(a) they cannot ever be invincibly ignorant of the most general precepts (such as “good is to be done,” “evil is to be avoided”), for since they know the difference between right and wrong, they must also perceive that which is contained in the concepts of right and wrong, viz., that the former is something desirable and which ought to be done, the latter something undesirable which must not be done; (b) one cannot, as a rule, be invincibly ignorant of those precepts that are immediately inferred as necessary conclusions from the most general precepts (such as “that which was borrowed must be returned”), for the conclusion follows so easily from the manifest principle that only in exceptional cases could one be excused for not knowing its truth; (c) one can, even as a rule, be ignorant of precepts that are inferred as necessary but very remote conclusions from the most general precepts, (such as “that which was borrowed must be returned at such a time or place, or in such a manner or condition”), for this conclusion is so far removed from its premise, and there are so many factors to be considered, that considerable knowledge and skill in reasoning are required for a correct judgment--things in which many people are lacking. 321. The Commandments of the Decalogue follow directly from the most general precepts of the Natural Law, and so to them may be applied what was said in the previous paragraph. Hence: (a) generally speaking, no person who has the use of reason can be invincibly ignorant of the Commandments. St. Paul blames the pagans as inexcusable in various sins committed against the Decalogue; (b) in special cases, a person who has the use of reason can be invincibly ignorant of one or more Commandments; for while the Commandments may be easily inferred by most persons from the common principles of right and wrong, there are sometimes involuntary impediments that hinder the right employment of reason. Thus, children and older persons whose mentality is undeveloped, although they know the difference between right and wrong, are frequently unable to draw the conclusion that follows from it (e.g., that one should not tell lies). 322. The Commandments regarding which invincible ignorance may most easily exist are: (a) those that deal with merely internal acts, for the malice of violating them is less apparent. Hence, many theologians admit that even among Christians the wickedness of sinful thoughts and desires may be inculpably unknown, at least when the wickedness of the corresponding external acts is also not known; (b) those that deal with the control of sensuality, for the impulse to inordinate acts is at times most vehement. Unde theologi sunt qui affirmant malitiam peccatorum externorum contra sextum invincibiliter ignorari posse, non solum apud infideles, sed etiam apud Christianos, ita quod ab adolescentibus facile ad tempus ignorari possit malitia mollitiei.