as one thing is in real conjunction of any
kind with another, either actually or potentially. And since real
conjunction is greater than conjunction by likeness, which is the
conjunction of knowledge; and again, since actual is greater than
potential conjunction: therefore the greatest pleasure is that which
arises from sensation which requires the presence of the sensible
object. The second place belongs to the pleasure of hope, wherein
there is pleasurable conjunction, not only in respect of
apprehension, but also in respect of the faculty or power of
obtaining the pleasurable object. The third place belongs to the
pleasure of memory, which has only the conjunction of apprehension.

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.
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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.