If all that the speaker says is true, you cannot accuse him of lying. To be silent is not to lie. We may say that such a man is unjust, if he ought to speak yet refuses to do so. We may say that he is disobedient, if he is commanded by lawful authority to tell the rest, and will not. But he is not a liar, for he has not said what is untrue. Thus Christ said to the Apostles “Go up to the festival day, but I go not up to this festival day.” Jn. VII., 8. Then, after they had gone without Him, “He Himself went, not openly, but in secret.” The full truth was, “I go not in the ordinary way you would expect, and with you; but I intend to go another way known to Myself alone and of which I do not wish to inform you now.” But Christ did not add the latter words, although He knew that the disciples would be misled. Yet we cannot accuse Christ, who was truth itself, of telling a lie. As a matter of fact it is not only lawful not to say what is true, but at times there may be a grave obligation not to do so. However, in certain circumstances it would be quite wrong to make use of mental restriction. Its use supposes always a justifying reason, whether of justice or of charity.
Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty