Reply Obj. 2: The midwives were rewarded, not for their lie, but for their fear of God, and for their good-will, which latter led them to tell a lie. Hence it is expressly stated (Ex. 2:21): "And because the midwives feared God, He built them houses." But the subsequent lie was not meritorious.
Reply Obj. 3: In Holy Writ, as Augustine observes (Lib. De Mend. v), the deeds of certain persons are related as examples of perfect virtue: and we must not believe that such persons were liars. If, however, any of their statements appear to be untruthful, we must understand such statements to have been figurative and prophetic. Hence Augustine says (Lib. De Mend. v): "We must believe that whatever is related of those who, in prophetical times, are mentioned as being worthy of credit, was done and said by them prophetically." As to Abraham "when he said that Sara was his sister, he wished to hide the truth, not to tell a lie, for she is called his sister since she was the daughter of his father," Augustine says (QQ. Super. Gen. xxvi; Contra Mend. x; Contra Faust. xxii). Wherefore Abraham himself said (Gen. 20:12): "She is truly my sister, the daughter of my father, and not the daughter of my mother," being related to him on his father's side. Jacob's assertion that he was Esau, Isaac's first-born, was spoken in a mystical sense, because, to wit, the latter's birthright was due to him by right: and he made use of this mode of speech being moved by the spirit of prophecy, in order to signify a mystery, namely, that the younger people, i.e. the Gentiles, should supplant the first-born, i.e. the Jews.
Some, however, are commended in the Scriptures, not on account of perfect virtue, but for a certain virtuous disposition, seeing that it was owing to some praiseworthy sentiment that they were moved to do certain undue things. It is thus that Judith is praised, not for lying to Holofernes, but for her desire to save the people, to which end she exposed herself to danger. And yet one might also say that her words contain truth in some mystical sense.
Reply Obj. 4: A lie is sinful not only because it injures one's neighbor, but also on account of its inordinateness, as stated above in this Article. Now it is not allowed to make use of anything inordinate in order to ward off injury or defects from another: as neither is it lawful to steal in order to give an alms, except perhaps in a case of necessity when all things are common. Therefore it is not lawful to tell a lie in order to deliver another from any danger whatever. Nevertheless it is lawful to hide the truth prudently, by keeping it back, as Augustine says (Contra Mend. x).
Reply Obj. 5: A man does not lie, so long as he has a mind to do what he promises, because he does not speak contrary to what he has in mind: but if he does not keep his promise, he seems to act without faith in changing his mind. He may, however, be excused for two reasons. First, if he has promised something evidently unlawful, because he sinned in promise, and did well to change his mind. Secondly, if circumstances have changed with regard to persons and the business in hand. For, as Seneca states (De Benef. iv), for a man to be bound to keep a promise, it is necessary for everything to remain unchanged: otherwise neither did he lie in promising—since he promised what he had in his mind, due circumstances being taken for granted—nor was he faithless in not keeping his promise, because circumstances are no longer the same. Hence the Apostle, though he did not go to Corinth, whither he had promised to go (2 Cor. 1), did not lie, because obstacles had arisen which prevented him.
Reply Obj. 6: An action may be considered in two ways. First, in itself, secondly, with regard to the agent. Accordingly a jocose lie, from the very genus of the action, is of a nature to deceive; although in the intention of the speaker it is not told to deceive, nor does it deceive by the way it is told. Nor is there any similarity in the hyperbolical or any kind of figurative expressions, with which we meet in Holy Writ: because, as Augustine says (Lib. De Mend. v), "it is not a lie to do or say a thing figuratively: because every statement must be referred to the thing stated: and when a thing is done or said figuratively, it states what those to whom it is tendered understand it to signify." _______________________
FOURTH ARTICLE [II-II, Q. 110, Art. 4]
Whether Every Lie Is a Mortal Sin?
Objection 1: It seems that every lie is a mortal sin. For it is written (Ps. 6:7): "Thou wilt destroy all that speak a lie," and (Wis. 1:11): "The mouth that belieth killeth the soul." Now mortal sin alone causes destruction and death of the soul. Therefore every lie is a mortal sin.
Obj. 2: Further, whatever is against a precept of the decalogue is a mortal sin. Now lying is against this precept of the decalogue: "Thou shalt not bear false witness." Therefore every lie is a mortal sin.