What Does the Church Teach About Swearing and Cursing?

Is swearing a sin? It depends on what is meant by the word, and Scripture and the Catholic Church draw the line cleanly. To swear an oath — to call God to witness the truth — is lawful and even holy when done reverently and for a just cause. To swear in vain, that is, to take the holy name of God lightly, falsely, or in anger, is a sin against the Second Commandment, and when it rises to contempt of God it becomes blasphemy, a grave sin. And the loose, foul, coarse speech that men today also call "swearing" is forbidden too, not as blasphemy but as the corrupt talk that Scripture commands the Christian to put away. We say all this plainly, because the tongue is the hardest member to govern, and a soul is owed the truth about it.

What does the Bible say about swearing?

The foundation is the Second Commandment, given on Sinai:

Thou shalt not take the name of the Lord thy God in vain: for the Lord will not hold him guiltless that shall take the name of the Lord his God in vain. (Exodus xx. 7, Douay-Rheims)

God attaches a warning to almost no other commandment as He does to this one: He "will not hold him guiltless." The name of God is holy, and to drag it into idle speech, false oaths, or curses is to profane what is most sacred. This is the root of every sin of the tongue against God.

Our Lord then deepens the commandment in the Sermon on the Mount, warning against the careless multiplying of oaths:

But I say to you not to swear at all, neither by heaven, for it is the throne of God: nor by the earth, for it is his footstool... But let your speech be yea, yea: no, no: and that which is over and above these, is of evil. (Matthew v. 34-37, Douay-Rheims)

"Let your speech be yea, yea." Christ is not abolishing every lawful oath — He Himself answered under oath before the high priest, and St Paul calls God to witness in his letters (Romans i. 9). What Christ forbids is the habit of swearing as a verbal tic, scattering oaths to be believed, when an honest man's plain word should suffice. The Christian is to be so truthful that he needs no oath at all.

St James returns to the same point with great force:

But above all things, my brethren, swear not, neither by heaven, nor by the earth, nor by any other oath. But let your speech be: Yea, yea: No, no: that you fall not under judgment. (James v. 12, Douay-Rheims)

And the same Apostle gives the sharpest warning in all Scripture about the danger of the tongue:

The tongue is a fire, a world of iniquity... By it we bless God and the Father: and by it we curse men, who are made after the likeness of God. Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be. (James iii. 6-10, Douay-Rheims)

Oaths, vain swearing, and blasphemy: the three things

The single English word "swearing" covers three very different things, and the moral tradition keeps them carefully apart.

A lawful oath is good

An oath is the act of calling God to witness the truth of what we say. The Roman Catechism teaches that to swear "by the name of God" reverently, truthfully, and in a just cause is not only lawful but an act of honour paid to God, for it confesses that He is the searcher of hearts and the avenger of falsehood (Catechism of the Council of Trent, on the Second Commandment). Three conditions make an oath honest, drawn from the prophet:

And thou shalt swear: As the Lord liveth, in truth, and in judgment, and in justice. (Jeremias iv. 2, Douay-Rheims)

That is, an oath must be sworn in truth (the thing sworn is true), in judgment (with due reverence and necessity, not rashly), and in justice (the thing sworn is itself lawful). A courtroom oath or a solemn vow rightly taken is no sin at all.

Vain swearing is a sin against the Second Commandment

To use God's holy name carelessly — as a thoughtless exclamation, in anger, in jest, or to back a trivial claim — is to take that name "in vain." To swear falsely, calling God to witness a lie, is perjury, a grave sin that makes God the guarantor of a falsehood. The habit of peppering one's speech with the name of God or with rash oaths is, even when half-thoughtless, a real fault that wears down reverence in the soul.

Blasphemy is a grave sin

Blasphemy is speech that insults, mocks, reviles, or expresses contempt for God, His holy name, the Blessed Virgin, or the saints. It is not merely irreverent; it is directed against God Himself. St Thomas Aquinas teaches that blasphemy, because it attacks God directly, is in its kind a graver sin even than murder, which harms only a creature (Summa Theologiae II-II, q. 13). The old Law marked its gravity without ambiguity:

And he that blasphemeth the name of the Lord, dying let him die. (Leviticus xxiv. 16, Douay-Rheims)

Cursing — calling down evil or damnation on another person, especially using God's name to do it — belongs here too as a sin against charity and against God. To wish a soul to hell is the very opposite of the love Christ commands.

What about coarse, foul language?

Much of what people today call "swearing" is not an oath or blasphemy at all, but simply vulgar, obscene, or filthy talk. Scripture forbids this as well, not as a sin against God's name directly, but as the corrupt speech unworthy of a redeemed soul:

Let no evil speech proceed from your mouth: but that which is good, to the edification of faith, that it may administer grace to the hearers. (Ephesians iv. 29, Douay-Rheims)

But fornication and all uncleanness or covetousness, let it not so much as be named among you, as becometh saints: or obscenity or foolish talking or scurrility, which is to no purpose. (Ephesians v. 3-4, Douay-Rheims)

The gravity of foul language varies with its content and intent. Habitual coarse speech is usually a venial fault — a lapse of self-government and charity that coarsens the soul and scandalises others. But obscene talk that excites lust, or speech that mocks sacred things, can be a grave matter. The rule is the one our Lord gave: speech ordered to truth, charity, and the edification of those who hear, never to corruption.

How does a soul govern the tongue?

The tongue is governed not by gritted teeth alone but by grace and habit, the means the saints have always used.

• Reverence the name of God. Cultivate love for the holy name of Jesus, and irreverent speech withers at the root. The old custom of bowing the head at the Holy Name trains the soul to hold it sacred.
• Make reparation. When the name is profaned, answer it. Pray the divine praises — "Blessed be God, blessed be His holy name" — composed precisely as reparation for blasphemy.
• Confess the habit. Vain swearing and foul speech are exactly the matter for an honest examination of conscience and a good confession. If it has been long, our walk-through on how to go to confession will steady you.
• Cut the root. Sins of the tongue feed on anger, pride, and idle company. See what God says about anger, and learn the watchfulness the masters of spiritual combat teach for governing the first stirrings of speech.

The man who masters his tongue, St James says, is "a perfect man." None of us is yet perfect, but the road is open, and grace is given daily to those who ask it on their knees.

Frequently Asked Questions

Is swearing a sin in the Catholic Church?

It depends on the kind of swearing. A reverent, truthful oath sworn for a just cause is lawful and good. But taking God's holy name in vain — carelessly, falsely, in anger, or in jest — is a sin against the Second Commandment. Foul and obscene language is also forbidden as corrupt speech (Ephesians iv. 29), usually a venial fault but graver when it mocks the sacred or excites lust.

What does the Bible say about taking God's name in vain?

The Second Commandment states it directly: "Thou shalt not take the name of the Lord thy God in vain: for the Lord will not hold him guiltless that shall take the name of the Lord his God in vain" (Exodus xx. 7, Douay-Rheims). God attaches a solemn warning to this commandment because His name is holy and must be reverenced.

What is the difference between swearing an oath and cursing?

An oath calls God to witness the truth of what we say, and is lawful when sworn in truth, judgment, and justice (Jeremias iv. 2). Cursing calls down evil or damnation on another, often abusing God's name to do so; it is a sin against both God and charity. Blasphemy — speech expressing contempt for God or holy things — is the gravest of these (Summa Theologiae II-II, q. 13).

Did Jesus forbid all swearing?

No. When Christ said "swear not at all" and "let your speech be yea, yea" (Matthew v. 34-37), He forbade the careless habit of scattering oaths to be believed, not every lawful oath. He Himself answered under oath before the high priest, and St Paul calls God to witness in his letters (Romans i. 9). The Christian is called to be so truthful that no oath is needed.

Is using bad language a mortal sin?

Usually coarse or vulgar language is a venial sin — a lapse of charity and self-government. It can become grave matter when it is genuinely blasphemous (expressing contempt for God), when it is obscene speech meant to excite lust, or when it gravely scandalises others. The remedy in every case is reverence, charity in speech, and sacramental confession.

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Sources. Douay-Rheims Bible (Exodus xx. 7; Leviticus xxiv. 16; Jeremias iv. 2; Matthew v. 34-37; Romans i. 9; Ephesians iv. 29, v. 3-4; James iii. 6-10, v. 12); St Thomas Aquinas, Summa Theologiae II-II, q. 13; Catechism of the Council of Trent (the Roman Catechism), on the Second Commandment.