Whether a power regulating life exists in a human.
One inquires further whether a power regulating life exists in a human.
1. It seems not. For a human is not ruled in only one operation, but in diverse operations. But there is no single power in the human which can rule all his operations; therefore, etc.
2. Moreover, a regimen corresponds to life. Therefore, whatever gives life, gives the regimen. But form is the principle of life, and therefore, it is the principle of the regimen. Therefore, it is not necessary to posit a regulative power beyond the form itself.
3. Moreover, if there is such a power, it will either be a vital, natural, or animal power. But none of these can be [the regulative power] because no one of them can have dominion over another. Therefore, etc.
To the contrary. That one seems to be a regulative power of life which all the others presuppose and which does not itself presuppose another. But the vital power is one like this; therefore, etc.
Yet it seems to be the natural power. Because that seems to be the regulative power which attracts what is suitable and which expels what is noxious. But the natural power is one like this, and therefore, etc.
Yet it seems to be the animal power. Because an animal is distinguished from a non-animal by sensation and motion. But the animal power confers sensation and motion, and therefore, etc.
One must respond that in an animal (or in the human) there is some power that is regulative of life because certain parts exist in the animal that are opposed to one another. For, unless it is blocked, the natural heat has to consume the radical moisture in which it exists as if in a subject, but it does not consume the moisture itself. And this will only be the case if it is ruled by some power.
Moreover, each power in an animal follows its proper function, as it is born to do, which will only be the case if there is some power in the animal that is regulative of life itself.
But doubt exists as to what the regulative power is, and this quite commonly is doubted by a great number of physicians in various places. For some say that it is one power formed into a whole out of all the other powers, and others say that it is one common power that is distinct from the others.
Nevertheless, it seems to me that one should respond that it is not one power, but several, and these are the natural, the vital, and the animal. Life is not ruled sufficiently by any one of these apart from the others, but rather each of these is required for a complete regimen, and each in some way rules another. For it is saidand it sounds extraordinary, although it may be part of nature [licet sit physicum]that an offspring often resembles what the woman imagines or what falls into her imagination at conception. In this way, Avicenna says, a certain woman, owing to this, gave birth to a dwarf. But this would only be the case if the imaginative power ruled the generative power in some way, and so too for the others. In truth, just as the heart is the principal part in the animal, so too can the vital power, which is immediately situated in the heart, be called principal and regulative with respect to the others because a more noble power and operation is due to the more noble member and because without heat, which proceeds from the heart, no other power can operate adequately.
The arguments prove that there is not just one power in the animal that is sufficient, without the others, to regulate life.
To the second argument one can respond that in no [principle] beyond the first is the substance of something also its operation. Thus the soul is not the immediate principle of its operation except through an intermediary that is the power or potency, just as one must see in the book On the Soul and as we have explained there. Thus if life is received on behalf of the first act, the soul is its immediate principle; if it is received on behalf of the second, then the soul is not the principle of life except as a mediating power.