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power of the soul desires some particular desirable thing--namely its own suitable object. Therefore, with regard to this object which is the desirable in general, we should not assign some particular power distinct from the others, called the appetitive power.
_On the contrary,_ The Philosopher distinguishes (De Anima ii, 3) the appetitive from the other powers. Damascene also (De Fide Orth. ii, 22) distinguishes the appetitive from the cognitive powers.
_I answer that,_ It is necessary to assign an appetitive power to the soul. To make this evident, we must observe that some inclination follows every form: for example, fire, by its form, is inclined to rise, and to generate its like. Now, the form is found to have a more perfect existence in those things which participate knowledge than in those 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 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 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. Nom. 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 be in them 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