905. Ignorance (as explained in 28 and 249) is a cause of sin--of material sin, if the ignorance is antecedent, of formal sin, if the ignorance is consequent. But ignorance is also a sin itself, in the sense now to be explained. (a) Ignorance may be considered in itself (i.e., precisely as it is the absence of knowledge), and in this sense it is not called a sin, since under this aspect it is not opposed to moral virtue, but to knowledge, the perfection of the intellect. (b) Ignorance may be considered in relation to the will (i.e., precisely as it is a voluntary defect), and in this sense it is a sin, since under this aspect it is opposed to the moral virtue of studiosity (i.e., the part of temperance which moderates the desire of learning and keeps the golden mean between curiosity and negligence). This sin of ignorance pertains to neglect, and is twofold; it is called affected ignorance, if the will is strongly desirous of the lack of due knowledge, and is called careless ignorance, if the will is remiss in desiring due knowledge. Affected ignorance is a sin of commission, careless ignorance a sin of omission. (c) Ignorance may be considered in relation to obligatory acts (i.e., precisely as it makes one voluntarily incapable of fulfilling one’s duties), and in this sense it partakes of various kinds of sinfulness, inasmuch as he who is voluntarily ignorant of his duty is responsible for the mistakes he will make. Thus, he who is sinfully ignorant in matters of faith, will fail against the precepts of that virtue; he who does not know what his state of life as judge, lawyer, physician, etc., requires, will fail against justice; he who does not know what charity demands of him, will sin against charity. 906. The malice of the sin of ignorance in matters of faith is as follows: (a) Vincible ignorance of the truths one is obliged to know, whether the obligation be of means or of precept (see 360, 786 sqq.), is a grave sin, for faith in these truths is commanded under pain of losing salvation (Mark, xvi. 15, 16). (b) The sin committed is but one sin, regardless of length of time, and is incurred at the time one omits due diligence in acquiring knowledge, as is the case with other sins of omission. Hence, he who remains in culpable ignorance of Christian doctrine for a year commits one sin, but the length of time is an aggravating circumstance. 907. Culpable ignorance regarding truths of faith, as a distinct sin, is as follows: (a) It is not distinct from its cause (i.e., negligence), for ignorance is not a sin at all, except in so far as it proceeds from negligence. Hence, one would not be obliged to accuse oneself of the sins of omission in regard to instruction in Christian doctrine and of ignorance in Christian doctrine, for these are but one sin.