I answer that, As the Philosopher says (Rhet. i, 11), “concupiscence is a craving for that which is pleasant.”  Now pleasure is twofold, as we shall state later on (Q. 31, AA. 3, 4):  one is in the intelligible good, which is the good of reason; the other is in good perceptible to the senses.  The former pleasure seems to belong to soul alone:  whereas the latter belongs to both soul and body:  because the sense is a power seated in a bodily organ:  wherefore sensible good is the good of the whole composite.  Now concupiscence seems to be the craving for this latter pleasure, since it belongs to the united soul and body, as is implied by the Latin word “concupiscentia.”  Therefore, properly speaking, concupiscence is in the sensitive appetite, and in the concupiscible faculty, which takes its name from it.

Reply Obj. 1:  The craving for wisdom, or other spiritual goods, is sometimes called concupiscence; either by reason of a certain likeness; or on account of the craving in the higher part of the soul being so vehement that it overflows into the lower appetite, so that the latter also, in its own way, tends to the spiritual good, following the lead of the higher appetite, the result being that the body itself renders its service in spiritual matters, according to Ps. 83:3:  “My heart and my flesh have rejoiced in the living God.”

Reply Obj. 2:  Properly speaking, desire may be not only in the lower, but also in the higher appetite.  For it does not imply fellowship in craving, as concupiscence does; but simply movement towards the thing desired.

Reply Obj. 3:  It belongs to each power of the soul to seek its proper good by the natural appetite, which does not arise from apprehension.  But the craving for good, by the animal appetite, which arises from apprehension, belongs to the appetitive power alone.  And to crave a thing under the aspect of something delightful to the senses, wherein concupiscence properly consists, belongs to the concupiscible power. ________________________

SECOND ARTICLE [I-II, Q. 30, Art. 2]

Whether Concupiscence Is a Specific Passion?

Objection 1:  It would seem that concupiscence is not a specific passion of the concupiscible power.  For passions are distinguished by their objects.  But the object of the concupiscible power is something delightful to the senses; and this is also the object of concupiscence, as the Philosopher declares (Rhet. i, 11).  Therefore concupiscence is not a specific passion of the concupiscible faculty.

Obj. 2:  Further, Augustine says (QQ. 83, qu. 33) that “covetousness is the love of transitory things”:  so that it is not distinct from love.  But all specific passions are distinct from one another.  Therefore concupiscence is not a specific passion in the concupiscible faculty.