Lecture 17 — High and low sounds and the medium of hearing

But a vacuum is rightly said to be proper to hearing—for air seems to be a vacuum. But this, when moved as a simple continuum, causes hearing.

On account of its instability, however, it gives no sound unless what is struck be smooth; then it has the required unity, holding together on account of the even surface, for the surface of a smooth thing is uniform. The sonorous, therefore, is that which moves a compact mass of air continuously as far as the organ of hearing.

Hearing is naturally conjoined with air; and because it is in air, therefore, by a movement in the air outside is caused an interior movement also. Hence an animal does not hear all over its body, nor does air penetrate everywhere. For the ensouled body and the part to be set in motion have not air throughout (as also there is liquid only in the pupil).

Of itself air is soundless, for, being mobile, it easily yields. But when its motion cannot be diffused, a sound arises. There is air built into the ears so as to be immobile; and it accordingly senses every variety of motion with exactitude.

On this account, therefore, we hear also in water, for this does not penetrate to that inner air, nor, by reason of its many convolutions, into the ear. Should it do so, one would not hear; nor would we hear if the eardrum were ailing—just as we do not see if the cornea of the pupil is diseased.

A test of good hearing, on the contrary, is whether there is a continual ringing in the ear, like a horn. For then the air in the ear is perpetually moving by a motion of its own, whereas sound is external and is not the ear’s own. And for this reason they say that we hear by a “resounding vacuum,” because we hear by what holds air in constraint.

Is it that which strikes, or that which is struck, which sounds? Or both, but in different ways? For sound is a movement of something that can move in the way that a bouncing body flies off a smooth surface one flings it at. As has been said, not everything that strikes or is struck gives a sound, for instance, one needle struck against another. But what is struck must have a plane surface smooth and regular so that the air rebound and be set in motion instantaneously.

Differences in sonorous things are apparent in the act of sounding. For just as colors are not seen without light, so there is no high or low note apart from sounding.

These terms are used by metaphor from things perceived by touch. (What are translated in the previous and subsequent paragraphs as “high” and “low” are more literally “sharp” and “heavy.” Hence the connection with touch is less obvious in our English idiom.)

A high note moves the sense organ much in a brief space of time; the low note, little, in a longer time.

But this does not mean that the fast is the high and the slow the low; rather, the former arises because of swiftness of motion, the latter because of slowness.

So there seems to be an analogy with the tangible, as sharp and blunt. For the sharp pierces, while the blunt thuds; and the reason is that the one moves in a brief period, the other in a greater. Hence it comes about that the former is swift, but the latter is slow.

Let this serve to determine sound.

451. But a vacuum is rightly said (419b33). After deciding about the generation of sound, the Philosopher now comes to certain conclusions about sound’s impression on sense:

and first, inasmuch as it is an impression on a medium;

and second, at hearing is (420a4; [453]), inasmuch as it is an impression on the instrument or organ of sense.

First, then, he observes that, the medium of sound being air, it has been rightly said that a vacuum is proper to hearing (because to them air seems to be a vacuum). Now, when air is moved, it causes hearing, provided that it is a simple 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, that is, produces sound, unless it sets in motion the air continuously as far as the organ of 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 (420a4), he concludes about the impression made on hearing by sound, insofar as the organ of hearing is concerned. And he does three things here.

First, he shows that air is adapted to the organ of hearing:

second, he shows what sort of air this is, at of itself air (420a7; [454]);

third, he shows how hearing may or may not be obstructed by an impediment in the organ, at on this account therefore (420a11; [455]).

First, then, he says that hearing is naturally conjoined with air; air is adapted to the organ of hearing as watery fluid to the organ of sight. And this is because, since air pertains to the organ of hearing, the same effect of sound can exist in the moving outside the organ and in the air inside that is moved as the instrument of hearing. This is why the animal does not hear in every part of the body, nor the sounding air produce a sound in, or penetrate, every part of the ensouled body. The ensouled body 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 ensouled body has a certain watery liquid only in one special part (the pupil of the eye), not everywhere.

454. Then, at of itself air (420a7), 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. (Lect. 16, n. 442.)

But the air connatural to hearing is built into, or firmly set in, the ears, so as to be immobile, in order that the animal may sense distinctly every variety of motion. For as the watery matter in the pupil lacks every color in order to know all differences of color, so must the air in the tympanum of the ear lack every motion so that it may discern all the differences of sound.

455. Next, at on this account (420a11), 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 we hear in water, provided that the water does not penetrate to that inner air which, as he says, is built into the ear. But in fact water does not penetrate into the ear at all; this is impossible because of its convolutions, 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 eardrum, 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. (Cf. Peter of Spain, Expositio Lib. II–III De anima; Anonymous, Qu. in tres libros De anima, q. 48, a. 3.) This is contrary to what has been said here (that we hear both in air and in water) (2.8, 419b18.) and also to what the Philosopher says in the History of Animals, that animals hear in water. (Aristotle, History of Animals 4.8, 533b4–534a11.) 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 (420a15). 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 perpetually moving by a motion of its own. Each sound ought to be external to the organ of hearing, not intrinsic, just as the organ of sight should receive each color 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 for this reason, that hearing thus comes about through air, that they (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 constrained air, immobile and distinct from the air outside.

459. Then, at is it that which strikes (420a19), he raises a question about the generation 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 flings 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: for example, if one needle is struck against another. (Lect. 16, nn. 443–44.) To produce sound, what is struck must be smooth, that is, so disposed that the air be set in motion instantaneously when the thing struck resists. Such a movement will cause sound.

461. Then, at differences (420a26), he examines the differences of sounds.

First, he shows how these differences are perceived;

and second, how they are named, at these terms are used (420a29; [462]).

He says first, then, that different things produce different sounds. But these differences in sonorous things’ capacity to produce sound are only manifested in act, not in potency. For just as colors are not seen without light, so high or low tones are not perceived until a sound is actual.

462. Then, where he says, these terms are used (420a29), 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 used by metaphor from tangible qualities; for obviously high and low (Literally, “sharp” and “heavy.”) are counted among the tangible qualities.

463. Second, at a high note moves (420a30), he explains these names, saying that a sound is high which moves the sense of hearing much in a brief space of time; while a low sound is one which moves it little in a longer time.

464. Third, at but this does not mean (420a31), since the above descriptions would seem to apply to the fast and the slow (the fast being that which in a short time is moved much, the slow that which in much time is moved 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 movement is the cause of low. But this is understood in the case of sounds caused by a single movement; when sound is produced by many movements, it is frequency of movements that causes the high tones, while their slowness causes the low, as Boethius says in the De musica. (Boethius, De institutione musica, bk. 1, ch. 3, nn. 23ff; ch. 8, nn. 6–10.) Hence the more taut a string is, the higher is its note, because at a single stroke it vibrates more frequently.

465. Fourth, at so there seems to be (420b1), he likens differences of sounds to the tangible qualities from which they are named, observing that there seems to be an analogy with the tangible, as sharp and blunt in sounds; for the high note pierces the hearing, in that one moves in a brief time; while the low tone thuds on it, because it takes a greater time to disturb it. So the one comes about rapidly, the other slowly. Concluding, he says that he has sufficiently examined sound.