The Enchiridion by St. Augustine
Chapter 18.--It is Never Allowable to Tell a Lie; But Lies Differ Very Much in Guilt, According to the Intention and the Subject.
But here arises a very difficult and very intricate question, about which I once wrote a large book, finding it necessary to give it an answer. The question is this: whether at any time it can become the duty of a good man to tell a lie? For some go so far as to contend that there are occasions on which it is a good and pious work to commit perjury even, and to say what is false about matters that relate to the worship of God, and about the very nature of God Himself. To me, however, it seems certain that every lie is a sin, though it makes a great difference with what intention and on what subject one lies. For the sin of the man who tells a lie to help another is not so heinous as that of the man who tells a lie to injure another; and the man who by his lying puts a traveller on the wrong road, does not do so much harm as the man who by false or misleading representations distorts the whole course of a life. No one, of course, is to be condemned as a liar who says what is false, believing it to be true, because such an one does not consciously deceive, but rather is himself deceived. And, on the same principle, a man is not to be accused of lying, though he may sometimes be open to the charge of rashness, if through carelessness he takes up what is false and holds it as true; but, on the other hand, the man who says what is true, believing it to be false, is, so far as his own consciousness is concerned, a liar. For in saying what he does not believe, he says what to his own conscience is false, even though it should in fact be true; nor is the man in any sense free from lying who with his mouth speaks the truth without knowing it, but in his heart wills to tell a lie. And, therefore, not looking at the matter spoken of, but solely at the intention of the speaker, the man who unwittingly says what is false, thinking all the time that it is true, is a better man than the one who unwittingly says what is true, but in his conscience intends to deceive. For the former does not think one thing and say another; but the latter, though his statements may be true in fact, has one thought in his heart and another on his lips: and that is the very essence of lying. But when we come to consider truth and falsehood in respect to the subjects spoken of, the point on which one deceives or is deceived becomes a matter of the utmost importance. For although, as far as a man's own conscience is concerned, it is a greater evil to deceive than to be deceived, nevertheless it is a far less evil to tell a lie in regard to matters that do not relate to religion, than to be led into error in regard to matters the knowledge and belief of which are essential to the right worship of God. To illustrate this by example: suppose that one man should say of some one who is dead that he is still alive, knowing this to be untrue; and that another man should, being deceived, believe that Christ shall at the end of some time (make the time as long as you please) die; would it not be incomparably better to lie like the former, than to be deceived like the latter? and would it not be a much less evil to lead some man into the former error, than to be led by any man into the latter?