The duty always to tell the truth does not imply the obligation always to tell all you know; and falsehood does not always follow as a result of not revealing your mind to the first inquisitive person that chooses to put embarrassing questions. Alongside, but not contrary to, the duty of veracity is the right every man has to personal and professional secrets. For a man’s mind is not public property; there may arise at times circumstances in which he not only may, but is in duty bound to withhold information that concerns himself intimately or touches a third person; and there must be a means to protect the sacredness of such secrets against undue curiosity and inquisitiveness, without recourse to the unlawful method of lying. Silence is not an effective resource, for it not infrequently gives consent one or the other way; the question may be put in such a manner that affirmation or negation will betray the truth. To what then shall one have recourse?
Let us remark in the first place that God has endowed human intelligence with a native wit, sharpness and cunning that has its legitimate uses, the exercise of this faculty is evil only when its methods and ends are evil. Used along the lines of moral rectitude strategy and tact for profiting by circumstances are perfectly in order, especially when one acts in the defense of his natural rights. And if this talent is employed without injustice to the neighbor or violence to the law of God, it is no more immoral than the plain telling of truth; in fact it is sometimes better than telling the truth.
But it must be understood that such practices must be justified by the circumstances. They suppose in him who resorts thereto a right to withhold information that overrides the right of his interrogator. If the right of the latter to know is superior, then the hiding of truth would constitute an injustice, which is sinful, and this is considered tantamount to lying. And if the means to which we resort is not lying, as we have defined it, that is, does not show a contradiction between what we say and what we mean, then there can be no fear of evil on any side.
Now, suppose that instead of using a term whose signification is contrary to what my mind conceives, which would be falsehood, I employ a word that has a natural double meaning, one of which is conform to my mind, the other at variance. In the first place, I do not speak against my mind; I say what I think; the word I use means what I mean. But the other fellow! that is another matter. He may take his choice of the two meanings. If he guesses aright, my artifice has failed; if he is deceived, that is his loss. I do him no injustice, for he had no right to question me. If my answer embarrasses him, that is just what I intended, and I am guilty of no evil for that; if it deceives him, that I did not intend but willingly suffer; I am not obliged to enter into explanations when I am not even bound to answer him. Of the deception, he alone is the cause; I am the occasion, if you will, but the circumstances of his inquisitiveness made that occasion necessary, and I am not responsible.
This artifice is called equivocation or amphibology; it consists in the use of words that have a natural double meaning; it supposes in him who resorts to it the right to conceal the truth, a right superior to that of the tormentor who questions him. When these conditions are fulfilled, recourse to this method is perfectly legitimate, but the conditions must be fulfilled. This is not a weapon for convenience, but for necessity. It is easy to deceive oneself when it is painful to tell the truth. Therefore it should be used sparingly: it is not for every-day use, only emergencies of a serious nature can justify its employ.
Another artifice, still more delicate and dangerous, but just as legitimate when certain conditions are fulfilled, is what is known as mental restriction. This too consists in the employ of words of double meaning; but whereas in the former case, both meanings are naturally contained in the word, here the term employed has but one natural signification, the other being furnished by circumstances. Its legitimate use supposes that he to whom the term is directed should either in fact know the circumstances of the case that have this peculiar significance, or that he could and should know them. If the information drawn from the answer received is insufficient, so much the better; if he is misinformed, the fault is his own, since neither genuine falsehood nor evident injustice can be attributed to the other.
An example will illustrate this better than anything else. Take a physician or lawyer, the custodian of a professional secret, or a priest with knowledge safeguarded by the seal of the confessional. These men either may not or should not reveal to others unconcerned in the matter the knowledge they possess. There is no one but should be aware of this, but should know that when they are questioned, they will answer as laymen, and not as professionals. They will answer according to outside information, yes or no, whether on not such conclusion agree with the facts they obtained under promise of secrecy. They simply put out of their mind as unserviceable all professional knowledge, and respond as a man to a man. Their standing as professional men puts every questioner on his guard and admonishes him that no private information need be expected, that he must take the answer given as the conclusion of outside evidence, then if he is deceived he has no one to blame but himself, since he was warned and took no heed of the warning.
Again we repeat, the margin between mental restriction and falsehood is a safe, but narrow one, the least bungling may merge one into the other. It requires tact and judgment to know when it is permissible to have recourse to this artifice and how to practice it safely. It is not a thing to be trifled with. In only rare circumstances can it be employed, and only few persons have the right to employ it.