LECTIO SEVENTEEN

             § 451. After deciding about the origin of sound the Philosopher now comes to certain conclusions about sound's impression on sense: and first, at 'Hearing is etc.', about its effect on the sense-organ.

             First, then, he observes that, the medium of sound being air, it has been rightly said that the vacuum was an essential factor in hearing (for those who said this thought that 'the vacuum' was air). Now when air is disturbed it makes sound audible, provided that it is a single continuum such that a sound can be formed in it. For if sound is to be produced it requires a singleness and continuity in the air; therefore no sound occurs unless the sounding thing that is struck be smooth. A thing is smooth if no part of it juts out from the rest. A smooth surface, then, is a simple unity, upon which the air too exists in a single and uniform way. It is otherwise if the body in question has a rough surface; and since air is 'unstable', that is, easily broken up, it follows that neither will the air be a continuous unity, and therefore that no sound will be formed in it.

             § 452. It is clear then that nothing sounds, i.e. produces sound, unless it sets in motion a single continuum of air between itself and the hearing. It follows that those who said that the 'vacuum' was adapted to the sense of hearing said something to the point; for to be adapted to hearing is a property of air, which they called a 'vacuum'. But they were not right in using the term 'vacuum' for that which is really full of air.

             § 453. Then, when he says 'Hearing is naturally conjoined', he concludes about the impression made on hearing by sound, so far as the organ is concerned. And he does three things here. First, he shows that air is adapted to the organ of hearing: secondly, he shows what sort of air this is (at 'Of itself air'), and thirdly, he shows how hearing may or may not be obstructed by an impediment in the organ (at 'On this account therefore').

             First, then, he says that hearing has a natural congruity with air; air is adapted to the organ of hearing as watery fluid to the organ of sight. And this because, air pertaining to the organ of hearing, the same effect of sound can exist in the moving air both inside and outside the organ--the air inside acting as the instrument of hearing. This is why hearing does not occur in every part of the body, nor the sounding air produce a sound in, or penetrate into, every part of the animate body. The latter has not air in each of its parts so that any part might be set in motion by sound; in the same way as the living body has a certain watery fluid only in one special part (the pupil of the eye), not everywhere.

             § 454. Then, at 'Of itself air', he shows what sort of air is instrumental in hearing. And he says that everything that sounds is by nature resistant to percussion. Obviously air is not of itself a sounding material, for it does not by nature resist what strikes it, but rather yields easily. However, its yielding or diffusion can be prevented by a solid body, and then the movement of the air gives out a sound. For we have seen that, for the production of sound, two solids must strike against each other and against air. But the air proper to hearing is 'built into', or firmly set in, the ears with a certain stillness, in order that the animal may perceive distinctly every one of its movements. For, as the watery matter in the pupil lacks colour in order to take in all differences of colour, so must the air in the tympanum of the ear lack motion that it may discern every difference of sound.

             § 455. Next, at 'On this account', he shows how hearing may be hindered by an impediment in the organ. He states two impediments, according to the two conditions which, he says, are necessary to the organ of hearing. Of these, the first is air, and the second that this air be still. The first impediment, then, will be any elimination of the air. It follows therefore that hearing can take place in water, provided that the water does not penetrate to that special air which, as he says, is 'built into' the ear. But in fact water does not enter into the ear at all; because of the spirals which prevent its entry.

             § 456. But if water should happen to penetrate to this inner air, the animal would cease to hear, because the air needed for hearing would then have been eliminated; just as sight is prevented if the aqueous matter of the pupil is destroyed by the entry of some alien body. And not only is hearing impeded by the loss of this air, but also 'if the ear-drum', that is, the skin enclosing this air, or some adjoining portion, 'is ailing'; just as in the case of sight, when the cornea of the pupil which holds the aqueous matter of the eye is injured.

             § 457. Now, certain books maintain that we do not hear in water. This is contrary to what has been said here (that we hear both in air and in water) and also to what the Philosopher says in the Historia Animalium, that animals hear in water. For though the water does not penetrate to the interior air, it can set it in motion, and thus impress upon it some sort of sound.

             § 458. He states the second impediment to hearing at 'A test of good hearing'. This impediment would come from a lack of stability in the air of the inner ear: so he says that a sign of one's good or bad hearing is whether one continually hears a ringing in the ear, like the sound heard when a horn is held up to the ear; which sound is due to the movement of air in the horn. One in this condition has poor hearing, for the air in his ears is continually moving by a motion of its own. Each sound ought to be adventitious to the organ of hearing, not intrinsic; just as the organ of sight should receive each colour from without, having none of its own. If it has any of its own, sight is impeded. And in the same way, if the air in the ear has a motion and sound of its own, hearing is impeded. And it is because hearing thus comes about through air that some (thinking that air is a vacuum) say that we hear through a 'resounding vacuum'; and indeed the organ by which we hear has its own special, motionless air, quite distinct from the air outside.

             § 459. Then, at 'Is it that which strikes', he raises a question about the origin of sound: whether the active cause of sound is the thing that strikes or that which is struck. He concludes that both are causes, though in different ways; because as sound follows upon motion, whatever is an efficient cause of motion is so also of sound. Sound originates in the movement with which a thing striking rebounds from the resistance of the thing struck; just as 'bouncing' or resilient bodies rebound from hard smooth objects, when one impels them violently against the latter. Clearly then the thing striking is a cause of movement; and also the object struck, inasmuch as it makes the latter rebound: and thus both are efficient causes of the motion.

             § 460. And, because to produce sound it is necessary that there be a rebound from a struck thing's resistance, consequently not everything that strikes or is struck gives out sound (as was said to begin with): e.g. if one needle is struck against another. To produce sound what is struck must be 'smooth', that is, so disposed that the air spreads and moves at once when the thing struck resists. Such a movement will cause sound.

             § 461. Then, at 'Differences', he examines the differences of sounds. First, he shows how these differences are perceived; and secondly, how they are named (at 'These terms are used'). He says first, then, that different things produce different sounds. But these varieties in sounding bodies' capacity to produce sound are only manifested in act, not in potency. For as colours are not perceived without light, so high or low tones are not perceived until a sound is actual.

             § 462. Then, where he says 'These terms are used', he shows how differences of sound are named. And he does four things here. First, he states whence the names of sounds are taken, saying that they are taken by metaphor from tangible qualities; for obviously high and low are reckoned as tangible qualities.

             § 463. Next, at 'A high note moves', he explains these names, saying that a sound is 'high' which moves the sense of hearing much in a short time: while a 'low' sound is one which moves it little in a longer time.

             § 464. Thirdly, at 'But this does not mean' since the above descriptions would seem to apply to the fast and the slow (the fast being that which in a short time moves much, the slow that which in much time moves little), he shows how the high and low in sounds are related to the fast and slow in motions. The fast, he says, is not the same as the high-toned, nor the low-toned the same as the slow, any more than sound, differentiated by the high and the low, is the same as movement, differentiated by the fast and the slow. But, as movement causes sound, so speed of movement is the cause of high tones, and slowness of low; in the case of sounds caused by a single movement. But when sound is produced by many movements, it is frequency of movements that causes the high tones, whilst their slowness causes the low, as Boethius says in the De Musica. Hence the tauter is a string, the higher is its note; because at a single stroke it vibrates more frequently.

             § 465. Fourthly, at 'So there seems to be', he likens differences of sounds to the tangible qualities from which they are named: observing that these qualities do resemble the sharp or flat in sounds; for the high note 'pierces' the hearing, in that it disturbs it quickly; whilst the low tone 'thuds' on it, so to speak, because it takes a longer time to disturb it. So the one takes place rapidly, the other slowly. Concluding, he says that he has sufficiently examined sound.

420b 5-421a 6

VOICE

             VOICE is the sound of a living thing, no inanimate being utters voice, though, by analogy, the flute and the harp are said to 'speak'; and so, too, other inanimate objects which sound with duration, harmony and significance. The resemblance arises from voice also having these qualities.§§ 466-9

             Many animals have no voice, such as the bloodless, and, among those with blood, fish. And this is reasonable if, in fact, sound is a movement. But the fish that are said to have voice, such as those in the Achelous, make a sound through their gills, or in some other such way.§§ 470-1

             Voice is a sound made by an animal, but not from any part of its frame. Since all things sound by something striking another in a medium (which is air), it is reasonable that those only will have voice which inhale air.§ 472

             For Nature employs air inhaled for two operations; as it does the tongue for both taste and speech; of which one, taste, is a necessity; whence it exists in more species; while the other, self-expression, is for well-being. So with breath: it [regulates] interior heat--and this is necessary to existence, (the reason for this will be stated elsewhere); and it also serves voice, which is for well-being.§ 473

             Now the organ of respiration is the windpipe, and the purpose of this organ is to serve the lungs. Quadrupeds have more heat in this part than in others, so respiration is needed, and first of all around the heart. Hence it is necessary that air enter when [an animal] draws breath.§§ 474-5

             Hence a striking by the soul (in these parts) upon air inhaled through the windpipe is voice.§ 476

             For not every animal sound is voice, as we have said; there is clicking the tongue, and the noise made by coughing. There is needed a living being to utter the sound, and some accompanying phantasm. For voice is a significant sound; not that (merely) of air respired, as coughing is; rather, with it the air in the windpipe is struck against the windpipe.§ 477

             A sign of this is that we cannot produce voice while inhaling air nor while exhaling it, but only while retaining it. For what holds the air also sets it in motion. It is thus clear why fish have no voice; for they have no windpipe. They lack this member because they do not inhale air or breathe. Those who say otherwise are wrong. The cause of this, however, is another question.§ 478