(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.
(b) Culpable ignorance is not distinct from its effect (i.e., from a sin committed on account of the ignorance), if the truth one is ignorant of has to be known only on account of some passing duty that must be performed here and now; for in such a case the knowledge is required, not for its own sake, but for the sake of the duty. Hence, ignorance of fact or of a particular law is not distinct as a sin from the sin that results from it. Examples: Titus knows that he should not take money that belongs to another; but through his own carelessness he is ignorant of the fact that the money before him belongs to another, and takes the money. Balbus knows that the precept of the Church on fasting is obligatory; but through his own negligence he is unaware that today is a fast day, and does not fast. Titus and Balbus committed one sin apiece.
(c) Culpable ignorance is distinct from its effect, if the truth one is ignorant of has to be known for its own sake; for in such a case one sins against the virtue of studiosity (see 905) by not knowing something which one should know habitually, and also against some other virtue by violating its precepts as a result of one’s sinful ignorance. Truths one is obliged to know for their own sake are the mysteries of faith, the Commandments of the Decalogue, the Precepts of the Church, and the duties of one’s own state. Examples: Sempronius through his own carelessness does not know the mystery of the Incarnation, and as a result blasphemes Christ. Titus does not know that stealing is a sin, and therefore he steals. In both cases two sins are committed, the sin of ignorance and the sin that resulted from ignorance.
908. Cases in which ignorance in matters of faith is not culpable are the following: (a) if one has used sufficient diligence to acquire knowledge, one is not responsible for one’s ignorance; (b) if one has not used sufficient diligence to acquire knowledge, one is not responsible for one’s ignorance, if the lack of diligence is not one’s fault.
909. Sufficient diligence is a broad term and has to be understood with relation to the mental ability of the person and the importance and difficulty of the truth in question. What is sufficient diligence in an illiterate person, or with regard to a matter of minor importance, would be insufficient in a learned person, or in a matter of greater importance. However, the following general rules can be given: