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.

❌ Objection 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.

❌ Objection 3 : Further, Augustine says (De Doctr. Christ. i, 36): "Every liar breaks his faith in lying, since forsooth he wishes the person to whom he lies to have faith in him, and yet he does not keep faith with him, when he lies to him: and whoever breaks his faith is guilty of iniquity." Now no one is said to break his faith or "to be guilty of iniquity," for a venial sin. Therefore no lie is a venial sin.

❌ Objection 4 : Further, the eternal reward is not lost save for a mortal sin. Now, for a lie the eternal reward was lost, being exchanged for a temporal meed. For Gregory says (Moral. xviii) that "we learn from the reward of the midwives what the sin of lying deserves: since the reward which they deserved for their kindness, and which they might have received in eternal life, dwindled into a temporal meed on account of the lie of which they were guilty." Therefore even an officious lie, such as was that of the midwives, which seemingly is the least of lies, is a mortal sin.

❌ Objection 5 : Further, Augustine says (Lib. De Mend. xvii) that "it is a precept of perfection, not only not to lie at all, but not even to wish to lie." Now it is a mortal sin to act against a precept. Therefore every lie of the perfect is a mortal sin: and consequently so also is a lie told by anyone else, otherwise the perfect would be worse off than others.