as to the voice, it is deep in some animals, high in others, in others again well-pitched and in due proportion between both extremes. again, in some it is loud, in others small, and it differs in smoothness and roughness, flexibility and inflexibility. we must inquire then into the causes of each of these distinctions.

we must suppose then that the same cause is responsible for high and deep voices as for the change which they undergo in passing from youth to age. the voice is higher in all other animals when younger, but in cattle that of calves is deeper. we find the same thing also in the male and female sexes; in the other kinds of animals the voice of the female is higher than that of the male (this being especially plain in man, for nature has given this faculty to him in the highest degree because he alone of animals makes use of speech and the voice is the material of speech), but in cattle the opposite obtains, for the voice of cows is deeper than that of bulls.

now the purpose for which animals have a voice, and what is meant by ‘voice’ and by ‘sound’ generally, has been stated partly in the treatise on sensation, partly in that on the soul. but since lowness of voice depends on the movement of the air being slow and its highness on its being quick, there is a difficulty in knowing whether it is that which moves or that which is moved that is the cause of the slowness or quickness. for some say that what is much is moved slowly, what is little quickly, and that the quantity of the air is the cause of some animals having a deep and others a high voice. up to a certain point this is well said (for it seems to be rightly said in a general way that the depth depends on a certain amount of the air put in motion), but not altogether, for if this were true it would not be easy to speak both soft and deep at once, nor again both loud and high. again, the depth seems to belong to the nobler nature, and in songs the deep note is better than the high-pitched ones, the better lying in superiority, and depth of tone being a sort of superiority. but then depth and height in the voice are different from loudness and softness, and some high-voiced animals are loud-voiced, and in like manner some soft-voiced ones are deep-voiced, and the same applies to the tones lying between these extremes. and by what else can we define these (i mean loudness and softness of voice) except by the large and small amount of the air put in motion? if then height and depth are to be decided in accordance with the distinction postulated, the result will be that the same animals will be deep-and loud-voiced, and the same will be high-and not loud-voiced; but this is false.

the reason of the difficulty is that the words ‘great’ and ‘small’, ‘much’ and ‘little’ are used sometimes absolutely, sometimes relatively to one another. whether an animal has a great (or loud) voice depends on the air which is moved being much absolutely, whether it has a small voice depends on its being little absolutely; but whether they have a deep or high voice depends on their being thus differentiated in relation to one another. for if that which is moved surpass the strength of that which moves it, the air that is sent forth must go slowly; if the opposite, quickly. the strong, then, on account of their strength, sometimes move much air and make the movement slow, sometimes, having complete command over it, make the movement swift. on the same principle the weak either move too much air for their strength and so make the movement slow, or if they make it swift move but little because of their weakness.

these, then, are the reasons of these contrarieties, that neither are all young animals high-voiced nor all deep-voiced, nor are all the older, nor yet are the two sexes thus opposed, and again that not only the sick speak in a high voice but also those in good bodily condition, and, further, that as men verge on old age they become higher-voiced, though this age is opposite to that of youth.

most young animals, then, and most females set but little air in motion because of their want of power, and are consequently high-voiced, for a little air is carried along quickly, and in the voice what is quick is high. but in calves and cows, in the one case because of their age, in the other because of their female nature, the part by which they set the air in motion is not strong; at the same time they set a great quantity in motion and so are deep-voiced; for that which is borne along slowly is heavy, and much air is borne along slowly. and these animals set much in movement whereas the others set but little, because the vessel through which the breath is first borne has in them a large opening and necessarily sets much air in motion, whereas in the rest the air is better dispensed. as their age advances this part which moves the air gains more strength in each animal, so that they change into the opposite condition, the high-voiced becoming deeper-voiced than they were, and the deep-voiced higher-voiced, which is why bulls have a higher voice than calves and cows. now the strength of all animals is in their sinews, and so those in the prime of life are stronger, the young being weaker in the joints and sinews; moreover, in the young they are not yet tense, and in those now growing old the tension relaxes, wherefore both these ages are weak and powerless for movement. and bulls are particularly sinewy, even their hearts, and therefore that part by which they set the air in motion is in a tense state, like a sinewy string stretched tight. (that the heart of bulls is of such a nature is shown by the fact that a bone is actually found in some of them, and bones are naturally connected with sinew.)

all animals when castrated change to the female character, and utter a voice like that of the females because the sinewy strength in the principle of the voice is relaxed. this relaxation is just as if one should stretch a string and make it taut by hanging some weight on to it, as women do who weave at the loom, for they stretch the warp by attaching to it what are called ‘laiai’. for in this way are the testes attached to the seminal passages, and these again to the blood-vessel which takes its origin in the heart near the organ which sets the voice in motion. hence as the seminal passages change towards the age at which they are now able to secrete the semen, this part also changes along with them. as this changes, the voice again changes, more indeed in males, but the same thing happens in females too, only not so plainly, the result being what some call ‘bleating’ when the voice is uneven. after this it settles into the deep or high voice of the succeeding time of life. if the testes are removed the tension of the passages relaxes, as when the weight is taken off the string or the warp; as this relaxes, the organ which moves the voice is loosened in the same proportion. this, then, is the reason why the voice and the form generally changes to the female character in castrated animals; it is because the principle is relaxed upon which depends the tension of the body; not that, as some suppose, the testes are themselves a ganglion of many principles, but small changes are the causes of great ones, not per se but when it happens that a principle changes with them. for the principles, though small in size, are great in potency; this, indeed, is what is meant by a principle, that it is itself the cause of many things without anything else being higher than it for it to depend upon.

the heat or cold also of their habitat contributes to make some animals of such a character as to be deep-voiced, and others high-voiced. for hot breath being thick causes depth, cold breath being thin the opposite. this is clear also in pipe-playing, for if the breath of the performer is hotter, that is to say if it is expelled as by a groan, the note is deeper.

the cause of roughness and smoothness in the voice, and of all similar inequality, is that the part or organ through which the voice is conveyed is rough or smooth or generally even or uneven. this is plain when there is any moisture about the trachea or when it is roughened by any affection, for then the voice also becomes uneven.

flexibility depends on the softness or hardness of the organ, for what is soft can be regulated and assume any form, while what is hard cannot; thus the soft organ can utter a loud or a small note, and accordingly a high or a deep one, since it easily regulates the breath, becoming itself easily great or small. but hardness cannot be regulated.

let this be enough on all those points concerning the voice which have not been previously discussed in the treatise on sensation and in that on the soul.