Concupiscentia, proprie loquendo, est in appetitu sensitivo, et in vi concupiscibili, quae ab ea denominatur, quia unicuique potentiae animae competit appetere proprium bonum appetitu naturali, qui non sequitur apprehensionem; sed appetere bonum appetitu animali, qui sequitur apprehensionem, pertinet solum ad vim appetitivam: appetere autem aliquid sub ratione boni delectabilis secundum sensum, quod proprie est concupiscere, pertinet ad vim concupiscibilem.
Properly speaking, concupiscence is in the sensitive appetite, and in its concupiscible power, which takes its name from it, because while it belongs to each power of the soul to seek its proper good by the natural appetite, which does not arise from apprehension, the craving for good, by the animal appetite, which arises from apprehension, belongs to the appetitive power alone: and to crave something under the formal aspect of a good that is delightful to the senses, wherein concupiscence properly consists, belongs to the concupiscible power.
Sicut philosophus dicit in I Rhetoric., concupiscentia est appetitus delectabilis. Est autem duplex delectatio, ut infra dicetur: una quae est in bono intelligibili, quod est bonum rationis; alia quae est in bono secundum sensum.
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 (q31, a3,a4): one is in the intelligible good, which is the good apprehended by formal aspect; the other is in good perceptible to the senses.
Prima quidem delectatio videtur esse animae tantum. Secunda autem est animae et corporis, quia sensus est virtus in organo corporeo; unde et bonum secundum sensum est bonum totius coniuncti. Talis autem delectationis appetitus videtur esse concupiscentia, quae simul pertineat et ad animam et ad corpus, ut ipsum nomen concupiscentiae sonat.
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 "con-cupiscentia." [="a together-desire"]