Plotino – Tratado 29,5 (IV, 5, 5) — A Audição

5. En cuanto a la acción de oír, hemos de preguntarnos si es el aire el afectado y si, por ejemplo, el aire situado al lado del cuerpo recibe el primer impulso del cuerpo sonoro, impulso que se transmitirá hasta el oído para culminar en la sensación. Porque podríamos suponer que el medio resulta afectado por accidente, por encontrarse entre el cuerpo sonoro y el oído, con lo cual, si se suprime el medio una vez producido el sonido, como, por ejemplo, a raíz del choque de dos cuerpos, la sensación no llegaría de modo inmediato hasta nosotros.

Conviene, pues, que primeramente sea golpeado el aire, pero no en absoluto el aire intermedio entre el cuerpo sonoro y el oído. Porque parece evidente que el aire próximo al cuerpo sonoro es el principio del sonido, ya que nunca se produciría éste por el choque de dos cuerpos, si el aire, golpeado y rechazado por ellos en su rápido encuentro, no devolviese a su vez el golpe, transmitiendo así este choque al aire cercano a los oídos. Ahora bien, si el aire, y el choque que resulta de su movimiento, es el principio del sonido, ¿cómo se producen las diferencias entre las voces y los sonidos? El bronce resuena de manera diferente, según golpee el bronce u otro cuerpo. Y otro tanto ocurre con los demás cuerpos. Pero el aire, en cambio, es sólo uno y lo mismo el golpe que recibe, mientras que los sonidos no se diferencian únicamente por su magnitud y su pequeñez.

Digamos, en fin, que si el aire produce el sonido al golpear un cuerpo, no lo produce realmente como tal aire. Porque, para producir un sonido, el aire debería mantenerse estable como un cuerpo sólido, permaneciendo también como algo sólido antes de difundirse. Basta, por consiguiente, con el choque de dos cuerpos, pues la misma conmoción que esto produce hiere nuestros sentidos y origina el sonido. Lo prueban igualmente los sonidos que se producen en el interior de los animales, que no son debidos al aire, sino que son originados por el choque mutuo de unas partes con otras. Así, por ejemplo, cuando se pliegan las articulaciones, los huesos frotan unos con otros y se les oye rechinar sin que medie entre ellos el aire. Estas son las dificultades relativas al oído, semejantes a las que conciernen a la vista. Al igual que se decía entonces, la impresión del oído supone también una cierta simpatía en el ser animado.

V. Faut-il admettre que, pour l’ouïe, l’air est d’abord mis en mouvement, puis que, ce mouvement se transmettant de proche en proche et sans altération depuis l’air qui produit le son jusqu’à l’oreille, le son arrive ainsi jusqu’au sens ? Ou bien le milieu est-il affecté ici par accident, et seulement parce qu’il est interposé, de telle sorte que, si le milieu était anéanti, une fois que le son serait produit par le choc de deux corps, nous le sentirions aussitôt? — II faut que l’air soit d’abord mis en mouvement, mais le milieu qui 418 est interposé [entre l’air mis d’abord en mouvement et l’oreille] remplit un autre rôle. L’air paraît être ici la condition souveraine de la production du son : car, dans l’origine, le choc de deux corps ne produirait pas de son, si l’air, comprimé et frappé par leur rencontre rapide, ne transmettait de proche en proche le mouvement jusqu’à l’oreille (15). Mais, si la production du son dépend des impulsions imprimées à l’air, il reste à expliquer les différences des voix et des sons : car, autre est le son que rend l’airain quand il est frappé par l’airain, autre le son qu’il rend quand il est frappé par un autre métal, etc. Cependant l’air est un ainsi que l’impulsion qu’il reçoit [pour produire le son] , et les différences que nous considérons ne consistent pas simplement en plus et en moins. Si l’on rapporte à l’air la production de la voix et du son (16), parce que l’impulsion imprimée à l’air est sonore, nous ferons observer que l’air n’est pas la 419 cause du son en tant qu’air : car il ne résonne qu’autant qu’il ressemble à un corps solide, demeurant en place, avant de se dilater, comme quelque chose de solide (17). Il suffit donc ici des objets qui se choquent, et ce choc ou cette impulsion forme le son qui parvient au sens de l’ouïe. On en a une preuve dans les sons qui se produisent à l’intérieur des animaux, sans air; quand une partie est frappée par une autre : tel est le son que rendent certaines articulations, quand on les fléchit, ou certains os, quand on les choque l’un contre l’autre ou qu’on les brise ; dans ce cas, l’air n’intervient pas.

Telles sont les considérations auxquelles l’ouïe donne lieu, et qui ressemblent à celles auxquelles nous nous sommes livrés au sujet de la vue. Il faut donc dire; pour l’ouïe, que sa perception consiste, comme celle de la vue, en une affection ressentie sympathiquement dans l’animal universel.

NEITHER FOR HEARING IS THE AIR NECESSARY AS A MEDIUM.

5. As to hearing, there are several theories. One is that the air is first set in motion, and that this motion, being transmitted unaltered from point to point from the (location of the) sound-producing air as far as the ear, causes the sound to arrive to the sense. Again, another theory is that the medium is here affected accidentally, and only because it happens to be interposed; so that, if the medium were annihilated, we would feel the sound immediately on its production by the shock of two bodies. We might think that the air must first be set in motion, but the medium interposed (between the first moved air and the ear) plays a different part. The air here seems to be the sovereign condition of the production of sound; for, at the origin of the sound, the shock of two bodies would produce no sound if the air, compressed and struck by their rapid concussion did not transmit the motion from point to point as far as the ear. But if the production of the sound depend on the impulsion impressed on the air, the (qualitative) difference between voices and (instrumental) sounds will challenge explanation; for there is great difference (of “timbre”) between metal struck by metal of the same kind, or another. These differences are not merely quantitative, and cannot be attributed to the air which (everywhere) is the same, nor to the force of the stimulus (which may be equal in intensity). Another theory (of Aristotle’s) is that the production of voices and sound is due to the air, because the impulsion impressed on the air is sonorous. (To this it shoud be answered that) air, in so far as it is air, is not the cause of sound; for it resounds only in so far as it resembles some solid body, remaining in its situation, before it dilates, as if it were something solid. The (cause of the sound) then is the shock between objects, which forms the sound that reaches the sense of hearing. This is demonstrated by the sounds produced in the interior of animals, without the presence of any air, whenever one part is struck by some other. Such is the sound produced by certain articulations when they are bent (as, the knee); or certain bones, when they are struck against each other, or when they break; in this case air has nothing to do with the production of the sound. These considerations compel a theory of hearing similar to our conclusions about sight. The perception of audition, like that of vision, therefore consists in a repercussion (an affection sympathetically felt) in the universal organism.

5. But some doubt arises when we consider the phenomena of hearing.

Perhaps we are to understand the process thus: the air is modified by the first movement; layer by layer it is successively acted upon by the object causing the sound: it finally impinges in that modified form upon the sense, the entire progression being governed by the fact that all the air from starting point to hearing point is similarly affected.

Perhaps, on the other hand, the intervenient is modified only by the accident of its midway position, so that, failing any intervenient, whatsoever sound two bodies in clash might make would impinge without medium upon our sense?

Still air is necessary; there could be no sound in the absence of the air set vibrating in the first movement, however different be the case with the intervenient from that onwards to the perception point.

The air would thus appear to be the dominant in the production of sound: two bodies would clash without even an incipient sound, but that the air, struck in their rapid meeting and hurled outward, passes on the movement successively till it reaches the ears and the sense of hearing.

But if the determinant is the air, and the impression is simply of air-movements, what accounts for the differences among voices and other sounds? The sound of bronze against bronze is different from that of bronze against some other substance: and so on; the air and its vibration remain the one thing, yet the difference in sounds is much more than a matter of greater or less intensity.

If we decide that sound is caused by a percussion upon the air, then obviously nothing turning upon the distinctive nature of air is in question: it sounds at a moment in which it is simply a solid body, until [by its distinctive character] it is sent pulsing outwards: thus air in itself is not essential to the production of sound; all is done by clashing solids as they meet and that percussion, reaching the sense, is the sound. This is shown also by the sounds formed within living beings not in air but by the friction of parts; for example, the grinding of teeth and the crunching of bones against each other in the bending of the body, cases in which the air does not intervene.

But all this may now be left over; we are brought to the same conclusion as in the case of sight; the phenomena of hearing arise similarly in a certain co-sensitiveness inherent in a living whole.