Reply Obj. 1: To commit sin is unlawful on account of some inordinateness therein: wherefore those which contain a greater inordinateness are more unlawful, and consequently graver sins.
Reply Obj. 2: This argument looks upon sin as though it were a pure privation.
Reply Obj. 3: Virtues are proportionately equal in one and the same subject: yet one virtue surpasses another in excellence according to its species; and again, one man is more virtuous than another, in the same species of virtue, as stated above (Q. 66, AA. 1, 2). Moreover, even if virtues were equal, it would not follow that vices are equal, since virtues are connected, and vices or sins are not. ________________________
THIRD ARTICLE [I-II, Q. 73, Art. 3]
Whether the Gravity of Sins Varies According to Their Objects?
Objection 1: It would seem that the gravity of sins does not vary according to their objects. Because the gravity of a sin pertains to its mode or quality: whereas the object is the matter of the sin. Therefore the gravity of sins does not vary according to their various objects.
Obj. 2: Further, the gravity of a sin is the intensity of its malice. Now sin does not derive its malice from its proper object to which it turns, and which is some appetible good, but rather from that which it turns away from. Therefore the gravity of sins does not vary according to their various objects.
Obj. 3: Further, sins that have different objects are of different kinds. But things of different kinds cannot be compared with one another, as is proved in Phys. vii, text. 30, seqq. Therefore one sin is not graver than another by reason of the difference of objects.
On the contrary, Sins take their species from their objects, as was shown above (Q. 72, A. 1). But some sins are graver than others in respect of their species, as murder is graver than theft. Therefore the gravity of sins varies according to their objects.