_Quest._ X. Is it lawful by speech to deceive another, yea, and to intend it, supposing it be by truth? _Answ._ It is not a sin in all cases, to contribute towards another man's error or mistake.[499] For, 1. There are many cases in which it is no sin in him to mistake, nor any hurt to him: therefore to contribute to that which is neither sin nor hurt, is of itself no sin: yea, there are some cases in which an error (though not as such) may be a duty; as, to think charitably and well of a hypocrite, as long as he seemeth to be sincere. Here if by charitable reports I contribute to his mistake, it seemeth to be but my duty. For as he is bound to believe, so I am bound to report the best while it is probable. 2. There are many cases in which a man's ignorance or mistake may be his very great benefit; his life or estate may lie upon it; and I may know that if he understood such or such a thing, he would make use of it to his ruin. 3. There are many cases in which a man's innocent error is necessary to the safety of others, or of the commonwealth. 4. It is lawful in such cases to deceive such men by actions; as an enemy by military stratagems, or a traitor by signs which he will mistake. And words of truth which we foreknow he will mistake, not by our fault, but by his own, do seem to be less questionable than actions which have a proper tendency to deceive. 5. God himself hath written and spoken those words which he foreknew that wicked men would mistake and deceive themselves by; and he hath done those works, and giveth those mercies, which he knoweth they will turn to a snare against themselves. And his dominion or prerogative cannot here be pleaded to excuse it, if it were unholy. And in this sense (as to permitting and occasioning) it is said, Ezek. xiv. 9, "And if the prophet be deceived, I the Lord have deceived that prophet." Yet must we not think with Plato, that it is lawful to lie to an enemy to deceive him. For, 1. All deceit that is against charity or justice is sinful. 2. And all deceit that is performed by a lie. As Augustine saith, There are some lies which are spoken for another's safety or commodity, not in malice, but in benignity, as the midwives to Pharaoh.--These lies are not commended in themselves, but in the deceit (or charity) of them. They that thus lie will deserve (that is, be in the way) to be at last delivered from all lying. There is also a lying in jest, which deceiveth not; because he that is spoken to, knoweth it to be spoken in jest. And these two sorts are not faultless; but the fault is not great. A perfect man must not lie to save his life.--But it is lawful to silence the truth, though not speak falsely. In Psal. and in Enchirid. he saith, _Mihi non absurdum_, &c. It seemeth not absurd to me that every lie is a sin; but it is a great matter or difference, with what mind and in what matters a man lieth. Some think a physician may lie to entice his patient to take a medicine to save his life: he may lawfully deceive him by hiding a medicine, and by true speeches and dark, which he thinketh will be misunderstood; but not by falsehood.
_Quest._ XI. Wherein lieth the proper vice of lying? Is it in deceiving? or in speaking falsely? or in speaking contrary to the thoughts? _Answ._ It is the aggravation of a lie, that it be an injurious deceit. But the malignity of the sin doth not consist in the mere deceit of another man's intellect: for, as is said, it may be a great benefit to many men to be deceived: a patient's life may be saved by it, when his physician findeth it necessary to his taking a medicine, which without deceit he will not take. And so children and weak-headed people must be used. Now such a charitable deceit, as such, can be no sin. Therefore the common nature of a lie consisteth not, only, in the purpose of deceiving, but in the speaking falsely, contrary to the mind: else it would follow, either that all deceit is sin, or that all lying or false speaking is lawful, where the deceit of another is charitable or lawful: which are neither of them to be granted. Yet it is not every untruth that is a lie. Some schoolmen distinguish between _mentiri_ (as being _contra mentem ire_) and _mendacium dicere_; as if to tell a lie were not always to lie, because not contrary to the mind. But then by _mendacium_ they mean no more than _falsum_.
[Sidenote: What a lie is.]
[Sidenote: How sin is voluntary.]