The Enchiridion 22
22 A Lie is Not Allowable, Even to Save Another from Injury PL 40, 243
But every lie must be called a sin, because not only when a man knows the truth, but even when, as a man may be, he is mistaken and deceived, it is his duty to say what he thinks in his heart, whether it be true, or whether he only think it to be true. But every liar says the opposite of what he thinks in his heart, with purpose to deceive. Now it is evident that speech was given to man, not that men might therewith deceive one another, but that one man might make known his thoughts to another. To use speech, then, for the purpose of deception, and not for its appointed end, is a sin. Nor are we to suppose that there is any lie that is not a sin, because it is sometimes possible, by telling a lie, to do service to another. For it is possible to do this by theft also, as when we steal from a rich man who never feels the loss, to give to a poor man who is sensibly benefited by what he gets. And the same can be said of adultery also, when, for instance, some woman appears likely to die of love unless we consent to her wishes, while if she lived she might purify herself by repentance; but yet no one will assert that on this account such an adultery is not a sin. And if we justly place so high a value upon chastity, what offense have we taken at truth, that, while no prospect of advantage to another will lead us to violate the former by adultery, we should be ready to violate the latter by lying? It cannot be denied that they have attained a very high standard of goodness who never lie except to save a man from injury; but in the case of men who have reached this standard, it is not the deceit, but their good intention, that is justly praised, and sometimes even rewarded. It is quite enough that the deception should be pardoned, without its being made an object of laudation, especially among the heirs of the new covenant, to whom it is said: “Let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.” And it is on account of this evil, which never ceases to creep in while we retain this mortal vesture, that the co-heirs of Christ themselves say, “Forgive us our debts.”
Omne mendacium esse peccatum. Porro autem omne mendacium ideo dicendum est esse peccatum, quia homo non solum quando scit ipse quod verum sit, sed etiam si quando errat et fallitur sicut homo, hoc debet loqui quod animo gerit; sive illud verum sit, sive putetur et non sit. Omnis autem qui mentitur, contra id quod animo sentit loquitur voluntate fallendi. Et utique verba propterea sunt instituta, non per quae se homines invicem fallant, sed per quae in alterius quisque notitiam cogitationes suas perferat. Verbis ergo uti ad fallaciam, non ad quod instituta sunt, peccatum est. Nec ideo ullum mendacium putandum est non esse peccatum, quia possumus aliquando alicui prodesse mentiendo. Possumus enim et furando, si pauper cui palam datur, sentit commodum, et dives cui clam tollitur, non sentit incommodum: nec ideo tale furtum quisquam dixerit non esse peccatum. Possumus et adulterando, si aliqua, nisi ad hoc ei consentiatur, appareat amando moritura, et si vixerit, poenitendo purganda: nec ideo peccatum negabitur tale adulterium. Si autem merito nobis placet castitas, quid offendit veritas, ut propter alienam utilitatem illa non violetur adulterando, et violetur ista mentiendo? Plurimum quidem ad bonum profecisse homines, qui non nisi pro salute hominis mentiuntur, non est negandum: sed in eorum tali profectu merito laudatur, vel etiam temporaliter remuneratur benevolentia, non fallacia, quae ut ignoscatur sat est, non ut etiam praedicetur, maxime in haeredibus Testamenti Novi, quibus dicitur, Sit in ore vestro, Est, est; Non, non: quod enim amplius est, a malo est . Propter quod malum, quia subrepere in hac mortalitate non desinit, etiam ipsi cohaeredes Christi dicunt, Dimitte nobis debita nostra .