Book II, Chapter 9

Smell and the object of smell are less easy to determine than the matters we have discussed, for it is not clear what sort of thing smell is, in the way that it is clear what sound or colour is. The reason is that we do not possess this sense in an accurate form, but a worse one than many animals have; for man smells poorly, and perceives none of the objects of smell apart from the painful or the pleasant, since the sense-organ is not accurate. And it is reasonable to suppose that the hard-eyed animals perceive colours in this same way, and that the differences of colours are not distinct to them, save in respect of the frightening and the unfrightening. So it is with the human race in the case of smells.

For smell seems to be analogous to taste, and the kinds of flavours to correspond in like manner to those of smell; but we possess the sense of taste in a more accurate form, because it is a kind of touch, and man has this sense in the most accurate form of all. For in the other senses he falls far short of the animals, but in respect of touch he discriminates far more accurately than the rest. And this is why he is the most intelligent of animals. A sign of it is that within the human race it is in virtue of this sense-organ, and of no other, that men are well or ill endowed by nature; for those with hard flesh are ill endowed in mind, while those with soft flesh are well endowed.

As one flavour is sweet and another bitter, so it is also with smells. But some things have a smell and a flavour that correspond — I mean, for instance, a sweet smell and a sweet flavour — while with others it is the reverse. In like manner a smell may be pungent, harsh, sharp, or oily. But, as we said, because smells are not as clearly distinguished as flavours are, they have taken their names from the latter in virtue of a resemblance in the things themselves; for the sweet smell is so called from saffron and honey, the pungent from thyme and the like, and in the same way with the rest.

And as hearing is of the audible and the inaudible, and each of the other senses likewise — sight of the visible and the invisible — so smell is of the smellable and the unsmellable. A thing is unsmellable either because it is wholly incapable of having a smell, or because it has a slight and poor one. And "tasteless" is used in the same way.

Smelling too takes place through a medium, such as air or water; for water animals also seem to perceive smell, and this alike in the blooded and the bloodless, just as much as those that live in air. For some of these last come from a long way off to their food, having caught the scent of it.

Hence there appears to be a difficulty, if all animals smell alike, and yet man smells when he breathes in, but when he is not breathing in — whether he is breathing out or holding his breath — does not smell, neither from far off nor from close at hand, not even if the object be placed inside the nostril. That what is placed upon the sense-organ itself should be imperceptible is common to all the senses; but to perceive nothing without breathing is peculiar to men, as is clear to those who make the trial. So that the bloodless animals, since they do not breathe, would have to possess some further sense besides those we have named. But this is impossible, if it is smell that they perceive; for the perception of what is odorous, whether ill-smelling or fragrant, just is smelling. Again, they are evidently destroyed by the same strong smells that destroy man, such as bitumen and sulphur and the like. They must therefore smell, and yet without breathing.

It seems that in men this sense-organ differs from that of the other animals in the way that men's eyes differ from those of the hard-eyed animals. For men's eyes have in the eyelids a screen and, as it were, a sheath, and unless a man moves these and draws them back he does not see; whereas the hard-eyed animals have nothing of the sort, but see at once whatever comes to be in the transparent. So too, then, the organ of smell is in some animals uncovered, like the eye, while in those that take in air it has a covering, which is drawn back when they breathe in, as the small vessels and the passages are dilated. And this is why animals that breathe do not smell in water; for they must breathe in order to smell, and to do this in water is impossible.

Smell belongs to what is dry, as flavour belongs to what is moist; and the organ of smell is potentially such.

Book II, Chapter 10

The object of taste is a kind of tangible object; and this is the reason why it is not perceptible through a medium consisting of a foreign body, for neither is the object of touch. And the body in which the flavour resides, that is, the object of taste, is in what is moist as in its matter; and this is something tangible. Hence, even if we lived in water, we should perceive a sweet thing that was thrown into it; but our perception would not have come to us through the medium, but by the sweet thing's being mixed with the liquid, just as in the case of a drink. Colour, on the other hand, is not seen in this way, by being mixed, nor yet by effluences. In the case of taste, then, there is nothing that corresponds to the medium; but as colour is the visible object, so flavour is the object of taste.

But nothing produces a perception of flavour without moisture; what produces it must have moisture either actually or potentially, as the salty does: for salt is itself easily dissolved, and it is a solvent of the tongue.

And just as sight is of both the visible and the invisible (for darkness is invisible, and yet sight discriminates this too), and further of what is exceedingly bright (for this also is invisible, though in a different way from darkness), so likewise hearing is of sound and of silence, of which the one is audible and the other not audible, and also of a very loud sound, as sight is of the exceedingly bright. For as a faint sound is in a way inaudible, so too is a loud and violent one. Now "invisible" is said in one sense of what is so absolutely, as in other cases we speak of the impossible, and in another sense of that which, though naturally fitted to have the quality, has it not at all or has it poorly, as we call a thing "footless" or "stoneless." So too taste is of the tasteable and of the tasteless; and the tasteless is that which has a slight or a poor flavour, or which is destructive of taste.

The starting-point here seems to be the drinkable and the undrinkable; for both are in a way objects of taste, but the one is a poor object and destructive of taste, while the other is according to nature. And the drinkable is common to touch and to taste.

And since the object of taste is moist, its sense-organ too must be neither moist in actuality nor incapable of being moistened; for taste is affected in some way by the object of taste, qua object of taste. The organ of taste, then, must be moistened — being such as can be moistened while remaining unimpaired, and yet not being itself moist. A sign of this is that the tongue perceives neither when it is quite dry nor when it is too moist; for in the latter case the contact is with the moisture already present in it, as happens when a man who has first tasted a strong flavour then tastes another; and it is in this way that to the sick everything appears bitter, because they perceive with a tongue that is full of such moisture.

The kinds of flavour, as also in the case of colours, are these: the simple ones are the contraries, the sweet and the bitter; next to the one comes the oily and next to the other the salty; and between these lie the pungent, the harsh, the astringent and the acid. For these are pretty well all the varieties of flavour that are thought to exist. So that the faculty of taste is what is potentially such, while the object of taste is what makes it so in actuality.

Book II, Chapter 11

Concerning the tangible and touch the same account holds. For if touch is not one sense but several, then the tangible objects of perception must also be several. But there is a difficulty whether they are several or one, and also what the sense-organ of the tangible is, the organ of touch: whether it is the flesh, and in the other animals what is analogous to flesh, or not, but this is rather the medium, while the primary sense-organ is something else within.

For every sense seems to be concerned with a single pair of contraries, as sight with white and black, hearing with high and low pitch, and taste with bitter and sweet; but in the tangible there are many pairs of contraries — hot and cold, dry and moist, hard and soft, and all the others of this kind. There is, however, some solution to this difficulty at least, namely that in the other senses too there are several pairs of contraries: for instance in the voice there is not only highness and lowness of pitch, but also loudness and faintness, and smoothness and roughness of voice, and other such differences. And there are other such differences in the case of colour as well. But what the one underlying subject is for touch, corresponding to sound for hearing, is not clear.

Is the sense-organ, then, within, or is it not, but the flesh directly? It seems to be no proof that the perception arises at the very moment when the objects are touched. For even as things are, if one were to stretch round the flesh a sort of membrane made for the purpose, it would report the sensation in just the same way as soon as it was touched; and yet it is clear that the sense-organ is not in this membrane. And if the membrane were actually grown on to the flesh, the sensation would penetrate more quickly still. Hence this part of the body seems to stand to us as the air would stand if it had grown naturally round about us in a ring; for then we should have supposed that we perceive sound and colour and smell by one and the same thing, and that sight, hearing and smell are a single sense. But as it is, because that through which the movements take place is marked off separately, the sense-organs mentioned are evidently different from one another.

In the case of touch, however, this is at present obscure. For the ensouled body cannot be composed of air or of water, since it must be something solid. It remains, then, that it is a mixture of earth and of these, such as flesh and its analogue tend to be; so that the body too must be the medium of the faculty of touch, naturally attached to it, through which the perceptions, being several, come about. That they are several is shown by touch in the tongue; for it perceives all tangible objects, and flavour as well, with the same part. If, then, the rest of the flesh also perceived flavour, taste and touch would seem to be one and the same sense; but as it is they are two, because the relation is not convertible.

One might raise this difficulty. If every body has depth, this being the third dimension, and if two bodies have some body between them, then these cannot touch one another. But the moist does not exist without body, nor does the wet, but it must either be water or contain water. And things that touch one another in water, since their surfaces are not dry, must have water between them, with which their extremities are filled. But if this is true, it is impossible for one thing to touch another in water. And it is the same way in air too; for air stands to the things in it as water does to the things in water. But it escapes our notice more, just as it escapes the notice of animals living in water whether one wet thing touches another wet thing.

Is perception, then, alike in the case of all objects, or does it come about differently for different ones, as it now seems that taste and touch operate by contact, while the rest operate at a distance? But this is not so. On the contrary, we perceive the hard and the soft as well through other things, just as we perceive that which sounds and that which is visible and that which has an odour; only the latter are perceived from far off, the former from close at hand. And that is why the fact escapes our notice; since we do in truth perceive all objects through the medium, but in these cases the medium passes unnoticed.

And yet, as we said before as well, even if we were to perceive all tangible objects through a membrane, without noticing that it kept us apart from them, we should be in just the same case as we now are in water and in air; for as things are we suppose that we touch the objects themselves and that there is nothing between. But the tangible differs from the visible and from that which sounds in this respect: of those we have perception because the medium acts in some way upon us, whereas of tangible objects we have perception not by the agency of the medium but at the same time as the medium, like the man who is struck through his shield; for it was not that the shield, having been struck, then struck him, but it happened that both were struck at once.

In general, the flesh and the tongue seem to stand to the sense-organ as air and water stand to sight and hearing and smell, each of those media standing in the same way to its own organ. But if the sense-organ itself were touched, no perception would arise either in that case or in this, as if a man were to lay a white body upon the outermost surface of the eye. From which it is also plain that what perceives the tangible is within. For only so would there come about what comes about in the other cases as well: when objects are laid upon the sense-organ there is no perception, but when they are laid upon the flesh there is. Hence the flesh is the medium of the faculty of touch.

Tangible, then, are the distinguishing qualities of body qua body; and by distinguishing qualities I mean those which mark off the elements — hot and cold, dry and moist — concerning which we have spoken earlier in our discussion of the elements. And the sense-organ of these, the organ of touch, that in which primarily the sense called touch resides, is the part which is potentially such as they are; for to perceive is to be affected in some way. So that what acts makes the other, which is potentially such, become such as the agent itself is in actuality.

This is why we do not perceive what is equally hot and cold with ourselves, or equally hard and soft, but only the excesses of these, the sense being, as it were, a kind of mean between the contrariety that resides in perceptible objects. And it is for this reason that it discriminates perceptible objects; for the mean is what discriminates, since in relation to each of the extremes it becomes the other of them. And just as that which is to perceive white and black must be neither of them in actuality, but both potentially, so it is in the other cases too, and in the case of touch the organ must be neither hot nor cold.

Further, just as sight was in a way of the visible and of the invisible, and likewise the remaining senses of their respective opposites, so touch too is of the tangible and of the intangible. And the intangible is both that which has an altogether slight degree of the distinguishing quality of tangible things, as is the case with air, and also the excesses among tangible objects, such as those that are destructive.

Concerning each of the senses, then, an account has now been given in outline.