re in the contrary genera of virtue and vice, are not contrary to
one another in respect of their specific nature; and yet they have no
affinity or fittingness to one another. On the other hand, in those
things that are specified in relation to something extrinsic, it
happens that species belonging to contrary genera, are not only not
contrary to one another, but also that they have a certain mutual
affinity or fittingness. The reason of this is that where there is
one same relation to two contraries, there is contrariety; e.g. to
approach to a white thing, and to approach to a black thing, are
contraries; whereas contrary relations to contrary things, implies a
certain likeness, e.g. to recede from something white, and to
approach to something black. This is most evident in the case of
contradiction, which is the principle of opposition: because
opposition consists in affirming and denying the same thing, e.g.
"white" and "non-white"; while there is fittingness and likeness in
the affirmation of one contrary and the denial of the other, as, if
I were to say "black" and "not white."

Now sorrow and pleasure, being passions, are specified by their
objects. According to their respective genera, they are contrary to
one another: since one is a kind of _pursuit,_ the other a kind of
_avoidance,_ which "are to the appetite, what affirmation and denial
are to the intellect" (Ethic. vi, 2). Consequently sorrow and
pleasure in respect of the same object, are specifically contrary to
one another: whereas sorrow and pleasure in respect of objects that
are not contrary but disparate, are not specifically contrary to one
another, but are also disparate; for instance, sorrow at the death of
a friend, and pleasure in contemplation. If, however, those diverse
objects be contrary to one another, then pleasure and sorrow are not
only specifically contrary, but they also have a certain mutual
fittingness and affinity: for instance to rejoice in good and to
sorrow for evil.

Reply Obj. 1: Whiteness and blackness do not take their species from
their relationship to something extrinsic, as pleasure and sorrow do:
wherefore the comparison does not hold.

Reply Obj. 2: Genus is taken from matter, as is stated in _Metaph._
viii, 2; and in accidents the subject takes the place of matter. Now
it has been said above that pleasure and sorrow are generically
contrary to one another. Consequently in every sorrow the subject has
a disposition con