Whether voice is natural or voluntary or artificial.
"Voice," etc. Here one asks about voice. And first, one asks whether voice, or the generation of voice, is natural or voluntary or artificial.
1. It seems that it is not natural. We cannot accelerate a natural operation, but we can accelerate or retard the formation of voice; therefore, this is not natural.
2. Moreover, "what is natural is the same for all," according to Boethius's On Division. But the formation of voice is not the same in all, and therefore, etc.
3. Moreover, a man and a boy have the same nature. If, therefore, the formation of voice were natural, then boys would give voice in the same way as men, which is false, and therefore, etc.
To the contrary. The effect of a natural potency is a natural effect. But the vocative potency is natural, seeing that its instruments are natural.
Moreover, the tongue is suited for two tasks according to the Philosopher in the second book of On the Soul: to wit, taste and speech. But taste is a natural operation, and therefore, so too is speech.
One must reply to this that the formation of voice can be related to the instruments by whose mediation it occurs (think of the power of the heart and the lungs and the arteries and the tongue and the palate and the teeth), and thus it is itself natural because a natural operation proceeds with a natural instrument mediating.
In another way it can be related to the animal powers commanding the aforementioned powers, for example, to the will (whether to the rational appetite in a human and the concupiscent appetite in a brute beast) and in this way the formation of voice can be called voluntary, for it is in the human to form voice. For even though he has the instruments or principles of voice, he can nevertheless desist from the formation of voice.
Third, the formation of voice can be related to an accidental variation in the voice. And in this way the formation of voice is artificial insofar as it is up to the will of different individuals who, for the sake of expressing different concepts, form different voices. Seen this way, the Philosopher speaks for the first [solution when he says] that voice is by nature and is shared by all. But the Philosopher speaks for the last [solution when he says] that speech is not natural because speech properly adds articulation and order to voice.
Thus, briefly one can say that insofar as voice is a sound emitted by an animal in order to express a concept, namely, of joy or sadness, it is natural. Insofar as it is an articulate and ordered sound, it is artificial and conventional. And for this reason one is accustomed to say that speech is from nature, but speaking in this or that manner is conventional.
1. Through this one can respond to the arguments. To the first, one should reply that because the operations of vital parts obey the appetite with respect to movement, and since the formation of voice occurs in many with the mediation of appetite, then an animal can retard or speed its voice according to what it desires.
2. To the second argument one must reply that although an ordered, articulate, and signifying voice is not the same among all, the initial formation is nevertheless the same among all as far as the natural instruments are concerned. Thus all people give voice in the same way although they do not speak in the same way.
3. To the third argument one must reply that the vocative power is active, and in children the active power is weak and the operative instruments are weak, and this is why a boy cannot give voice like a man.
Arguments to the contrary proceed in the same fashion.
Whether every voice is significative.
Next one asks whether every voice is significative.
1. And it seems so. Voice is the striking upon the windpipe [vocalis arteria] by air that has been breathed in by the soul or by a power that is in these parts, and accompanied by an image being signified. But every utterance with an image being signified is significative; therefore, etc.
2. Moreover, just as speech is varied in humans, so also there is a voice that is varied in animals, like mooing in a cow and a horse's whinny and a sheep's bleating or baaing and a dog's barking, etc. But every speech is significative. For Plato says that words were invented just for this purpose, to give an immediate indication of a shared desire. Therefore, every voice is significative.
3. Moreover, voice is something sensible to the hearing that is present in animals, so that they may apprehend shared concepts. But this cannot occur unless voice is significative. Therefore, since art, like nature, does nothing in vain, every voice whether natural or artificialwill be significative.
To the contrary. Every voice signifies either by imposition or by nature. But there is a certain voice that is neither imposed significatively on a thing nor represents something naturally. Therefore, not every voice is significative.
Besides, the thing's intention is in the soul. If then the voice is imposed on it, then the intention is either wholly in the soul or wholly in the imposed voice, or is in both. If it is wholly in the one so that it is not in the other, this [intention] cannot be in the voice as long as it is not in the soul. It is therefore necessary that what is not in the voice be in the soul. It cannot be in both, because then the same thing would be in different things.
It must be said that voice can be informed in two ways, because there is a vocative power in its formation which can be informed by the estimative or imaginative power, just as occurs in clever animals, or it can be by means of reason, as is the case for the human, and this is for the sake of expressing something. And the voice formed in this way is significative because such voice is a sign of an internal concept.
It can also be considered in another way, insofar as the vocative power is not governed by an animal power, and in this way not every voice is significative because a human can form many things and vocalize them by accident, not for the sake of expressing anything at all. He rather forms or fashions various voices in response to a joke or jest, and voices of this sort are not significative. Nevertheless, something like this is not a voice without being able to be imposed on a thing to be signified.
1. On to the arguments. To the first, one must respond that the Philosopher speaks of a voice which is made by nature and is governed by imagination, and such voice is significative. For although it is not significative of something outside the sign, it is nevertheless a sign of its own previously imagined thing, and voice is nevertheless a sign in the utterance because it was imagined thus.
2. To the second argument one must say that although words were invented for the sake of giving expression to concepts, not all words express determinate concepts, and this is why they lack a proper end.
3. One must respond to the third argument in the same way.
-  On vocalis arteria as "windpipe," cf. DA 18.104.22.168 (SZ 1: 774-75).