sheath of the pod and the pod of the fruit. The roots, again, are analogous to the mouths of animals, both serving to take in nourishment. If, then, we have to make a general statement touching soul in all its forms, the soul will be the first actuality of a natural body furnished with organs. Hence there is no need to enquire whether soul and body are one, any more than whether the wax and the imprint are one; or, in general, whether the matter of a thing is the same with that of which it is the matter. For, of all the various meanings borne by the terms unity and being, actuality is the meaning which belongs to them by the fullest right.

It has now been stated in general terms what soul is, namely, substance as notion or form. And this is the quiddity of such and such a body. Suppose, for example, that any instrument, say, an axe, were a natural body, its actuality would be its substance, would in fact be its soul. If this were taken away, it would cease, except in an equivocal sense, to be an axe. But the axe is after all an axe. For it is not of a body of this kind that the soul is the quiddity, that is, the notion or form, but of a natural body of a particular sort, having in itself the origination of motion and rest.

Further, we must view our statement in the light of the parts of the body. For, if the eye were an animal, eyesight would be its soul, this being the substance as notion or form of the eye. The eye is the matter of eyesight, and in default of eyesight it is no longer an eye, except equivocally,

like an eye in stone or in a picture. What has been said of the part must be understood to apply to the whole living body; for, as the sensation of a part of the body is to that part, so is sensation as -a whole to the whole sentient body as such. By that which has in it the capacity of life is meant not the body which has lost its soul, but that which possesses it. Now the seed in animals, like the fruit in plants, is that which is potentially such and such a body. As, then, the cutting of the axe or the seeing of the eye is full actuality, so, too, is the waking state; while the soul is actuality in the same sense as eyesight and the capacity of the instrument. The body, on the other hand, is simply that which is potentially existent. But, just as in the one case the eye means the pupil in conjunction with the eyesight, so in the other soul and body together constitute the animal.

Now it needs no proof that the soul—or if it is divisible into parts, certain of its parts—cannot be separated from the body, for there are cases where the actuality belongs to the parts themselves. There is, however, no reason why some parts should not be separated, if they are not the actualities of any body whatever. Again, it is not clear whether the soul may not be the actuality of the body as the sailor is of the ship. This, then, may suffice for an outline or provisional sketch of soul.

But, as it is from the things which are naturally obscure, though more easily recognised by us, that we proceed to what is clear and, in the order of thought, more knowable, we must employ this method in trying to give a fresh account of soul. For it is not enough that the defining statement should set forth the fact, as most definitions do; it should also contain and present the cause: whereas in practice what is stated in the definition is usually no more than a conclusion. For example, what is quadrature? The construction of an equilateral rectangle equal in area to a given oblong. But such a definition expresses merely the conclusion. Whereas, if you say that quadrature is the discovery of a mean proportional, then you state the reason.

We take, then, as our starting-point for discussion that it is life which distinguishes the animate from the inanimate. But the term life is used in various senses; and, if life is present in but a

single one of these senses, we speak of a thing as living. Thus there is intellect, sensation, motion from place to place, the motion concerned with nutrition and, further, decay and growth. Hence it is that all plants are supposed to have life. For apparently they have within themselves a faculty and principle whereby they grow and decay in opposite directions. For plants do not grow upwards without growing downwards; they grow in both directions equally, in fact in all directions, as many as are constantly nourished and therefore continue to live, so long as they are capable of absorbing nutriment. This form of life can be separated from the others, though in mortal creatures the others cannot be separated from it. In the case of plants the fact is manifest: for they have no other faculty of soul at all.

It is, then, in virtue of this principle that all living things live, Sensation Wether animals or plants. But it is sensation primarily which constitutes the animal. For, provided they have sensation, even those creatures which are devoid of movement and do not change their place are called animals and are not merely said to be alive. Now the primary sense in all animals is touch. But, as the nutritive faculty may exist without touch or any form of sensation, so also touch may exist apart from the other senses. By nutritive faculty we mean the part of the soul in which even plants share. Animals, however, are found universally to have the sense of touch: why this is so in each of the two cases will be stated hereafter.

For the present it may suffice to say that the soul is the origin of the functions above enumerated and is determined by them, namely, by capacities of nutrition, sensation, thought, and by motion. But whether each one of these is a soul or part connection of a soul and, if a part, whether it is only logically functions. distinct or separable in space also is a question, the answer to which is in some cases not hard to see: other cases present difficulties. For, just as in the case of plants some of them are found to live when divided and separated from each other (which implies that the soul in each plant, though actually one, is potentially several souls), so, too, when insects or annelida are cut up, we see the same thing happen with other varieties of soul: I mean, each of the segments has sensation and moves from place

to place, and, if it has sensation, it has also imagination and appetency. For, where there is sensation, there is also pleasure and pain: and, where these are, desire also must of necessity be present. But as regards intellect and the speculative faculty the case is not yet clear. It would seem, however, to be a distinct species of soul, and it alone is capable of separation from the body, as that which is eternal from that which is perishable. The remaining parts of the soul are, as the foregoing consideration shows, not separable in the way that some allege them to be: at the same time it is clear that they are logically distinct. For the faculties of sensation and of opinion taken in the abstract are distinct, since to have sensation and to Opine are distinct. And so it is likewise with each of the other faculties above mentioned. Again, while some animals possess all these functions, others have only some of them, others only one. It is this which will differentiate animal from animal. The reason why this is so must be investigated hereafter. The case is similar with the several senses: some animals have all of them, others some of them, others again only one, the most indispensable, that is, touch.

Now"that by which we live and have sensation" is a phrase with two meanings, answering to the two meanings of "that by which we know" (the latter phrase means, firstly, knowledge and, secondly, soul, by either of which we say we know). Similarly that by which we have health means either health itself or a certain part, if not the whole, of the body. Now of these knowledge and health are the shape and in some sort form, the notion and virtual activity, of that which is capable of receiving in the one case knowledge, in the other health: that is to say, it is in that which is acted upon or conditioned that the activity of the causal agencies would seem to take effect. Now the soul is that whereby primarily we live, perceive, and have understanding: therefore it will be a species of

notion or form, not matter or substratum. Of the three meanings of substance mentioned above, form, matter and the whole made up of these two, matter is potentiality and form is actuality. And, since the whole made up of the two is endowed with soul, the body is not the actuality of soul, but soul the actuality of a particular body. Hence those are right who regard the soul as not independent of body and yet at the same time as not itself a species of body. It is not body, but something belonging to body, and therefore resides in body and, what is more, in such and such a body. Our predecessors were wrong in endeavouring to fit the soul into a body without further determination of the nature and qualities of that body: although we do not even find that of any two things taken at random the one will admit the other. And this result is what we might expect. For the actuality of each thing comes naturally to be developed in the potentiality of each thing: in other words, in the appropriate matter. From these considerations, then, it is manifest that soul is a certain actuality, a notion or form, of that which has the capacity to be endowed with soul.

Of the powers of soul above mentioned, namely, those of nutrition, appetency, sensation, locomotion and understanding, some living things, as we remarked, possess all, others some, others again only one. Plants possess the nutritive faculty only: other things along with this have Appetency sensation; and, if sensation, then also appetency: where under appetency we include desire, anger and wish. But:" all animals have at least one sense, touch: and, where sensation is found, there is pleasure and pain, and that which causes pleasure and pain; and, where these are, there also is desire, desire being appetite for what is pleasurable. Again, they have a sensation concerned with nutriment, touch being such a sense. For it is by what is dry and moist, hot and cold, that all living things are nourished (and these qualities are perceived by touch, whereas the other sensibles are not, except incidentally): for sound, colour and odour contribute nothing to nutriment, while flavour

is one of the tangible objects. Hunger again, and thirst are forms of desire, the one for what is hot or dry, the other for what is cold or moist. Flavour is, as it were, the seasoning of these. We will deal with these in detail hereafter: at present let it suffice to say that all animals which have the sense of touch are also endowed with appetency. Whether they have imagination is not clear: this, too, must be considered later. Some have in addition the power of locomotion. Others—that is to say, man and any other species like man or, possibly, superior to him—have also the thinking faculty and intellect.

From this it is clear that there is one definition of soul exactly as there is one definition of figure: for there is in the of soul, os one case no figure excepting triangle, quadrilateral and the rest,.nor is there in the other any species of soul apart from those above mentioned. Again, a definition might be constructed which should apply to all figures, but not specially to any species of figure. And similarly with the species of soul above enumerated. Hence it would be absurd here as elsewhere to seek a general definition which will not be properly a definition of anything in existence and will not be applicable to the particular irreducible species before us, to the neglect of the definition which is so applicable.

The types of soul resemble the series of figures. For, alike in figures and in things animate, the earlier form exists potentially in the later, as, for instance, the triangle potentially in the quadrilateral, and the nutritive faculty in that which has sensation. So that we must examine in each case separately, what is the soul of plant, of man or of beast. Why they are related in this order of succession remains to be considered. There is no sensitive faculty apart from the nutritive: and yet the latter exists without the former in plants. Again, none of the other senses is found apart from touch; while touch is found apart from the others, many animals having neither sight nor hearing nor sense of smell. Also of those which possess sensation, some can move from place to place, others cannot.

Lastly and most rarely, they have the reasoning faculty and thought. For those perishable creatures which possess reason are endowed with all the other species of soul, but not all those which possess each of the other faculties have reason. Indeed, some of them have not even imagination, while others live by imagination alone. As for the speculative intellect, it calls for a separate discussion. Meanwhile it is clear that an account of the several faculties is at the same time the most appropriate account of soul.

The enquirer who approaches this subject must ascertain what each of these faculties is before he proceeds to investigate procedure. the questions next in order and so forth. But if we are asked to state what each of these is; that is to say, what the cognitive, sensitive and nutritive faculties respectively are, we must begin by stating what the act of thinking is and what the act of sensation is. For activities and functions are logically prior to faculties. But, if so, and if a study of the correlative objects should have preceded, these objects will for the same reason have to be defined first: I mean, nutriment and the sensible and intelligible. Consequently we have first to treat of nutriment and of generation.

The nutritive soul belongs to other living things as well as man, being the first and most widely distributed faculty, in virtue of which all things possess life. Its functions are reproduction and assimilation of nutriment. For it is the most natural function in all living things, if perfect and not defective or spontaneously generated, to reproduce their species; animal producing animal and plant plant, in order that they may, so far as they can, share in the eternal and the divine. For it is that which all things yearn after, and that is the final cause of all their natural activity. Here final cause is an ambiguous term, which denotes either the purpose for which, or the person for whom, a thing is done. Since, then, individual things are incapable of sharing continuously in the eternal and the divine, because nothing in the world of perishables can abide numerically one and the same, they partake in the eternal and

divine, each in the only way it can, some more, some less. That is to say, each persists, though not in itself, yet in a representative which is specifically, not numerically, one with it.

Now the soul is cause and origin of the living body. But cause and origin are terms used in various senses: accordingly soul is cause in the three senses of the word cause already determined. For the soul is the cause of animate bodies as being in itself the origin of motion, as final cause and as substance. Clearly it is so as substance, substance being the cause of all existence. And for living things existence means life, and it is the soul which is the cause and origin of life. Furthermore, actuality is the notion or form of that which has potential existence. Manifestly, too, the soul is final cause. For nature, like intelligence, acts for a purpose, and this purpose is for it an end. Such an end the soul is in animals, and this in the order of nature, for all the natural bodies are instruments of soul: and this is as true of the bodies of plants as of those of animals, shewing that all are means to the soul as end; where end has two senses, the purpose for which and the person for whom. Moreover, the soul is also the origin of motion from place to place, but not all living things have this power of locomotion. Qualitative change, also, and growth are due to soul. For sensation is supposed to bea sort of qualitative change, and nothing devoid of soul has sensation. The same holds of growth and decay. For nothing undergoes natural decay or growth except it be nourished, and nothing is nourished unless it shares in life.

Empedocles is mistaken in adding that in plants, in so far as they strike their roots downwards, growth takes place because the earth in them has a natural tendency in this direction and that, when they shoot upwards, it is because the fire in them has a similar tendency upwards. He is wrong in his view of up and down. For up and down are not the same for all individuals as for the universe. On the contrary, the roots of plants correspond to the heads of animals, if we are to

make identity and diversity of organs depend upon their functions. Besides, what is it that holds together the fire and the earth, tending, as they do, in opposite directions? For they will be rent asunder, unless there is something to prevent it: while, if there is, it is this which is the soul and the cause of growth and nourishment.

Some hold the nature of fire to be singly and solely the cause of nourishment and growth. For it would seem that fire is the only body or element which of itself is nourished and grows. Hence fire might be supposed to be the operative cause, both in plants and animals. Whereas, though it is in a sense a joint cause, it is not a cause absolutely: it is rather the soul which is so. For fire goes on growing to infinity, as long as there is fuel to be consumed, but in natural wholes there is always a limit or proportion which determines growth and size. But this belongs to the soul and not to fire, to form rather than' to matter.

The nutritive faculty of the soul being the same as the reproductive, it is necessary first to give a definition of nutriment. For it is by the nutritive function that this faculty is separated off from the others. The common view is that contrary is nutriment to contrary; though not in every case, but wherever each of two contraries is not only generated by, but derives growth from, the other. For many things are derived from one another, but not all of them are quantities: thus the sick man becomes well. But it is found that even the contraries supposed to derive growth from each other are not fed by one another in the same way: while water serves to feed fire, fire is not nutriment to water. It would seem, then, that it is in the simple bodies above all that of two contraries one is nutriment and the other is nourished. Yet here is a difficulty. It is said by the one side that like is nourished by, as well as derives its growth from, like; while the others, again, as we explained, hold that contrary is nourished by contrary, on the ground that like cannot be affected by like, while food undergoes change and is digested. Now change is always in the direction of the opposite, or of the intermediate state. Further, nutriment is acted upon by that which it nourishes, and not the latter by the former: just as

the carpenter is not affected by his material, but on the contrary the material by the carpenter. The carpenter merely passes to activity from inaction. But it makes a difference whether by nutriment we mean the final, or the primary, form of what is added. If both are nutriment, the one as undigested, the other as digested, it will be possible to use the term nutriment in conformity with both theories. For, in so far as it is undigested, contrary is nourished by contrary: and, in so far as it is digested, like by like. So that clearly both sides are in a manner partly right and partly wrong. But, since nothing is nourished unless it possesses life, that which is nourished must be the animate body as such: so that nutriment also is relative to the animate being which it nourishes: and this not incidentally merely.

There is, however, a difference between nutritivity and conducivity to growth. In so far as the animate thing is quantitative, what is taken promotes growth; in so far as it is a definite individual, what is taken nourishes. For the animate thing preserves its substance or essential nature and exists as long as it is nourished: and it causes the production, not of that which is nourished, but of another individual like it. Its essential nature already exists, and nothing generates itself, it only maintains its existence. Hence the above described principle of the soul is the power to preserve in existence that which possesses it in so far as it is a definite individual, while nutrition prepares it for activity. Therefore it cannot live when deprived of nutriment. There are, then, these three things, that which is nourished, that with which it is nourished, and that which nourishes it. The last of the three is the primary soul, that which is nourished is the body which contains the soul, that wherewith it is nourished is nutriment. As, however, it is right to name all things from the end they subserve, and the end here is reproduction of the species, the primary soul is that which is capable of reproducing the species. That with which the living thing is nourished may be understood in two senses, just as that with which one steers may mean the hand or the rudder; the former, the hand, both causing motion and being moved, the latter, the rudder, being simply moved. Now it is necessary that all food should be capable of digestion, and digestion is promoted by heat; this explains why every animate thing has warmth. This, then, is an outline of what nutriment is. It must be more clearly defined hereafter in the discussion devoted specially to it.

Now that these points have been determined, let us proceed to a general discussion of all sensation. As above remarked, sensation consists in being moved and acted upon, for it is held to be a species of qualitative change. Some add that like is in fact acted upon by like. How far this is possible or impossible we have explained in the general discussion of action and passivity. The question arises why there is no sensation of the senses themselves: that is, why they produce no sensation apart from external sensibles, though the senses contain fire, earth and the other elements, which are the objects of sensation either in themselves or through their attributes. Evidently it Sensation follows that the faculty of sensible perception exists not in activity, but only in potentiality. Hence it must be here as with the fuel which does not burn of and in itself without something to make it burn; otherwise it would kindle itself and would have no need of the fire which is actually existent. Now to have sensation has two meanings: we use the terms hearing and seeing "of that which has the capacity to hear and see, even though it be at the time asleep, just as we do of that which already actually hears and sees. And therefore sensation, too, will have two meanings: it may mean either potential or actual sensation. Similarly with having sensation, whether potential or actual.

Let us then first proceed on the assumption that to be acted Agent ana Upon or moved is identical with active operation. For movement is in fact active operation of some sort, though incomplete, as we have elsewhere explained. But in every case things are acted upon and moved by an agent in actual operation. It follows that in one sense what is acted upon is acted upon by what is like it, in another sense by what is unlike it, as we have explained. That is to say, while being acted upon it is unlike, after it has been acted upon it is like the agent.

We must also draw a distinction in regard to the terms potentiality and actuality: at present we are using them without qualification. For instance, we may use the term wise, firstly, in the sense in which we might speak of man as wise, because man is one of the genus of beings which are wise and have wisdom; secondly, in the sense in which we at once call the man wise who has learnt, say, grammar. Now of these two men each possesses the capacity, but in a different sense: the one because the genus to which he belongs, that is to say, his matter, is potentially wise; the other because he is capable, if he chose, of applying the wisdom he has acquired, provided there is nothing external to hinder. Whereas he who is at the moment exercising his wisdom is in actuality and is wise in the proper sense of the term: for example, he knows the A before him. Thus the first two are both potentially wise: the first becomes wise actually after he has undergone qualitative change through instruction and often after transition from the reverse condition; while in the latter case it is by another kind of transition that the man passes from the mere possession, without the use, of sensation or grammar to the use of it.

To suffer or be acted upon, too, is a term of more than one meaning. Sometimes it means a sort of destruction by the contrary, sometimes it is rather a preservation of what is potentially existent by what is actually existent and like it, so far as likeness holds of potentiality when compared with actuality. For it is by exercise of knowledge that the possessor of knowledge becomes such in actuality: and this either is no qualitative change (for the thing develops into its own nature and actuality), or else is qualitative change of a different sort. Hence it is not right to say that that which thinks undergoes change when it thinks, any more than that the builder undergoes change when he builds. That, then, which works the change from potential existence to actuality in a thinking and intelligent being should properly receive a different name and not be called instruction: while that which learns and is brought from potential to actual knowledge by that which is in actuality and capable of instructing should either not be said to suffer or be acted upon at

all, or else two modes of change should be assumed, one to the negative states and the other to the normal habits and the true nature.

In the sensitive subject the first change is due to the parent: once generated it possesses sensation exactly in the same sense as we possess knowledge. And to have actual sensation corresponds to exercise of knowledge. There is this difference, however, that in the one case the causes of the activity are external: as, for instance, the objects of sight, hearing and the other senses. The reason is that actual sensation is always of particulars, while knowledge is of universals: and these universals are, in a manner, in the soul itself. Hence it is in our power to think whenever we please, but sensation is not in our power: for the presence of the sensible object is necessary. It is much the same with the sciences which deal with sensible objects; and for the same reason, namely, that sensibles are particulars and are external.

But we shall have a further opportunity of making this clear hereafter. For the present let us be content to have established that of the two meanings of potentiality, the one according to which a child might be called potentially a general, and the other according to which a man of full age might be so called, it is the latter which applies to the faculty of sense-perception. But as this distinction has no word to mark it, although the fact and the nature of the distinction have been established, we are compelled to use the terms to suffer or be acted upon and to be qualitatively changed as if they were the proper terms. Now, as has been explained, the sensitive faculty is potentially such as the sensible object is in actuality. While it is being acted upon, it is not yet similar, but, when once it has been acted upon, it is assimilated and has the same character as the sensible object.

In considering each separate sense we must first treat of their objects. By the sensible object may be meant any one of three things, two of which we say are perceived in themselves or directly, while the third is perceived per accidens or indirectly. Of the first two the one is the special object of a particular sense, the other an object common to all the senses. By a special object of a particular sense I mean that which cannot be perceived by any other sense and in respect to which deception is impossible; for

example, sight is of colour, hearing of sound and taste of flavour, while touch no doubt has for its object several varieties. But at any rate each single sense judges of its proper objects and is not deceived as to the fact that there is a colour or a sound; though as to what or where the coloured object is or what or where the object is which produces the sound, mistake is possible. Such then, are the special objects of the several senses. By common sensibles are meant motion, rest, number, figure, size: for such qualities are not the special objects of any single sense, but are common to all. For example, a particular motion can be perceived by touch as well as by sight. What is meant by the indirect object of sense may be illustrated if we suppose that the white thing before you is Diares' son. You perceive Diares' son, but indirectly, for that which you perceive is accessory to the whiteness. Hence you are not affected by the indirect sensible as such. Of the two classes of sensibles directly perceived it is the objects special to the different senses which are properly perceptible: and it is to these that the essential character of each sense is naturally adapted.

The object, then, of sight is the visible: what is visible is colour and something besides which can be described, though it has no name. What we mean will best be made clear as we proceed. The visible, then, is colour. Now colour is that with which what is visible in itself is overlaid: and, when I say in itself, I do not mean what is visible by its essence or form, but what is visible because it contains within itself the cause of visibility, namely, colour. But colour is universally capable of exciting change in the actually transparent, that is, in light; this being, in fact, the true nature of colour. Hence colour is not visible without light, but the colour of each object is always seen in light. And so we shall have first to explain what light is.

There is, then, we assume, something transparent; and by this I mean that which, though visible, is not properly sneaking, visible in itself, but by reason of extrinsic colour. Air, water and many solid bodies answer to this description. For they are not transparent qua air or qua water,

but because there is a certain natural attribute present in both of them which is present also in the eternal body on high. Light is the actuality of this transparent. But where the transparent is only potentially present, there darkness is actually. Light is a sort of colour in the transparent when made transparent in actuality by the agency of fire or something resembling the celestial body: for this body also has an attribute which is one and the same with that of it. What the transparent is, and what light is, has now been stated; namely, that corporeal. + it is neither fire nor body generally nor an effluence from any body (for even then it would still be a sort of body), but the presence of fire or something fiery in the transparent. For it is impossible for two bodies to occupy the same space at the same time.

Light is held to be contrary to darkness. But darkness is absence from the transparent of the quality above described: so that plainly light is the presence of it. Thus Empedocles and others who propounded the same view are wrong when they represent light as moving in space and arriving at a given point of time between the earth and that which surrounds it without our perceiving its motion. For this contradicts not only the clear evidence of reason, but also the facts of observation: since, though a movement of light might elude observation within a short distance, that it should do so all the way from east to west is too much to assume.

It is that which is colourless which is receptive of colour, as it is that which is soundless which is receptive of sound. And the transparent is colourless, and so is the invisible or the dimly visible which is our idea of the dark. Such is the transparent medium, not indeed when it is in actuality, but when potentially transparent. For it is the same natural attribute which is at one time darkness and at another time light. It is not everything visible which is visible in light, but only the proper colour of each thing. Some things, indeed, are not seen in daylight, though they produce sensation in the dark: as, for example, the things of fiery and glittering appearance, for which there is no one distinguishing name, like fungus, horn,

the heads, scales and eyes of fishes. But in no one of these cases is the proper colour seen. Why these objects are seen must be discussed elsewhere. At present this much is clear, that the object seen in light is colour, and this is why it is not seen without light. For the very quiddity of colour is, as we saw, just this, that it is capable of exciting change in the operantly transparent medium: and the activity of the transparent is light. There is clear evidence of this. If you lay the coloured object upon your eye, you will not see it. On the contrary, what the colour excites is the transparent medium, say, the air, and by this, which is continuous, the sense-organ is stimulated. For it was a mistake in Democritus to suppose that if the intervening space became a void, even an ant would be distinctly seen, supposing there were one in the sky. That is impossible. For sight takes place through an affection of the sensitive faculty. Now it cannot be affected by that which is seen, the colour itself: therefore it can only be by the intervening medium: hence the existence of some medium is necessary. But, if the intermediate space became a void, so far from being seen distinctly, an object would not be visible at all.

We have explained the reason why colour must be seen in light. Fire is visible both in light and in darkness: and necessarily so, for it is owing to fire that the transparent becomes transparent. The same argument holds for sound and odour. For no sound or scent produces sensation by contact with the sense-organ: it is the intervening medium which is excited by sound and odour and the respective sense-organs by the medium. But, when the body which emits the sound or odour is placed on the sense-organ itself, it will not produce any sensation. The same holds of touch and taste, although it appears to be otherwise. The reason for this will be seen hereafter. The medium for sounds is air, that for odour has no name. For there is assuredly a common quality in air and water, and this quality, which is present in both, stands to the body which emits odour in the same relation as the transparent

to colour. For the animals that live in water also appear to have the sense of smell. But man and the other land-animals which breathe are unable to smell without inhaling breath. The reason for this, too, must be reserved for future explanation.

Let us now begin by determining the nature of sound and hearing. There are two sorts of sound, one a sound which is operant, the other potential sound. For some things we say have no sound, as sponge, wool; others, for example, bronze and all things solid and smooth, we say have sound, because they can emit sound, that is, they can produce actual sound between the sonorous body and the organ of hearing. When actual sound occurs it is always of something on something and in something, for it is a blow which produces it. Hence it is impossible that a sound should be produced by a single thing, for, as that which strikes is distinct from that which is struck, that which sounds sounds upon something. And a blow implies spatial motion. As we stated above, it is not concussion of any two things taken at random which constitutes sound. Wool, when struck, emits no sound at all, but bronze does, and so do all smooth and hollow things; bronze emits sound because it is smooth, while hollow things by reverberation produce a series of concussions after the first, that which is set in motion being unable to escape. Further, sound is heard in air and, though more faintly, in water. It is not the air or the water, however, which chiefly determine the production of sound: on the contrary, there must be solid bodies colliding with one another and with the air: and this happens when the air after being struck resists the impact and is not dispersed. Hence the air must be struck quickly and forcibly if it is to give forth sound; for the movement of the striker must be too rapid to allow the air time to disperse: just as would be necessary if one aimed a blow at a heap of sand or a sand-whirl, while it was in rapid motion onwards.

Echo is produced when the air is made to rebound backwards like a ball from some other air which has become a single mass owing to its being within a cavity which confines

it and prevents its dispersion. It seems likely that echo is always produced, but is not always distinctly audible: since surely the same thing happens with sound as with light. For light is always being reflected; else light would not be everywhere, but outside the spot where the sun's rays fall there would be darkness. But it is not always reflected in the same way as it is from water or bronze or any other smooth surface; I mean, it does not always produce the shadow, by which we define light.

Void is rightly stated to be the indispensable condition of hearing. For the air is commonly believed to be a void, and it is the air which causes hearing, when being one and continuous it is set in motion. But, owing to its tendency to disperse, it gives out no sound unless that which is struck is smooth. In that case the air when struck is simultaneously reunited because of the unity of the surface; for a smooth body presents a single surface.

That, then, is resonant which is capable of exciting motion in a mass of air continuously one as far as the ear. There is air naturally attached to the ear. And because the ear is in air, when the external air is set in motion, the air within the ear moves. Hence it is not at every point that the animal hears, nor that the air passes through: for it is not at every point that the part which is to set itself in motion and to be animate has a supply of air. Of itself, then, the air is a soundless thing because it is easily broken up. But, whenever it is prevented from breaking up, its movement is sound. But the air within the ears has been lodged fast within walls to make it immoveable, in order that it may perceive exactly all the varieties of auditory movement. This is why we hear in water also, because the water does not pass right up to the air attached to the ear, nor even into the ear at all, because of its convolutions. Should this happen, hearing is destroyed, as it is by an injury to the membrane of the tympanum, and as sight is by an injury to the cornea. Further, we have evidence whether we hear or not, according as there is or is not always a ringing sound in

the ears, as in a horn: for the air imprisoned there is always moving with a proper motion of its own. But sound is something of external origin and is not native to the ear. And this is why it is said that we hear by means of what is empty and resonant, because that by which we hear has air confined within it.

Does that which is struck emit the sound or that which strikes? Is it not rather both, but each in a different way? For sound is motion of that which is capable of being moved in the same Ianner as things rebound from smooth surfaces when struck sharply against them. Thus, as above remarked, it is not everything which, when struck or striking, emits sound: supposing, for instance, a pin were to strike against a pin, there would be no sound. The thing struck must be of even surface, so that the air may rebound and vibrate in one mass.

The varieties of resonant bodies are clearly distinguished by the sound they actually emit. For, as without light colours are not seen, so without sound we cannot distinguish high and low or acute and grave in pitch. These latter terms are used by analogy from tangible objects. For the acute, that is, the high, note moves the sense much in a little time, while the grave or low note moves it little in much time. Not that what is shrill is identically rapid, nor what is low is slow, but it is in the one case the rapidity, in the other the slowness, which makes the motion or sensation such as has been described. And it would seem that there is a certain analogy between the acute and grave to the ear and the acute and blunt to the touch. For that which is acute or pointed, as it were, stabs, while the blunt, as it were, thrusts, because the one excites motion in a short, the other in a long time, so that per accidens the one is quick, the other slow. Let this account of sound suffice.

Voice is a sound made by an animate being. No inanimate thing is vocal, though it may by analogy be said to be vocal, as in the case of the pipe, the lyre and all other inanimate things that have pitch and tune and articulation: for these qualities, it would seem, the voice also possesses. But many animals have no voice: that is to say, all bloodless animals and, among animals that have blood, fishes. And this is what we might expect, since sound is a movement of air. Those fishes which

are said to possess voice, such as those in the Achelous, merely make a noise with their gills or some other such part. Voice is sound made by an animal, and not by any part of its body indifferently. But, as in every case of sound there is something that strikes, something struck and a medium, which is air, it is reasonable that only creatures which inhale air should have voice. For here nature uses the air that is inhaled for two purposes, just as it uses the tongue for tasting and for speech, the former use, for tasting, being indispensable and therefore more widely found, while expression of thought is a means to well-being. Similarly nature uses the breath first as a necessary means to the maintenance of internal warmth (the reason for which shall be explained elsewhere) and, further, as a means of producing voice and so promoting well-being. The organ of respiration is the larynx, and the part to which this part is subservient is the lung: for it is this organ, namely, the lung, which enables land animals to maintain a higher temperature than others. Respiration is also needed primarily for the region about the heart. Hence, as we draw breath, the air enters: and so the impact upon the windpipe, as it is called, of the air breathed is voice, the cause of the impact being the soul which animates the vocal organs. For, as we said before, it is not every sound made by an animal that is voice. Noise can be produced even with the tongue or as in coughing: but it is necessary for voice that the part which strikes should be animate and that some mental image should be present. For voice is certainly a sound which has significance and is not like a cough, the noise of air respired: rather with this air the animal makes the air in the windpipe strike against the windpipe. A proof of this is the fact that we cannot speak while inhaling or exhaling breath, but only while we hold it in: for anyone who holds his breath uses the breath so held to cause motion. And it is evident why fishes are voiceless. It is because they have no larynx. And they are without this part because they do not take in the air nor breathe. Why this is so does not concern us here.

Of smell and the object of smell it is less easy to speak definitely than of the senses above-mentioned: for the nature of odour is by no means so clear as is the nature of sound or of colour. The reason is that this sense in us is not exact, but inferior to that of many animals. In fact, man has a poor olfactory sense and perceives none of the objects of smell unless they be painful or pleasant, which implies that the organ is wanting in accuracy. It is reasonable to suppose that animals with hard eyes perceive colour in the same vague way and do not distinguish the varieties of colour except in so far as they do, or do not, inspire fear. And this is the way in which mankind perceive odours. For it would seem that, while there is an analogy to taste and the varieties of flavour answer to the varieties of smell, our sense of taste is more exact because it is a modification of touch and the sense of touch is the most exact of man's senses. In the other senses man is inferior to many of the animals, but in delicacy of touch he is far superior to the rest. And to this he owes his superior intelligence. This may be seen from the fact that it is this organ of sense and nothing else which makes all the difference in the human race between the natural endowments of man and man. For hard-skinned men are dull of intellect, while those who are soft-skinned are gifted.

As with flavours, so with odours: some are sweet, some bitter. (But in some objects smell and flavour correspond; for example, they have sweet odour and sweet flavour: in other of odour ~~ things the opposite is the case.) Similarly, too, an odour may be pungent, irritant, acid or oily. But because, as we said above, odours are not as clearly defined as the corresponding flavours, it is from these latter that the odours have taken their names, in virtue of the resemblance in the things. Thus the odour of saffron and honey is sweet, while the odour of thyme and the like is pungent; and so in all the other cases. Again, smell corresponds to hearing and to each of the other senses in that, as hearing is of the audible and inaudible, and

sight of the visible and invisible, so smell is of the odorous and inodorous. By inodorous may be meant either that which is wholly incapable of having odour or that which has a slight or faint odour. The term tasteless involves a similar ambiguity.

Further, smell also operates through a medium, namely, air or water. For water animals, too, whether they are, or are not, possessed of blood, seem to perceive odour as much as the creatures in the air: since some of them also come from a great distance to seek their food, guided by the scent.

Hence there is an obvious difficulty, if the process of smell is the same everywhere, and yet man smells when inhaling but does not smell when instead of inhaling he is exhaling or holding his breath, no matter whether the object be distant or near, or even if it be placed on the inside of the nostril. The inability to perceive what is placed immediately on the sense-organ man shares with all animals: what is peculiar to him is that he cannot smell without inhaling. This is made plain by experiment. Consequently bloodless animals, since they do not breathe, might be thought to have a distinct sense other than those commonly recognised. But, we reply, that is impossible, since it is odour which they perceive. For perception of odour, be it fragrant or noisome, constitutes smelling. Moreover, it is found that these bloodless animals are destroyed by the same powerful odours as man, such as asphalt, brimstone and the like. It follows then that they do smell, but not by inhaling breath.

It would seem, again, that in man the organ of this sense differs from that of the other animals, as his eyes differ from those of hard-eyed animals. Man's eyes have, in the eyelids, a sort of screen or sheath and without moving or opening them he cannot see: while the hard-eyed animals have nothing of the kind, but at once see whatever is taking place in the transparent medium. So, too, it seems, the organ of smell in some animals is unenclosed, just as is the eye, but in those which take in the air it has a curtain, which is removed in the process of inhaling, by dilatation of the veins and passages. And this is the

reason why animals which breathe cannot smell in the water. For it is necessary for them to take in breath before smelling and this they cannot do in the water. Odour is included under that which is dry, as flavour under that which is moist, and the organ of smell is potentially dry also.

The object of taste is a species of tangible. And this is the reason why it is not perceived through a foreign body as medium: for touch employs no such medium either. The body, too, in which the flavour resides, the proper object of taste, has the moist, which is something tangible, for its external matter or vehicle. Hence, even if we lived in water, we should still perceive anything sweet thrown into the water, but our perception would not have come through the medium, but by the admixture of sweetness with the fluid, as is the case with what we drink. But it is not in this way, namely, by admixture, that colour is perceived, nor yet by emanations. Nothing, then, corresponds to the medium; but to colour, which is the object of sight, corresponds the flavour, which is the object of taste. But nothing produces perception of flavour in the absence of moisture, but either actually or potentially the producing cause must have liquid in it: salt, for instance, for that is easily dissolved and acts as a dissolvent upon the tongue.

Again, sight is of the invisible as well as the visible (for darkness is invisible and this, too, sight discerns as well as light) and, further, of that which is exceedingly bright, which is likewise invisible, though in a different way from darkness. Similarly hearing has to do with noise and silence, the former being audible, the latter inaudible, and, further, with loud noise, to which it is related as vision is to brightness, a loud and a violent sound being in a manner just as inaudible as a faint sound. The term invisible, be it noted, is applied not only to that which it is wholly impossible to see, which corresponds to other cases of the impossible, but also when a thing has imperfectly or not at all its natural properties, answering to the footless and the kernel-less. So, too, taste has for object The object mot only that which can be tasted, but also the tasteless, of taste. = by which we mean that which has little flavour or hardly any at all, or a flavour destructive of the taste. Now in flavour this distinction is supposed to start with the drinkable and the

undrinkable. Both are tastes of a sort, but the latter is poor or destructive of the faculty of taste, while the former is naturally adapted to it. The drinkable is the common object of touch and of taste. But, since the object of taste is moist, the sense-organ which perceives it must be neither actually moist nor yet incapable of becoming moist. For taste is acted upon by the object of taste as such. The organ of taste, then, which needs to be moistened, must have the capacity of absorbing moisture without being dissolved, while at the same time it must not be actually moist. A proof of this is the fact that the tongue has no perception either when very dry or very moist. In the latter case the contact is with the moisture originally in the tongue, just as when a man first makes trial of a strong flavour and then tastes some other flavour; or as with the sick, to whom all things appear bitter because they perceive them with their tongue full of bitter moisture.

As with the colours, so with the species of flavour, there are, Species of firstly, simple flavours, which are opposites, the sweet and the bitter; next to these on one side the succulent, on the other the salt; and, thirdly, intermediate between these, the pungent, the rough, the astringent and the acid.'These seem to be practically all the varieties of flavour. Consequently, while the faculty of taste has potentially the qualities just described, the object of taste converts the potentiality into actuality.

The same account is to be given of touch and the tangible. If touch is not a single sense but includes more senses than one, there must be a plurality of tangible objects also. It is a question whether touch is several senses or only one. What, moreover, is the sense-organ for the faculty of touch? Is it the flesh or what is analogous to this in creatures that have not flesh? Or is flesh, on the contrary, the medium, while the primary sense-organ is something different, something internal? We may argue thus: every sense seems to deal with a single pair of opposites, sight with white and black, hearing with high and low pitch, taste with bitter and sweet; but under the tangible are included several pairs of opposites, hot and cold, dry and moist, hard and soft and the like. A partial solution of this difficulty lies in the consideration that the other senses also apprehend more than one pair of opposites. Thus in vocal sound there is not only high and low pitch, but also loudness and faintness, smoothness and roughness, and soon. In regard to colour also there are other similar varieties. But what the one thing is which is subordinated to touch as sound is to hearing is not clear.

But is the organ of sense internal or is the flesh the immediate organ? No inference can be drawn, seemingly, from the fact that the sensation occurs simultaneously with contact. For even under present conditions, if a sort of membrane were constructed and stretched over the flesh, this would immediately on contact transmit the sensation as before. And yet it is clear that the organ of sense is not in this membrane; although, if by growth it became united to the flesh, the sensation would be transmitted even more quickly. Hence it appears that the part of the body in question, that is, the flesh, is related to us as the air would be if it were united to us all round by natural growth. We should then have thought we were perceiving sound, colour and smell by one and the same instrument: in fact, sight, hearing and smell would have seemed to us in a manner to constitute a single sense. But as it is, owing to the media, by which the various motions are transmitted, being separated from us, the difference of the organs of these three senses is manifest. But in regard to touch this point is at present obscure.

In fact, the animate body cannot consist of air or water singly, it must be something solid. The only alternative is that it should be a compound of earth and of these elements, as flesh and what is analogous to flesh profess to be. Consequently the body must be the naturally cohering medium for the faculty of touch, through which the plurality of sensations is communicated. That they are a plurality is made clear by touch in the case of the tongue, for the tongue perceives all tangible objects, and that at the same part at which it perceives flavour. Now, if the rest of the flesh also had perception of flavour, taste and touch would have seemed to be one and the same sense: whereas they are really two, because their organs are not interchangeable.

Here a question arises. All body has depth, this being the third dimension, and, if between two bodies a third body is interposed, the two cannot touch one another. Now that which is fluid is not independent of body, nor is that which is wet: if it is not itself water, it must contain water. But when bodies touch one another in the water, since their exterior surfaces are not dry, there must be water between them, the water with which their extremities are flooded. If, then, all this be true, no one thing can possibly touch another in the water, nor yet in the air: for the air stands to the objects in the air as water to the things in water, but this fact we are more apt to overlook, just as aquatic animals fail to notice that the things which touch one another in the water have wet surfaces. The question then arises: is the mode of perception uniform for all objects or does it differ for different objects? According to the prevalent view, taste and touch operate by direct contact, while the other senses operate at a distance. But this view ts incorrect. On the contrary, we perceive the hard and the soft also mediately, just as much as we do the resonant, the visible, the odorous. But the latter are perceived at a distance, the former close at hand: and this is why the fact escapes us, since we really perceive all objects through a medium, though in touch and taste we fail to notice this. And yet, as we mentioned above, even if we perceived all objects of touch through a membrane without being aware of its interference, we should be just in the same position as we are now with regard to objects in the water or in the air: for, as it is, we suppose that we are touching the objects themselves and that there is no intervening medium. But there is this difference between the tangible on the one hand and visible and resonant things on the other: the latter we perceive because the medium acts in a certain way upon us, while tangible objects we perceive not by any action upon us of the medium, but concurrently with it, like the man who is struck through his shield. It is not that the shield was first struck and then passed on the blow, but, as it happened, both were struck simultaneously. And, generally, it would seem that the flesh and the tongue are related

to the true sense-organ as are air and water to the organs of sight, hearing and smell respectively. But neither in the one case nor in the other would sensation follow on contact with the sense-organ; for instance, if a body that is white were placed on the outer surface of the eye: which shows that the instrument that apprehends the tangible is within. We should then get the same result as in the case of the other senses. What is placed on the sense-organ we do not perceive: what is placed on the flesh we do perceive: therefore flesh is the medium for the faculty of touch.

It is, then, the distinctive qualities of body as body which are the objects of touch: I mean those qualities which determine the Clements, hot or cold, dry or moist, of which we have previously given an account in our discussion of the elements. And their sense-organ, the tactile organ, that is, in which the sense called touch primarily resides, is the part which has potentially the qualities of the tangible object. For perceiving is a sort of suffering or being acted upon: so that when the object makes the organ in actuality like itself it does so because that organ is potentially like it. Hence it is that we do not perceive what is just as hot or cold, hard or soft, as we are, but only the excesses of these qualities: which implies that the sense is a kind of mean between the opposite extremes in the sensibles. This is why it passes judgment on the things of sense. For the mean is capable of judging, becoming to each extreme in turn its opposite. And, as that which is to perceive white and black must not be actually either, though potentially both, and similarly for the other senses also, so in the case of touch the organ must be neither hot nor cold. Further, sight is in a manner, as we saw, of the invisible as well as the visible, and in the same way the remaining senses deal with opposites. So, too, touch is of the tangible and the intangible: where by intangible is meant, first, that which has the distinguishing quality of things tangible in quite a faint degree, as is the case with the air; and, secondly, tangibles which are in excess, such as those which are positively destructive. Each of the senses, then, has now been described in outline.