Reply Obj. 1: Hope and memory are indeed of things which, absolutely speaking, are absent: and yet those are, after a fashion, present, i.e. either according to apprehension only; or according to apprehension and possibility, at least supposed, of attainment.
Reply Obj. 2: Nothing prevents the same thing, in different ways, being the cause of contraries. And so hope, inasmuch as it implies a present appraising of a future good, causes pleasure; whereas, inasmuch as it implies absence of that good, it causes affliction.
Reply Obj. 3: Love and concupiscence also cause pleasure. For everything that is loved becomes pleasing to the lover, since love is a kind of union or connaturalness of lover and beloved. In like manner every object of desire is pleasing to the one that desires, since desire is chiefly a craving for pleasure. However hope, as implying a certainty of the real presence of the pleasing good, that is not implied either by love or by concupiscence, is reckoned in preference to them as causing pleasure; and also in preference to memory, which is of that which has already passed away. ________________________
FOURTH ARTICLE [I-II, Q. 32, Art. 4]
Whether sadness causes pleasure?
Objection 1: It would seem that sadness does not cause pleasure. For nothing causes its own contrary. But sadness is contrary to pleasure. Therefore it does not cause it.
Obj. 2: Further, contraries have contrary effects. But pleasures, when called to mind, cause pleasure. Therefore sad things, when remembered, cause sorrow and not pleasure.
Obj. 3: Further, as sadness is to pleasure, so is hatred to love. But hatred does not cause love, but rather the other way about, as stated above (Q. 29, A. 2). Therefore sadness does not cause pleasure.
On the contrary, It is written (Ps. 41:4): "My tears have been my bread day and night": where bread denotes the refreshment of pleasure. Therefore tears, which arise from sadness, can give pleasure.
I answer that, Sadness may be considered in two ways: as existing actually, and as existing in the memory: and in both ways sadness can cause pleasure. Because sadness, as actually existing, causes pleasure, inasmuch as it brings to mind that which is loved, the absence of which causes sadness; and yet the mere thought of it gives pleasure. The recollection of sadness becomes a cause of pleasure, on account of the deliverance which ensued: because absence of evil is looked upon as something good; wherefore so far as a man thinks that he has been delivered from that which caused him sorrow and pain, so much reason has he to rejoice. Hence Augustine says in De Civ. Dei xxii, 31 [*Gregory, Moral. iv.] that "oftentimes in joy we call to mind sad things . . . and in the season of health we recall past pains without feeling pain . . . and in proportion are the more filled with joy and gladness": and again (Confess. viii, 3) he says that "the more peril there was in the battle, so much the more joy will there be in the triumph."