19 These sorts of lies having been without any hesitation condemned, next follows a sort, as it were by steps rising to something better, which is commonly attributed to well-meaning and good people, when the person who lies not only does no harm to another, but even benefits somebody. Now it is on this sort of lies that the whole dispute turns, whether that person does harm to himself, who benefits another in such sort as to act contrary to the truth. Or, if that alone may be called truth which illustrates the very minds of men with an intimate and incommutable light, at least he acts contrary to some true thing, because although the bodily senses are deceived, yet he acts contrary to a true thing who says that a thing is so or not so, whereof neither his mind nor senses nor his opinion or belief gives him any report.
Whether therefore he does not hurt himself in so profiting another, or in that compensation not hurt himself in which he profits the other, is a great question. If it be so, it should follow that he ought to profit himself by a lie which damages no man. But these things hang together, and if you concede that point, it necessarily draws in its train some very embarrassing consequences. For should it be asked, what harm it does to a person rolling in superfluous wealth, if from countless thousands of bushels of wheat he lose one bushel, which bushel may be profitable as necessary food to the person stealing it; it will follow that theft also may be committed without blame, and false witness borne without sin.
Than which, what can be mentioned more perverse? Or truly, if another had stolen the bushel, and you saw it done, and were questioned, would you tell a lie with honesty for the poor man, and if you do it for your own poverty will you be blamed? As if it were your duty to love another more than yourself. Both then are disgraceful, and must be avoided.
Source: On Lying (New Advent)