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 an invincibly erroneous conscience concerning the malice of merely internal sins committed in thought only; but we should except efficacious desires to do what is known to be wrong. A person can scarcely know that the external action is morally wrong and be ignorant of the malice of an effective desire to commit such an action.

Again, the first principles of morality, which are certain general axioms of conduct, such as, Do to others as you would be done by, can scarcely fail to be known by anyone who has the use of reason. Even the secondary principles of the moral law, or the precepts of the Decalogue, are usually known by those who have attained the use of reason among civilized men; if in any case there is ignorance of them, it is vincible ignorance, and so more or less culpable. Theologians readily admit the possibility of an invincibly erroneous conscience concerning the application of the general principles of morality to concrete cases. The theological disputes which they chronicle are proof of the fact.