36 But for that we are men and among men do live, and I confess that I am not yet in the number of them whom compensative sins embarrass not, it oft befalls me in human affairs to be overcome by human feeling, nor am I able to resist when it is said to me, “Lo, here is a sick man in peril of his life with a grievous disease, whose strength will no more be able to bear it, if the death of his only and most dear son be announced to him; he asks of you whether his son lives, and you know that he is departed this life; what will you reply, when, whatever you shall say beside one of these three; either, He is dead; or, He lives; or, I know not; he believes no other than that he is dead; which thing he perceives you to be afraid to tell, and unwilling to tell a lie?”
It comes to the same thing, if you altogether hold your peace. But of those three, two are false, He lives, and, I know not; and they cannot be said by you but by telling a lie. Whereas if you shall say that one thing which is true, that is, that he is dead, and the man be so perturbed that death follow, people will cry out that you have killed him. And who can bear men casting up to him what a mischief it is to shun a lie that might save life, and to choose truth which murders a man?
I am moved by these objections exceedingly, but it were marvelous whether also wisely. For, when I shall set before the eyes of my heart (such as they be) the intellectual beauty of Him out of Whose mouth nothing false proceeds, albeit where truth in her radiance does more and more brighten upon me, there my weak and throbbing sense is beaten back: yet I am with love of that surpassing comeliness so set on fire, that I despise all human regards which would thence recall me. But it is much that this affection persevere to that degree, that in temptation it lack not its effect.
Nor does it move me while contemplating that luminous Good in which is no darkness of a lie, that, when we refuse to lie, and men through hearing of a truth do die, truth is called a murderer. For if a lewd woman crave of you the gratification of her lust, and, when you consent not, she perturbed with the fierceness of her love should die, will chastity also be a murderer? Or, truly, because we read, “We are a sweet savor of Christ in every place, both in them which are saved and in them which perish;” to the one, indeed, a savor of life unto life, to others a savor of death unto death; shall we pronounce even the savor of Christ to be a murderer?
But, for that we, being men, are in questions and contradictions of this sort for the most part overcome or wearied out by our feeling as men, for that very reason has the Apostle also presently subjoined, “And who is sufficient for these things?”
Source: To Consentius: Against Lying (New Advent)