A little white lie, a “necessary” untruth to ward off a greater evil. Is it permitted? Augustine of Hippo gives an uncompromising answer: no. In his sharp treatise Against Lying (Contra Mendacium) he addresses those who suppose that lying is permissible — for instance, to unmask heretics. He argues with great fire that every lie, without exception, is a sin, and why the truth alone can be the way to the truth. Read here the full English translation.

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To Consentius

The Heresy of the Priscillianists

A new heresy has arisen, that of the Priscillianists, dreadful and pernicious, which not only embraces the lie itself, but also defends it with divine authority. They hold that a Christian, in order to conceal his faith, may not only lie but even commit perjury. They cite the text, “He who speaks in his heart,” and contend that one ought to keep the truth in his heart while freely lying with the tongue before men, so as not to fall into the hands of persecutors.

They claim that even the apostle Paul did this. They construe his words, “in the wisdom of those who are without I speak,” as though he had deceived outsiders by lies in order to save them. This pernicious opinion, which makes a den of thieves of the believer’s heart, must be refuted with all our strength. If a heart that is double is condemned, how much more a heart that is not merely double but tripled by perjury?

A Lying Tongue Does Not Proceed from a Pure Heart

First of all, these men, who imagine they have a pure heart while they lie, must be asked why Scripture condemns a “double heart.” If it were possible to have the truth in the heart and to speak falsehood with the tongue, then the liar would not be double-hearted, but would have a simple heart that knows the truth and a lying tongue for some temporal good. But Scripture does not lie when it condemns the double heart.

Therefore the spirit of the liar is double; it consists of the thought of what he knows or believes to be true and conceals, and of the thought of what he knows to be false and utters. A Christian may not do this, not even to hide his faith. For he who denies Christ with his mouth does not truly have Him in his heart, since “out of the abundance of the heart the mouth speaks.”

The Eight Kinds of Lies

In another book, On Lying, I distinguished eight kinds of lies. The first is the lie in the teaching of religion, which must always be avoided. The second is the lie that unjustly harms another. The third is the one which helps one person at another’s expense. The fourth is the lie told from sheer delight in lying. The fifth is the lie told to please.

The sixth is the lie that harms no one and aids someone in his financial affairs. The seventh is the lie that harms no one and saves someone from death. The eighth is the lie that harms no one and rescues someone from bodily defilement. Some hold that the last three kinds are not sins. But I have argued that they are indeed sins, though less grave, because one may not betray the truth even for the temporal good of another.

All Lies Are Sins

The thesis that some lies are not sins is a great error. It is better to acknowledge that all lies are sins, and then to pray for forgiveness for the less grave lies, just as we pray for forgiveness of other venial sins. For who can claim to live without sin?

Let us, then, love the truth, not only in our heart but also with our mouth. Even the least harmful lie, told out of mercy, remains a sin. It is a sin committed out of compassion, but it is nonetheless a deviation from the truth. It is better to say, “I have sinned, forgive me,” than to claim that one has committed no sin.

Even the Least Lie Is a Sin, Though Venial

Let no one, then, tell me that a lie is sometimes good, or that it is no sin. For “the mouth that lies kills the soul.” And if the soul is killed, how can the lie be innocent? But there is a difference between killing a soul by a lie in religious doctrine and telling a lie to save someone’s life. The first is a mortal sin; the second, a venial sin.

We must not so twist Scripture as to claim that some lies are not sins. Rather, we must acknowledge that even the most “useful” and “merciful” lie is a sin, and apply ourselves to lying as little as possible, and to asking forgiveness when we do.

The Apostles Did Not Lie

Those who claim that lying is permitted dare even to take the apostles as their example. They allege that the apostle Paul lied when he said, “To the Jews I became as a Jew.” But this must not be taken as a lie, but as charity. He did not pretend to be a Jew by deceit, but rather, in love, lived in sympathy with their weakness.

His action was not a simulatio (pretense) but a compassio (compassion). He did not imitate their faults, but showed understanding for their condition in order to win them for Christ. It is one thing, out of love, to enter into the suffering of one who is sick; it is quite another to lie and to say that one is sick oneself.

The Lie of Rahab the Harlot

Let us now examine the examples from Scripture which are often adduced to justify lying. Rahab the harlot lied to the men of Jericho in order to save the Israelite spies. Her deed was praised — but does this mean that her lie was praised?

No, Scripture praises her faith and her hospitality toward the servants of God. Her lie was tolerated and rewarded as a sign of her conversion, just as her former life as a harlot was forgiven. Her deed is praised, not because she lied, but because she believed. The lie was the bad means that was forgiven for the sake of the good intention.

The Deed of Judith

Judith, too, is praised — not because she lied to Holofernes, but because by her courage and faith she saved the people of God. Her words were deceitful, but her purpose was holy. Scripture praises the result of her deed, but this does not mean that the lie in itself is a virtue. As with Rahab, her deed was a prophetic foreshadowing.

The Lie of Jacob

The case of Jacob, who deceived his father in order to receive the blessing, is more complex. It is not a simple example of a dutiful lie. His mother Rebekah was the driving force, and she acted on the basis of a divine revelation. The whole event is a mystery — a prophecy of how the Gentiles (Jacob) would receive the blessing destined for the Jews (Esau).

We must not imitate this action as though it were an ordinary lie, but rather seek to understand its mystery. Jacob’s lie was part of a larger, prophetic plan and cannot be used as a general justification for lying. The blessing that he received was true, even though it was obtained by a lie, which only deepens the mystery.

The Lie of the Egyptian Midwives

The Egyptian midwives lied to Pharaoh in order to save the Hebrew children, and God rewarded them. But for what did He reward them? He rewarded them for their mercy and their fear of God, not for their lie. He gave them a temporal, earthly reward (“He gave them houses”) because their deed, though well-intentioned, was not perfect.

Their lie was an imperfect deed, springing from human weakness, but their intention was good. God rewarded the good and forgave the imperfect. This shows that God can use even imperfect deeds for His plan, but it does not turn the lie itself into a virtue.

The Denial and Correction of Peter

Peter’s denial shows that even the greatest of saints can fall. We are not to imitate his fall, but his repentance. When later, out of fear of the Jews, he acted hypocritically, he was rebuked by Paul. This proves that the apostles were not above criticism, and that their actions are not always a license for us to do the same.

Paul’s correction of Peter shows that the truth, even when it is painful, stands above human fear and hypocrisy.

Lying Is Never Permitted, Not Even to Trap Heretics

Some, like the Priscillianists, claim that it is permissible to lie in order to unmask heretics. They pretend to embrace the heresy in order to win the heretics’ trust and to inform on them. This is a dreadful error.

We may not do evil that good may come of it. If we lie in order to catch a liar, we ourselves become liars. We cannot heal the sin of another by sinning ourselves. A physician who treats a sick man does not himself become sick. So too must we combat the sin of lying with the truth, not with another lie.

God Uses Lies, but Does Not Approve Them

Scripture tells us that God sent a “lying spirit” to deceive King Ahab. Does this mean that God is the source of the lie? No. God uses the evil that already exists in the will of demons and wicked men for His just judgments, but He does not create evil.

The lying spirit lied out of his own malice; God used his lie to punish Ahab. God is the just governor of all things, but He is not the author of sin. His power and wisdom are so great that He can use even the evil He does not will for a good end.

The Truth Is the Only Way to the Truth

It is absurd to think that we can bring someone to the truth by means of a lie. If we teach a heretic that lying is permissible, how can he afterwards believe us when we wish to teach him the truth of the faith? He will always suspect that we are lying out of “duty.”

The way to the truth is the truth itself. By using a lie we destroy the foundation of faith — namely, trust in the teacher. The teaching of the truth cannot be built upon a foundation of lies.

The Lie of the Physician and the Sick Man

Is it not permitted for a physician to lie to a sick patient in order to save him? Even here we must be cautious. Though the compassion be great, the deviation from the truth remains a fact. Let us grant that in an extreme case such a lie may be venial.

But this can never be applied to the doctrine of the soul. The health of the soul is the eternal truth. You cannot heal the soul with a lie, for the lie is the disease of the soul. To tell a lie in order to “save” someone for the faith is to give him poison and call it medicine.

To Save the Soul by a Lie Is Impossible

The duty to speak the truth is absolute, especially in matters of religion. He who uses a lie in order to win a soul loses his own soul. He teaches the other to lie, and so it is not heresy but lying that becomes the new norm.

If a heretic is “converted” by a lie of ours, he will think that lying is part of the Catholic faith. He, in turn, will teach the same to others. In this way we do not spread the faith, but the sin of lying.

Final Conclusion: All Lies Are Sins

My position, then, is clear and unshakable: all lies are sins. There is no such thing as a “righteous lie.” There are, to be sure, different degrees of sin in lying. It is less grievous to lie in order to save someone’s life than to lie in religious doctrine.

But even the lightest lie is a sin. Scripture is unambiguous on this point. We must not be seduced by complex reasonings that seek to rationalize evil. Let us instead beg the help of God to love and speak the truth always, and to ask forgiveness for the times when, out of weakness, we fail.

Let us pray that God may grant us the strength to defend the truth, not with deceit, but with openness and love. May He shield us from those who use the lie as a weapon, and make us steadfast in the witness of His eternal truth. Amen.

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Explicit Scriptural References in Against Lying (RSV-CE)

Below are the biblical texts that Augustine explicitly cites in this treatise.

Old Testament

• Genesis 27:12-13
  “Perhaps my father will feel me, and I shall seem to be mocking him, and bring a curse upon myself and not a blessing.” His mother said to him, “Upon me be your curse, my son; only obey my word, and go, fetch them to me.”
• Exodus 1:17, 20
  “But the midwives feared God, and did not do as the king of Egypt commanded them, but let the male children live. (…) So God dealt well with the midwives; and the people multiplied and grew very strong.”
• Joshua 2:4-6
  “But the woman had taken the two men and hidden them; and she said, ‘True, men came to me, but I did not know where they came from; and when the gate was to be closed, at dark, the men went out; where the men went I do not know; pursue them quickly, for you will overtake them.’ But she had brought them up to the roof, and hid them with the stalks of flax which she had laid in order on the roof.”
• 1 Kings 22:22
  “And he said, ‘I will go forth, and will be a lying spirit in the mouth of all his prophets.’ And he said, ‘You are to entice him, and you shall succeed; go forth and do so.’”
• Psalm 5:6
  “Thou destroyest those who speak lies; the LORD abhors bloodthirsty and deceitful men.”
• Psalm 12:2
  “Every one utters lies to his neighbor; with flattering lips and a double heart they speak.”
• Wisdom 1:11
  “(…) and a lying mouth destroys the soul.”

New Testament

• Matthew 5:37
  “Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.”
• Matthew 10:33
  “But whoever denies me before men, I also will deny before my Father who is in heaven.”
• Matthew 12:34
  “You brood of vipers! how can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks.”
• Romans 3:8
  “And why not do evil that good may come? — as some people slanderously charge us with saying. Their condemnation is just.”
• 1 Corinthians 5:12
  “For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge?”
• 1 Corinthians 9:20, 22
  “To the Jews I became as a Jew, in order to win Jews. (…) I have become all things to all men, that I might by all means save some.”
• 2 Corinthians 12:16
  “But granting that I myself did not burden you, I was crafty, you say, and got the better of you by guile.”
• Galatians 2:11-12
  “But when Cephas came to Antioch I opposed him to his face, because he stood condemned. For before certain men came from James, he ate with the Gentiles; but when they came he drew back and separated himself, fearing the circumcision party.”
• Ephesians 4:25
  “Therefore, putting away falsehood, let every one speak the truth with his neighbor, for we are members one of another.”
• 1 John 2:4
  “He who says ‘I know him’ but disobeys his commandments is a liar, and the truth is not in him.”