816. Direct sins of unbelief are those opposed to the elements that belong to the nature of faith and that are contained in its definition (see 751, 798). (a) Opposed to the act of assent are sins of non-assent or dissent (see 817-839); (b) opposed to the certitude and firmness of assent are sins of doubt (840-846); (c) opposed to the right object of faith are sins of credulity (847); (d) opposed to the motive of faith is rationalism (847). 817. Sins of non-assent are those by which one omits to make an act of faith when one should. This kind of sin will be treated when we come to the commandments of faith as to its internal and external acts (see 925 sqq.) 818. Sins of dissent are sins of commission, and are of two kinds: (a) privative unbelief, which is the want of faith in one who has heard the faith sufficiently and should realize the obligation of embracing it, but who refuses to believe, although he makes no opposition to faith; (b) contrary unbelief, which is the want of faith in one who has heard the faith and its motives of credibility sufficiently to know the duty of embracing it, and who not only refuses to believe, but even accepts the errors opposed to faith. 819. What is the gravity of sins of dissent, doubt, and rationalism? (a) From their nature, these sins are always mortal, for they refuse to God the homage of the intellect and will that is due Him, deprive man of the beginning of spiritual life, and lead to eternal condemnation (Mark, xvi. 16). (b) From their circumstances, these and other sins against faith may be venial (see 180-184). Thus, if a man refuses to believe or accepts error, not having sufficient knowledge of his obligation or not fully consenting to the sin, his fault is venial subjectively or formally. 820. Are sins against faith more serious than all other kinds of sin? (a) From their nature, sins against faith are worse than sins against the moral virtues, for the former offend directly against God Himself, but not so the latter. Hatred of God, however, is a greater sin than sins of unbelief, as will be shown when we treat of sins against charity. (b) From their circumstances, sins against faith may be less serious than sins against the moral virtues. Example: A venial sin against faith is less serious than a mortal sin against justice. 821. With regard to the effect of sins against faith on good acts it should be noted: (a) an unbeliever is able to perform works that are ethically or naturally good (Rom., ii. 14), and the Church has condemned the opposite teaching of Baius (Denzinger, _Enchiridion_, n. 1025). (b) an unbeliever is not able to perform works that are supernaturally good and meritorious (see 112).