Whether unbelief is a sin?
Objection 1: It would seem that unbelief is not a sin. For every sin is contrary to nature, as Damascene proves (De Fide Orth. ii, 4). Now unbelief seems not to be contrary to nature; for Augustine says (De Praedest. Sanct. v) that "to be capable to having faith, just as to be capable of having charity, is natural to all men; whereas to have faith, even as to have charity, belongs to the grace of the faithful." Therefore not to have faith, which is to be an unbeliever, is not a sin.
Objection 2: Further, no one sins that which he cannot avoid, since every sin is voluntary. Now it is not in a man's power to avoid unbelief, for he cannot avoid it unless he have faith, because the Apostle says (Rom. 10:14): "How shall they believe in Him, of Whom they have not heard? And how shall they hear without a preacher?" Therefore unbelief does not seem to be a sin.
Objection 3: Further, as stated above (FS, Q 84, A 4), there are seven capital sins, to which all sins are reduced. But unbelief does not seem to be comprised under any of them. Therefore unbelief is not a sin.
On the contrary, Vice is opposed to virtue. Now faith is a virtue, and unbelief is opposed to it. Therefore unbelief is a sin.
I answer that, Unbelief may be taken in two ways: first, by way of pure negation, so that a man be called an unbeliever, merely because he has not the faith. Secondly, unbelief may be taken by way of opposition to the faith; in which sense a man refuses to hear the faith, or despises it, according to Is. 53:1: "Who hath believed our report?" It is this that completes the notion of unbelief, and it is in this sense that unbelief is a sin.
If, however, we take it by way of pure negation, as we find it in those who have heard nothing about the faith, it bears the character, not of sin, but of punishment, because such like ignorance of Divine things is a result of the sin of our first parent. If such like unbelievers are damned, it is on account of other sins, which cannot be taken away without faith, but not on account of their sin of unbelief. Hence Our Lord said (Jn. 15:22) "If I had not come, and spoken to them, they would not have sin"; which Augustine expounds (Tract. lxxxix in Joan.) as "referring to the sin whereby they believed not in Christ."
Reply to Objection 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 to Objection 2: This argument takes unbelief as denoting a pure negation.
Reply to Objection 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.
II–II · Q. 10, Art. 2: Whether unbelief is in the intellect as its subject?
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.
Objection 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.
Objection 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.
I answer that, As stated above (FS, Q 74, AA 1,2), sin is said to be in the power which is the principle of the sinful act. Now a sinful act may have two principles: one is its first and universal principle, which commands all acts of sin; and this is the will, because every sin is voluntary. The other principle of the sinful act is the proper and proximate principle which elicits the sinful act: thus the concupiscible is the principle of gluttony and lust, wherefore these sins are said to be in the concupiscible. Now dissent, which is the act proper to unbelief, is an act of the intellect, moved, however, by the will, just as assent is.
Therefore unbelief, like faith, is in the intellect as its proximate subject. But it is in the will as its first moving principle, in which way every sin is said to be in the will.
Hence the Reply to the First Objection is clear.
Reply to Objection 2: The will's contempt causes the intellect's dissent, which completes the notion of unbelief. Hence the cause of unbelief is in the will, while unbelief itself is in the intellect.
Reply to Objection 3: He that believes a wicked angel to be a good one, does not dissent from a matter of faith, because "his bodily senses are deceived, while his mind does not depart from a true and right judgment" as the gloss observes [*Augustine, Enchiridion lx]. But, according to the same authority, to adhere to Satan when he begins to invite one to his abode, i.e. wickedness and error, is not without sin.