Is Swearing a Sin in Christianity?

Swearing is a sin in the forms Scripture names. The Bible forbids misusing God’s name (Exodus 20:7), cursing people (James 3:9–10) and “obscene talk” (Colossians 3:8), though it never gives a list of banned words. Swearing an oath is a separate question: Jesus said, “Do not take an oath at all” (Matthew 5:34), yet most churches allow oaths in court.

James sees the whole problem in a single mouth: “With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God” (James 3:9). The tongue that prays in the morning can curse a neighbour by noon. So Scripture keeps asking what our speech is for, and Paul gives the answer in one line: words “good for building up,” so “that it may give grace to those who hear” (Ephesians 4:29).

The English word covers several kinds of speech, and Scripture treats each differently. In the Bible, to swear usually means to take an oath, calling on God, or something sacred, as a witness that we are telling the truth or will keep a promise. Cursing is something else again, the calling down of harm on someone. Profanity, or cussing, is crude or obscene language, blasphemy is speaking of God with contempt, and taking the Lord’s name in vain is using his name emptily or falsely.

Kind of speech	What it is	Key passages
Oaths	A solemn promise or statement calling on God as witness	Leviticus 19:12; Matthew 5:33–37; James 5:12
Cursing	Wishing or calling down harm on someone	Romans 12:14; James 3:9–10
Profanity or crude talk	Obscene, filthy or coarse language	Ephesians 4:29; 5:4; Colossians 3:8
Taking God’s name in vain	Using God’s name emptily, falsely or with contempt	Exodus 20:7; Leviticus 19:12
Blasphemy	Speaking against God or holy things	Leviticus 24:16; Mark 3:28–29

Often several of these come together, as they did when Peter denied Jesus in the high priest’s courtyard: “he began to invoke a curse on himself and to swear, ‘I do not know the man’” (Matthew 26:74). The King James Version renders it, “Then began he to curse and to swear.” Peter was not using coarse words; he was calling a curse down on himself and taking an oath to back up a lie.

The New Testament forbids crude and filthy talk in several places. “Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear” (Ephesians 4:29). The Greek word for corrupting, sapros, means rotten or decayed; Matthew 7:17 uses it for the “diseased tree” that “bears bad fruit.” In the next chapter Paul writes, “Let there be no filthiness nor foolish talk nor crude joking, which are out of place, but instead let there be thanksgiving” (Ephesians 5:4), and Colossians says the same: “But now you must put them all away: anger, wrath, malice, slander, and obscene talk from your mouth” (Colossians 3:8). The word translated “obscene talk” is aischrologia, shameful or filthy speech; the King James Version has “filthy communication.”

None of these passages names particular words, and the words that count as crude differ between languages and generations. Scripture looks instead at what our speech does and where it comes from. Jesus taught that “out of the abundance of the heart the mouth speaks” and that “on the day of judgment people will give account for every careless word they speak” (Matthew 12:34–36). He said that what defiles a person is what “comes out of the mouth” and “proceeds from the heart” (Matthew 15:18).

Philippians 3:8 is sometimes cited as proof that Paul himself used a swear word. Paul says he counts his former advantages as skybala, which the King James Version translates “dung,” the ESV “rubbish” and the NIV “garbage,” and some have suggested a stronger four-letter translation. Gary Manning Jr., a New Testament scholar at Biola University, searched the surviving Greek literature and found that “nowhere in all of ancient Greek literature is there a clear example of σκύβαλα functioning as a swear word or even as a rude word”; doctors, historians and philosophers used it for all kinds of waste.

The third commandment (the second in Catholic and Lutheran numbering) says: “You shall not take the name of the LORD your God in vain, for the LORD will not hold him guiltless who takes his name in vain” (Exodus 20:7). Leviticus applies it to oaths: “You shall not swear by my name falsely, and so profane the name of your God: I am the LORD” (Leviticus 19:12).

The Hebrew phrase translated “in vain,” lashav’, means for emptiness or for nothing. Catholics, Lutherans and Reformed Christians all read the commandment as forbidding every careless or contemptuous use of God’s name. The Catechism of the Catholic Church says it “forbids the abuse of God’s name, i.e., every improper use of the names of God, Jesus Christ, but also of the Virgin Mary and all the saints” (2146), and calls blasphemy “in itself a grave sin” (2148). The Westminster Larger Catechism lists among the sins it forbids any “profane” mention of God’s name and “all sinful cursings” (Q. 113). Luther’s Small Catechism also says what the name is for: “We should fear and love God that we may not curse, swear, use witchcraft, lie, or deceive by His name, but call upon it in every trouble, pray, praise, and give thanks.”

Some scholars read the commandment more widely. The verb translated “take,” nasa’, usually means to carry or bear. Carmen Joy Imes, in Bearing God’s Name: Why Sinai Still Matters (2019), argues that the commandment is about how Israel carried God’s name as his people, the way the high priest bore the names of the tribes on his garments, and not only about speech; she still holds that God’s name should be spoken with reverence.

The law of Moses allowed oaths and required people to keep them: “You shall be careful to do what has passed your lips” (Deuteronomy 23:23). Jesus went further in the Sermon on the Mount: “But I say to you, Do not take an oath at all, either by heaven, for it is the throne of God, or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. And do not take an oath by your head, for you cannot make one hair white or black. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil” (Matthew 5:34–37). James repeats the command: “do not swear, either by heaven or by earth or by any other oath, but let your ‘yes’ be yes and your ‘no’ be no” (James 5:12).

Some teachers of Jesus’ day graded oaths by what they were sworn on. Jesus quoted their rule back to them: “If anyone swears by the temple, it is nothing, but if anyone swears by the gold of the temple, he is bound by his oath.” He answered that “whoever swears by heaven swears by the throne of God and by him who sits upon it” (Matthew 23:16–22). In the Sermon on the Mount he set aside the whole system and asked for a plain word that can be trusted.

Christians have read these words of Jesus in two ways. The Anabaptists of the Reformation took them as a ban on every oath: the Schleitheim Confession of 1527 says Christ forbids his followers all swearing, true or false. Mennonites today commit themselves to a simple yes or no and affirm rather than swear in court, and Quakers refuse oaths for a similar reason; Britain Yearly Meeting’s Advices and Queries says, “Taking oaths implies a double standard of truth.”

Most other churches read Jesus as forbidding careless and evasive oaths, not every solemn one. Augustine pointed out that Paul himself swore in his letters: “For God is my witness” (Romans 1:9), and “In what I am writing to you, before God, I do not lie!” (Galatians 1:20). He concluded that an oath belongs “not among things that are good, but among things that are necessary,” because it answers the weakness of people who will not otherwise believe (Our Lord’s Sermon on the Mount 1.17.51). When the high priest put Jesus under oath, “I adjure you by the living God, tell us if you are the Christ,” Jesus answered him (Matthew 26:63–64). The Catechism of the Catholic Church says the Church has understood Jesus’ words “as not excluding oaths made for grave and right reasons (for example, in court)” (2154), but that God’s name must not be used “for trivial matters” (2155). The Westminster Confession says that “a lawful oath, being imposed by lawful authority,” in matters of weight, “ought to be taken” (22.2), and the Church of England’s Articles of Religion say that a Christian “may swear when the Magistrate requireth” (Article 39).

For most churches, then, swearing on the Bible in court is a lawful oath, while swearing “to God” to back up an everyday remark is the kind of oath Jesus and James forbade. Christians who will not swear can affirm instead. In United States federal courts, a witness “must give an oath or affirmation to testify truthfully” (Federal Rule of Evidence 603), and the Constitution lets the President “swear (or affirm).”

It is, because the New Testament tells Christians to bless even their enemies: “Bless those who persecute you; bless and do not curse them” (Romans 12:14; see also Luke 6:28 and 1 Peter 3:9). James points out the contradiction in a mouth that does both: “With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God. From the same mouth come blessing and cursing. My brothers, these things ought not to be so” (James 3:9–10).

Thomas Aquinas, who used “cursing” for wishing evil on someone, taught that it “is, of its very nature, contrary to charity” and so is “a mortal sin, according to its genus,” but that a particular curse may be venial “through the slightness of the evil invoked” or when spoken “in jest, or without deliberation” (Summa Theologiae II-II, q. 76, a. 3).

Scripture singles out blasphemy: the law of Moses made it a capital crime (Leviticus 24:16), and Jesus said that “whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin” (Mark 3:29). Catholic teaching distinguishes mortal from venial sins, and treats blasphemy as grave in itself (Catechism 2148) while allowing, as Aquinas did, that a curse spoken lightly may be venial. Reformed churches do not divide sins that way. The Westminster Confession holds that “there is no sin so small, but it deserves damnation” (15.4), yet the Westminster Larger Catechism adds that “all transgressions of the law are not equally heinous; but some sins in themselves, and by reason of several aggravations, are more heinous in the sight of God than others” (Q. 150).

Scripture addresses careless words as well as deliberate ones. Jesus said that people “will give account for every careless word they speak” (Matthew 12:36); the Greek word, argos, means idle or useless, and the King James Version has “every idle word.” Paul links angry speech with anger itself: “Let all bitterness and wrath and anger and clamor and slander be put away from you, along with all malice” (Ephesians 4:31). James advises, “let every person be quick to hear, slow to speak, slow to anger; for the anger of man does not produce the righteousness of God” (James 1:19–20).

The early church knew swearing as a habit, and John Chrysostom preached a series of sermons against the habit of swearing oaths. In his tenth homily on Acts he quoted Sirach 23:9, “Accustom not thy mouth to swearing,” and observed that “the mouth, without concurrence of the mind, articulates the word, from mere habit,” as people crossed themselves by habit when they entered the public baths. Augustine admitted in his sermons that he too had once sworn oaths every day and had fought the habit until he broke it (Sermons 180 and 307).

A habit like that can be broken, as Augustine found, and Paul tells us what to put in its place. In the same breath as he forbade crude joking, he said, “instead let there be thanksgiving” (Ephesians 5:4).

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• Bible verses about cussing
• Bible verses about controlling your tongue
• What to do if you have blasphemed the Holy Spirit