Natural and elicited appetite.
Appetite is the traditional name for what modern psychology calls the force of conation, orexis, or motivation. In the broadest sense, appetite means any tendency of a thing to an object. In cosmology, we said that the essential feature of material beings is motion. A certain motion follows every material being. Even more, we know that the form is the principle of operation because it is act. St. Thomas says that some inclination follows every form. (ST I, 80, 1.) This inclination is called natural appetite. This inclination is always the same, because the form does not change and the inclination is a consequence of the mere existence of the form, e.g., gravity follows the form of heavy bodies.
In opposition to natural appetite, there exists the so-called elicited appetite, i.e., an inclination called forth by an act of cognition. Aquinas summarizes in this remarkable way the nature of these two appetites: The form is found to have a more perfect existence in these things which participate knowledge than in those things which lack knowledge. For in those which lack knowledge, the form is found to determine each thing only to its own being– that is, to its nature. Therefore this natural form is followed by a natural inclination, which is called the natural appetite. But in those things which have knowledge, each one is determined to its own natural being by its natural form, in such a manner that it is nevertheless receptive of the species (forms) of other things: for example, sense receives the species of all things sensible, and the intellect, of all things intelligible, so that the soul of a man is, in a way, all things by sense and intellect: and thereby, those things that have knowledge, in a way, approach to a likeness to God, “in whom all things pre-exist,” as Dionysius says (Div. Names, V).
Therefore, as forms exist in those things that have knowledge in a higher manner and above the manner of natural forms; so must there by an inclination surpassing the natural inclination, which is called the natural appetite. And this superior inclination belongs to the appetitive power of the soul, through which the animal is able to desire what it apprehends, and not only that to which it is inclined by its natural form. And so it is necessary to assign an appetitive power to the soul.ST I, 80, 1.
If the knowledge is intellectual knowledge, the appetite is intellectual, and is called the will. If the knowledge is sense knowledge, the appetite will be sense appetite, a tendency towards the good which is apprehended by the sense. It is called passion.
The appetite elicited by cognition is to be distinguished from the natural appetite of any potency. But the appetitive potencies possess both appetites. For example, the will, as a natural appetite, necessarily seeks the good, any good. The will, as a power which depends on the apprehension of the intellect, may choose this particular good or that one. It is thus an elicited appetite. We strive for happiness necessarily (by nature), but not for this or that happiness.
The existence of appetite.
The existence of appetite may be recognized through internal experience (introspection) and external experience. Through internal experience, we recognize the existence of motions which are consequent to our knowledge. Through external experience, we see human beings and animals as inclined towards objects they know, or as inclined to avoid them. We must remember that knowledge is the acquisition of forms, of perfections. A motion follows the apprehension of these forms as the cognitive power judges them to be convenient or harmful for the animal. The movement of the appetite towards a particular object or away from it follows immediately upon this judgment.
Knowledge and appetite compared.
Knowledge and appetite differ in various ways.
- Knowledge perfects the cognitive powers. The object known is in the power according to the nature of the power, namely, in an immaterial way (immaterialiter). The term of knowledge is the intellect or the senses themselves. The formality of knowledge is the truth.
- The object of the appetite, however, is the object as it exists in nature. The term of appetite is the real object, not the object as it exists in our mind. Its formality is not the truth, but the good.
- The appetitive power follows upon the cognitive power. The elicited appetite is a passive potency in the sense that it needs to be determined to its action by the good apprehended by a cognitive potency.
Formal ratio of the appetite.
The formality of the appetite is the good. The appetite cannot desire evil as such, unless evil is apprehended under the formality of good (i.e., as an apparent good). The appetite not only tends towards the good, but also avoids evil. Thus there exists a double motion in every appetite, of attraction towards the good and repulsion from evil.