by Aristotle
We have now explained what the transparent is and what light is; light is [15] neither fire nor any kind whatsoever of body nor an efflux from any kind of body (if it were, it would again itself be a kind of body)—it is the presence of fire or something resembling fire in what is transparent. It is certainly not a body, for two bodies cannot be present in the same place. The opposite of light is darkness; darkness is the absence from what is transparent of the corresponding positive state [20] above characterized; clearly therefore, light is just the presence of that.
Empedocles (and with him all others who used the same forms of expression) was wrong in speaking of light as ‘travelling’ or being at a given moment between the earth and its envelope, its movement being unobservable by us; that view is contrary both to the clear evidence of argument and to the observed facts; if the [25] distance traversed were short, the movement might have been unobservable, but where the distance is from extreme East to extreme West, the strain upon our powers of belief is too great.
What is capable of taking on colour is what in itself is colourless, as what can take on sound is what is soundless; what is colourless includes what is transparent and what is invisible or scarcely visible, i.e. what is dark. The latter is the same as [30] what is transparent, when it is potentially, not of course when it is actually transparent; it is the same substance which is now darkness, now light.
[419a1] Not everything that is visible depends upon light for its visibility. This is only true of the ‘proper’ colour of things. Some objects of sight which in light are invisible, in darkness stimulate the sense; that is, things that appear fiery or shining. This class of objects has no simple common name, but instances of it are fungi, [5] horns, heads, scales, and eyes of fish. In none of these is what is seen their own proper colour. Why we see these at all is another question. At present what is obvious is that what is seen in light is always colour. That is why without the help of light colour remains invisible. Its being colour at all means precisely its having in it the power to set in movement what is actually transparent, and the actuality of what [10] is transparent is just light.
The following makes the necessity of a medium clear. If what has colour is placed in immediate contact with the eye, it cannot be seen. Colour sets in movement what is transparent, e.g. the air, and that, extending continuously from the object of the organ, sets the latter in movement. Democritus misrepresents the [15] facts when he expresses the opinion that if the interspace were empty one could distinctly see an ant on the vault of the sky; that is an impossibility. Seeing is due to an affection or change of what has the perceptive faculty, and it cannot be affected by the seen colour itself; it remains that it must be affected by what comes between. Hence it is indispensable that there be something in between—if there were [20] nothing, so far from seeing with greater distinctness, we should see nothing at all.
We have now explained the cause why colour cannot be seen otherwise than in light. Fire on the other hand is seen both in darkness and in light; this double possibility follows necessarily from our theory, for it is just fire that makes what is potentially transparent actually transparent.
The same account holds also of sound and smell; if the object of either of these [25] senses is in immediate contact with the organ no sensation is produced. In both cases the object sets in movement only what lies between, and this in turn sets the organ in movement: if what sounds or smells is brought into immediate contact with the organ, no sensation will be produced. The same, in spite of all appearances, applies also to touch and taste; why there is this apparent difference will be clear [30] later. What comes between in the case of sounds is air; the corresponding medium in the case of smell has no name. But, corresponding to what is transparent in the case of colour, there is a quality found both in air and water, which serves as a medium for what has smell; for animals that live in water seem to possess the sense of smell. Men and all other land animals that breathe, perceive smells only when they [419b1] breathe air in. The explanation of this too will be given later.
8 · Now let us, to begin with, make certain distinctions about sound and hearing.
Sound may mean either of two things—actual and potential sound. There are [5] certain things which, as we say, have no sound, e.g. sponges or wool, others which have, e.g. bronze and in general all things which are smooth and solid—the latter are said to have a sound because they can make a sound, i.e. can generate actual sound between themselves and the organ of hearing.
Actual sound is always of something in relation to something and in something; for it is generated by an impact. Hence it is impossible for one body only [10] to generate a sound—there must be a body impinging and a body impinged upon; what sounds does so by striking against something else, and this is impossible without a movement from place to place.
As we have said, not all bodies can by impact on one another produce sound; impact on wool makes no sound, while the impact on bronze or any body which is smooth and hollow does. Bronze gives out a sound when struck because it is smooth; [15] bodies which are hollow owing to reflection repeat the original impact over and over again, the body originally set in movement being unable to escape from the concavity.
Further, sound is heard both in air and in water, though less distinctly in the latter. Yet neither air nor water is the principal cause of sound. What is required for [20] the production of sound is an impact of two solids against one another and against the air. The latter condition is satisfied when the air impinged upon does not retreat before the blow, i.e. is not dissipated by it.
That is why it must be struck with a sudden sharp blow, if it is to sound—the movement of the whip must outrun the dispersion of the air, just as one16 might get in a stroke at a heap or whirl of sand as it was travelling rapidly past.
[25] An echo occurs, when, a mass of air having been unified, bounded, and prevented from dissipation by the containing walls of a vessel, the air rebounds from this mass of air like a ball from a wall. It is probable that in all generation of sound echo takes place, though it is frequently only indistinctly heard. What happens here must be analogous to what happens in the case of light; light is always reflected—[30] otherwise it would not be diffused and outside what was directly illuminated by the sun there would be blank darkness; but this reflected light is not always strong enough, as it is when it is reflected from water, bronze, and other smooth bodies, to cast a shadow, which is the distinguishing mark by which we recognize light.
It is rightly said that an empty space plays the chief part in the production of hearing, for people think that the air is empty, and the air is what causes hearing, [420a1] when it is set in movement as one continuous mass; but owing to its friability it emits no sound, unless what is impinged upon is smooth. But then it becomes a single mass at the same time because of the surface; for the surface of the smooth object is single.
What has the power of producing sound is what has the power of setting in movement a single mass of air which is continuous up to the organ of hearing. The organ of hearing is physically united with air, and because it is in air, the air inside [5] is moved concurrently with the air outside. Hence animals do not hear with all parts of their bodies, nor do all parts admit of the entrance of air; for even the part which can be moved and can sound has not air everywhere in it. Air in itself is, owing to its friability, quite soundless; only when its dissipation is prevented is its movement sound. The air in the ear is built into a chamber just to prevent this dissipating [10] movement, in order that the animal may accurately apprehend all varieties of the movements of the air outside. That is why we hear also in water, viz. because the water cannot get into the air chamber or even, owing to the spirals, into the outer ear. If this does happen, hearing ceases, as it also does if the tympanic membrane is damaged, just as sight ceases if the membrane covering the pupil is damaged. It is [15] also a sign of whether we hear or not that the ear does or does not reverberate like a horn; the air inside the ear has alw
ays a movement of its own, but the sound we hear is always the sounding of something else, not of the organ itself. That is why we say that we hear with what is empty and echoes, viz. because what we hear with is a chamber which contains a bounded mass of air.
Which is it that sounds, the striking body or the struck? Is not the answer that [20] it is both, but each in a different way? Sound is a movement of what can rebound from a smooth surface when struck against it. As we have explained not everything sounds when it strikes or is struck, e.g. if one needle is struck against another, neither emits any sound. In order, therefore, that sound may be generated, what is struck must be smooth, to enable the air to rebound and be shaken off from it in one [25] piece.
The distinctions between different sounding bodies show themselves only in actual sound; as without the help of light colours remain invisible, so without the help of actual sound the distinctions between sharp and flat sounds remain inaudible. Sharp and flat are here metaphors, transferred from their proper sphere, viz. that of touch, where they mean respectively what moves the sense much in a [30] short time, and what moves the sense little in a long time. Not that what is sharp really moves fast, and what is flat, slowly, but that the difference in the qualities of the one and the other movement is due to their respective speeds. There seems to be a sort of parallelism between what is sharp or flat to hearing and what is sharp or [420b1] blunt to touch; what is sharp as it were stabs, while what is blunt pushes, the one producing its effect in a short, the other in a long time, so that the one is quick, the other slow.
Let the foregoing suffice as an analysis of sound. Voice is a kind of sound [5] characteristic of what has soul in it; nothing that is without soul utters voice, it being only by a metaphor that we speak of the voice of the flute or the lyre or generally of what (being without soul) possesses the power of producing a succession of notes which differ in length and pitch and timbre. The metaphor is based on the fact that all these differences are found also in voice. Many animals are voiceless, e.g. all non-sanguineous animals and among sanguineous animals fish. [10] This is just what we should expect, since voice is a certain movement of air. The fish, like those in the Achelous, which are said to have voice, really make the sounds with their gills or some similar organ. Voice is the sound made by an animal, and that with a special organ. As we saw, everything that makes a sound does so by the impact of something against something else, across a space filled with air; hence it is [15] only to be expected that no animals utter voice except those which take in air. Once air is inbreathed, Nature uses it for two different purposes, as the tongue is used both for tasting and for articulating; in that case of the two functions tasting is necessary for the animal’s existence (hence it is found more widely distributed), while articulate speech serves its possessor’s well-being; similarly in the former case Nature employs the breath both as an indispensable means to the regulation of the [20] inner temperature of the living body and also as the matter of articulate voice, in the interests of its possessor’s well-being. Why its former use is indispensable must be discussed elsewhere.
The organ of respiration is the windpipe, and the organ to which this is related as means to end is the lungs. The latter is the part of the body by which the [25] temperature of land animals is raised above that of all others. But what primarily requires the air drawn in by respiration is not only this but the region surrounding the heart. That is why when animals breathe the air must penetrate inwards.
Voice then is the impact of the inbreathed air against the windpipe, and the agent that produces the impact is the soul resident in these parts of the body. Not [30] every sound, as we said, made by an animal is voice (even with the tongue we may merely make a sound which is not voice, or without the tongue as in coughing); what produces the impact must have soul in it17 and must be accompanied by an act of imagination, for voice is a sound with a meaning, and is not the result of any impact [421a1] of the breath as in coughing; in voice the breath in the windpipe is used as an instrument to knock with against the walls of the windpipe. This is confirmed by our inability to speak when we are breathing either out or in—we can only do so by holding our breath; we make the movements with the breath so checked. It is clear [5] also why fish are voiceless; they have no windpipe. And they have no windpipe because they do not breathe or take in air. Why they do not is a question belonging to another inquiry.
9 · Smell and its object are much less easy to determine than what we have hitherto discussed; the distinguishing characteristic of smell is less obvious than those of sound or colour. The ground of this is that our power of smell is less [10] discriminating and in general inferior to that of many species of animals; men have a poor sense of smell and our apprehension of its objects is bound up with pleasure and pain, which shows that in us the organ is inaccurate. It is probable that there is a parallel failure in the perception of colour by animals that have hard eyes: [15] probably they discriminate differences of colour only by the presence or absence of what excites fear, and that it is thus that human beings distinguish smells. It seems that there is an analogy between smell and taste, and that the species of tastes run parallel to those of smells—the only difference being that our sense of taste is more discriminating because it is a sort of touch, which reaches in man the maximum of [20] discriminative accuracy. While in respect of all the other senses we fall below many species of animals, in respect of touch we far excel all other species in exactness of discrimination. That is why man is the most intelligent of all animals. This is confirmed by the fact that it is to differences in the organ of touch and to nothing else that the differences between man and man in respect of natural endowment are [25] due; men whose flesh is hard are ill-endowed with intellect, men whose flesh is soft, well-endowed.
As flavours may be divided into sweet and bitter, so with smells. In some things the flavour and the smell have the same quality, e.g. both are sweet, in others they [30] diverge. Similarly a smell may be pungent, astringent, acid, or succulent. But, as we said, because smells are much less easy to discriminate than flavours, the names of [421b1] these varieties are applied to smells in virtue of similarity; for example sweet belongs to saffron or honey, pungent to thyme, and so on.
In the same sense in which hearing has for its object both the audible and the inaudible, sight both the visible and the invisible, smell has for its object both the [5] odorous and the inodorous. Inodorous may be either what has no smell at all, or what has a small or feeble smell. The same holds of the tasteless.
Smelling too takes place through a medium, i.e. through air or water—for water-animals too (both sanguineous and non-sanguineous) seem to smell just as [10] much as land-animals; at any rate some of them make directly for their food from a distance if it has any scent. That is why the following facts constitute a problem for us. All animals smell in the same way, but man smells only when he inhales; if he exhales or holds his breath, he ceases to smell, no difference being made whether the [15] odorous object is distant or near, or even placed inside the nostril; it is common to all not to perceive what is in immediate contact with the organ of sense, but our failure to apprehend what is odorous without the help of inhalation is peculiar to man (the fact is obvious on making the experiment). Now since bloodless animals do not breathe, they should have some other sense apart from those mentioned. But this is [20] impossible, since it is scent that is perceived; a sense that apprehends what is odorous and what has a good or bad odour cannot be anything but smell. Further, they are observed to be deleteriously effected by the same strong odours as man is, e.g. bitumen, sulphur, and the like. These animals must be able to smell without [25] breathing. The probable explanation is that in man the organ of smell has a certain superiority over that in all other animals just as his eyes have over those of hard-eyed animals. Man’s eyes have in the eyelids a kind of shelter or envelope, which must be shifted or drawn back in order that we may see, while hard-eyed [30] animals have nothing of the kind, but at once see wha
tever presents itself in the transparent medium. Similarly in certain species of animals the organ of smell is like the eye of hard-eyed animals, uncurtained, while in others which take in air it [422a1] probably has a curtain over it, which is drawn back in inhalation, owing to the dilating of the veins or pores. That explains also why animals that breathe cannot smell under water; to smell they must first inhale, and that they cannot do under [5] water.
Smells are of what is dry as flavours of what is moist. Consequently the organ of smell is potentially dry.
10 · What can be tasted is always something that can be touched, and just for that reason it cannot be perceived through an interposed foreign body, for no more is it so with touch. Further, the flavoured and tasteable body is suspended in a [10] liquid matter, and this is tangible. Hence, if we lived in water, we should perceive a sweet object introduced into the water, but the water would not be the medium through which we perceived; our perception would be due to the solution of the sweet substance in the water, just as if it were mixed with some drink. There is no parallel here to the perception of colour, which is due neither to any blending nor to [15] any efflux. In the case of taste, there is no medium; but as the object of sight is colour, so the object of taste is flavour. But nothing excites a perception of flavour without the help of liquid; what acts upon the sense of taste must be either actually or potentially liquid like what is saline; it must be both itself easily dissolved, and [20] capable of dissolving along with itself the tongue. Just as sight apprehends both what is visible and what is invisible (for darkness is invisible and yet is discriminated by sight; so is, in a different way, what is over-brilliant), and as hearing apprehends both sound and silence, of which the one is audible and the other [25] inaudible, and also over loud sound as sight does what is bright (for as a faint sound is inaudible, so in a sense is a loud or violent sound; and as one thing is called invisible absolutely (as in other cases of impossibility), another if it is adapted by nature to have the property but has not it or has it only in a very low degree, as when we say that something is footless or stoneless—so too taste has as its object both [30] what can be tasted and the tasteless—the latter in the sense of what has little flavour or a bad flavour or one destructive of taste. The primary difference seems to be that between what is drinkable and what is undrinkable—both are tasteable, but the latter is bad and tends to destroy taste, while the former is natural. What is drinkable is a common object of both touch and taste.