Passiones quae sunt in irascibili et in concupiscibili, differunt specie, quia cum diversae potentiae habeant diversa obiecta (ut in primo dictum est), necesse est quod passiones diversarum potentiarum ad diversa obiecta referantur.
The passions of the irascible part differ in species from those of the concupiscible faculty because since different powers have different objects (as stated in I, q77, a3), the passions of different powers must of necessity be referred to different objects.
Bonum inquantum est delectabile, movet concupiscibilem. Sed si bonum habeat quandam difficultatem ad adipiscendum, ex hoc ipso habet aliquid repugnans concupiscibili. Et ideo necessarium fuit esse aliam potentiam quae in id tenderet. Et eadem ratio est de malis. Et haec potentia est irascibilis. Unde ex consequenti passiones concupiscibilis et irascibilis specie differunt.
Good, inasmuch as it is delightful, moves the concupiscible power. But if it prove difficult to obtain, from this very fact it has a certain contrariety to the concupiscible power. And hence the need of another power tending to that good. And the same formal aspect [of a requisite contrariety] applies to evil. And this power is the irascible faculty. Consequently the concupiscible passions are specifically different from the irascible passions.