HKB
the world worketh death." But such is sloth; for it is not sorrow "according to God," which is contrasted with sorrow of the world. Therefore it is a mortal sin.
I answer that, As stated above (I-II, Q. 88, AA. 1, 2), mortal sin is so called because it destroys the spiritual life which is the effect of charity, whereby God dwells in us. Wherefore any sin which by its very nature is contrary to charity is a mortal sin by reason of its genus. And such is sloth, because the proper effect of charity is joy in God, as stated above (Q. 28, A. 1), while sloth is sorrow about spiritual good in as much as it is a Divine good. Therefore sloth is a mortal sin in respect of its genus. But it must be observed with regard to all sins that are mortal in respect of their genus, that they are not mortal, save when they attain to their perfection. Because the consummation of sin is in the consent of reason: for we are speaking now of human sins consisting in human acts, the principle of which is the reason. Wherefore if the sin be a mere beginning of sin in the sensuality alone, without attaining to the consent of reason, it is a venial sin on account of the imperfection of the act. Thus in the genus of adultery, the concupiscence that goes no further than the sensuality is a venial sin, whereas if it reach to the consent of reason, it is a mortal sin. So too, the movement of sloth is sometimes in the sensuality alone, by reason of the opposition of the flesh to the spirit, and then it is a venial sin; whereas sometimes it reaches to the reason, which consents in the dislike, horror and detestation of the Divine good, on account of the flesh utterly prevailing over the spirit. In this case it is evident that sloth is a mortal sin.
Reply Obj. 1: Sloth is opposed to the precept about hallowing the Sabbath day. For this precept, in so far as it is a moral precept, implicitly commands the mind to rest in God: and sorrow of the mind about the Divine good is contrary thereto.
Reply Obj. 2: Sloth is not an aversion of the mind from any spiritual good, but from the Divine good, to which the mind is obliged to adhere. Wherefore if a man is sorry because someone forces him to do acts of virtue that he is not bound to do, this is not a sin of sloth; but when he is sorry to have to do something for God's sake.
Reply Obj. 3: Imperfect movements of sloth are to be found in holy men, but they do not reach to the consent of reason.
FOURTH ARTICLE [II-II, Q. 35, Art. 4]
Whether Sloth Should Be Accounted a Capital Vice?
Objection 1: It would seem that sloth ought not to be accounted a capital vice. For a capital vice is one that moves a man to sinful acts, as stated above (Q. 34, A. 5). Now sloth does not move one to action, but on the contrary withdraws one from it. Therefore it should not be accounted a capital sin.
Obj. 2: Further, a capital sin is one to which daughters are assigned. Now Gregory (Moral. xxxi, 45) assigns six daughters to sloth, viz. "malice, spite, faint-heartedness, despair, sluggishness in regard to the commandments, wandering of the mind after unlawful things." Now these do not seem in reality to arise from sloth. For "spite" is, seemingly the same as hatred, which arises from envy, as stated above (Q. 34, A. 6); "malice" is a genus which contains all vices, and, in like manner, a "wandering" of the mind after unlawful things is to be found in every vice; "sluggishness" about the commandments seems to be the same as sloth, while "faint-heartedness" and "despair" may arise from any sin. Therefore sloth is not rightly accounted a capital sin.