Reply Obj. 1:  The same thing that is the object of the natural appetite, may be the object of the animal appetite, once it is apprehended.  And in this way there may be an animal concupiscence of food, drink, and the like, which are objects of the natural appetite.

Reply Obj. 2:  The difference between those concupiscences that are natural and those that are not, is not merely a material difference; it is also, in a way, formal, in so far as it arises from a difference in the active object.  Now the object of the appetite is the apprehended good.  Hence diversity of the active object follows from diversity of apprehension:  according as a thing is apprehended as suitable, either by absolute apprehension, whence arise natural concupiscences, which the Philosopher calls “irrational” (Rhet. i, 11); or by apprehension together with deliberation, whence arise those concupiscences that are not natural, and which for this very reason the Philosopher calls “rational” (Rhet. i, 11).

Reply Obj. 3:  Man has not only universal reason, pertaining to the intellectual faculty; but also particular reason pertaining to the sensitive faculty, as stated in the First Part (Q. 78, A. 4; Q. 81, A. 3):  so that even rational concupiscence may pertain to the sensitive appetite.  Moreover the sensitive appetite can be moved by the universal reason also, through the medium of the particular imagination. ________________________

FOURTH ARTICLE [I-II, Q. 30, Art. 4]

Whether Concupiscence Is Infinite?

Objection 1:  It would seem that concupiscence is not infinite.  For the object of concupiscence is good, which has the aspect of an end.  But where there is infinity there is no end (Metaph. ii, 2).  Therefore concupiscence cannot be infinite.

Obj. 2:  Further, concupiscence is of the fitting good, since it proceeds from love.  But the infinite is without proportion, and therefore unfitting.  Therefore concupiscence cannot be infinite.

Obj. 3:  Further, there is no passing through infinite things:  and thus there is no reaching an ultimate term in them.  But the subject of concupiscence is not delighted until he attain the ultimate term.  Therefore, if concupiscence were infinite, no delight would ever ensue.

On the contrary, The Philosopher says (Polit. i, 3) that “since concupiscence is infinite, men desire an infinite number of things.”

I answer that, As stated above (A. 3), concupiscence is twofold; one is natural, the other is not natural.  Natural concupiscence cannot be actually infinite:  because it is of that which nature requires; and nature ever tends to something finite and fixed.  Hence man never desires infinite meat, or infinite drink.  But just as in nature there is potential successive infinity, so can this kind of concupiscence be infinite successively; so that, for instance, after getting food, a man may desire food yet again; and so of anything else that nature requires:  because these bodily goods, when obtained, do not last for ever, but fail.  Hence Our Lord said to the woman of Samaria (John 4:13):  “Whosoever drinketh of this water, shall thirst again.”