Reply Obj. 1: To have the faith is not part of human nature, but it is part of human nature that man's mind should not thwart his inner instinct, and the outward preaching of the truth. Hence, in this way, unbelief is contrary to nature.
Reply Obj. 2: This argument takes unbelief as denoting a pure negation.
Reply Obj. 3: Unbelief, in so far as it is a sin, arises from pride, through which man is unwilling to subject his intellect to the rules of faith, and to the sound interpretation of the Fathers. Hence Gregory says (Moral. xxxi, 45) that "presumptuous innovations arise from vainglory."
It might also be replied that just as the theological virtues are not reduced to the cardinal virtues, but precede them, so too, the vices opposed to the theological virtues are not reduced to the capital vices. _______________________
SECOND ARTICLE [II-II, Q. 10, Art. 2]
Whether Unbelief Is in the Intellect As Its Subject?
Objection 1: It would seem that unbelief is not in the intellect as
its subject. For every sin is in the will, according to Augustine (De
Duabus Anim. x, xi). Now unbelief is a sin, as stated above (A. 1).
Therefore unbelief resides in the will and not in the intellect.
Obj. 2: Further, unbelief is sinful through contempt of the preaching of the faith. But contempt pertains to the will. Therefore unbelief is in the will.
Obj. 3: Further, a gloss [*Augustine, Enchiridion lx.] on 2 Cor. 11:14 "Satan . . . transformeth himself into an angel of light," says that if "a wicked angel pretend to be a good angel, and be taken for a good angel, it is not a dangerous or an unhealthy error, if he does or says what is becoming to a good angel." This seems to be because of the rectitude of the will of the man who adheres to the angel, since his intention is to adhere to a good angel. Therefore the sin of unbelief seems to consist entirely in a perverse will: and, consequently, it does not reside in the intellect.
On the contrary, Things which are contrary to one another are in the same subject. Now faith, to which unbelief is opposed, resides in the intellect. Therefore unbelief also is in the intellect.