Thomas Aquinas, Disputed Questions on Truth (De Veritate)

1. The powers of the soul are ordained only to vital operations. Now those operations are called vital by which animate things are distinguished from inanimate. But it is not as regards tending that animate things are distinguished from inanimate, because even the inanimate tend to good. Appetite is therefore not a special power of the soul.

2. Appetite is nothing, it seems, but a sort of direction to an end. But natural appetite suffices for a thing to be directed to an end. So there is no necessity of adding an animal appetite which would be a special power of the soul.

3. Operations and powers are differentiated as to their terms. But there is the same term, good, for both natural and animal appetite. It is therefore the same power or operation. But natural appetite is not a power of the soul. Then neither is animal appetite.

4. Appetite is for what is not had, according to Augustine. But in the case of animals the good is already had by knowledge. Therefore there does not follow upon knowledge among animals any appetite which would call for a special power.

5. A special power is destined for a special act, not for an act common to all the powers of the soul. But to tend to good is common to all the powers of the soul. This is apparent from the fact that every power tends to its object and takes pleasure in it. Therefore appetite is not a special power of the soul.

6. If the appetitive power tends to good, it tends either to good in general or to what is good for itself. Now if it should tend to good in general, since every other power tends to some particular good, the appetitive power will not be a special power but a universal one. But if it tends to what is good for itself, since every other power also tends to what is good for itself, every other power can for the same reason be called an appetite. There will therefore not be any power of the soul which can be called appetite in a special way.

To the Contrary:

The Philosopher posits the appetitive part as a special power of the soul.

REPLY:

Appetite is a special power of the soul. In this regard it should be noted that, since the powers of the soul are destined for operations proper to animate beings, an operation has a special power of the soul appointed for it for the reason that it is an operation proper to an animate being. There is found, indeed, a certain operation which from one point of view is common to both animate and inanimate beings but from another is proper to animate beings; for instance, to be moved or generated.

Spiritual things considered in themselves have such a nature as to move but not to be moved. Bodies, however, are moved; and though one can move another, still no one of them can move itself. For things which move themselves are divided into two parts, one of which is the mover, the other, moved, as is shown in the Physics.

But this cannot be realized in purely corporeal beings, because their forms cannot be movers, though they can be the principle of motion in the sense of that by which something is moved. In the movement of the element earth, for instance, heaviness is the principle by which it is moved but yet is not the mover. This is so both because of the simplicity of inanimate bodies, which do not have enough diversity in their parts for one to originate motion and another to be moved, and also because of the baseness and materiality of their forms, which, being far removed from the separated forms to which it belongs to move, do not retain the ability to move but only the function of being principles of motion.

Animate things, however, are composed of a spiritual and a corporeal nature. There can accordingly be in them a moving part and another moved--both locally and in other ways. And so, inasmuch as to be moved is made an action proper to animate beings in the sense that they move themselves to definite species of movement, there is found in animals a hierarchy of special powers. Thus for locomotion in animals there is a motive power; and in plants and animals alike, a power of growth for the movement of growing, a nutritive power for the movement of alteration, and a generative power for the movement of generation. To tend, which is in a way common to all things, likewise becomes in a way special for animate beings, or rather animals, inasmuch as there are found in them appetite and what moves the appetite. This latter, according to the Philosopher, is the apprehended good itself. Hence, just as animals more than other things are moved of themselves, so too they tend of themselves. For this reason the appetitive power is a special faculty in the soul in the same way as the motive power.

Answers to Difficulties:

1. The solution is clear from what has already been said.*

2. It is precisely because animals are capable of participating in divine goodness in a more eminent way than other, inferior things, that they have need of many operations and helps to their perfection. A man who can gain perfect health by much exercise is nearer to health than one who can attain only a little health and needs for this only a little exercise--to use the example given by the Philosopher. Now a natural appetite is determined to a single object and cannot be so diversely oriented that it extends to as many different things as animals have need of. For this reason it was necessary for animals to be supplied in addition with an animal appetite consequent upon apprehension so that among many objects of apprehension the animal would be attracted to different ones.

3. Although good is sought by both natural and animal appetite, nevertheless by its natural appetite a thing does not of itself seek good as it does by its animal appetite. Consequently for the seeking of good by animal appetite there is required a power which is not required for the exercise of natural appetite. Furthermore the good to which a natural appetite tends is definite and always the same; but this is not true of the good sought by an animal appetite. And the same can be applied to the motive power.

4. The being which desires a good does not seek to have the good according to its intentional existence, as it is had by one who knows it, but according to its essential or real existence. Consequently the fact that an animal possesses the good by knowing it does not keep it from being able to desire it.

5. Every power tends to its object by a natural appetite. But animal appetite belongs to a special power. And because natural appetite is determined to a single object whereas animal appetite follows apprehension, individual powers tend to a determined good but the appetitive faculty tends to any good apprehended. Yet it does not follow that it is a universal power, since it tends to good in a special way.

6. The solution to this difficulty is evident from what has just been said.