Is it ever permissible to take an oath? In the Sermon on the Mount, Jesus says, “Do not swear at all. . . . Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil” (Matt. 5:34,37). Likewise, St. James writes, “But above all, my brethren, do not swear, either by heaven or by earth or with any other oath, but let your yes be yes and your no be no, that you may not fall under condemnation” (James 5:12). Doesn’t this clearly point to an absolute prohibition against oathtaking?
The words of Jesus and James on oathtaking highlight the danger of a biblical literalism that ignores the broader cultural and scriptural context. On a surface level, they do seem to forbid oaths absolutely. But that would contradict other parts of Scripture, both the Old and New Testaments. Properly understood, neither Jesus nor James is targeting the sort of oaths taken in court or other solemn occasions. Instead, they’re responding to a culture of casual oathtaking, particularly in the legalistic way in which it was being practiced.
Oathtaking was of enormous consequence in the ancient world. Prior to forensic science and camera footage and fingerprinting, the criminal justice system leaned heavily on sworn witness testimony. That’s why the Eighth Commandment specifically forbids “false witness” (Exod. 20:16; Mark 10:19). That’s more specific than just forbidding lying (which is also wrong), because “false witness” literally refers to testimony given in court (CCC 2476). One of the ways that the integrity of oathtaking was undermined was its overuse: people swearing outside court and about inconsequential things. The other way was a complicated system of legalism that had arisen by Jesus’ day. We get a sense of this from one of Jesus’ many rebukes of the Pharisees, in which he says, “Woe to you, blind guides, who say, ‘If any one swears by the temple, it is nothing; but if any one swears by the gold of the temple, he is bound by his oath’” (Matt. 23:16).
The Jews tended to avoid swearing “by God” (out of a holy fear), and so they swore instead by something associated with God—the temple (or the gold of the temple), or the altar, or the sacrificial gift upon the altar, or heaven, or earth, or Jerusalem, or one’s own person (see Matt. 5:34-36, 23:18). The Pharisees had elaborate rules about which of these objects created a binding oath and which didn’t. Because of these loopholes, a person could take an oath, knowing he wouldn’t be bound to keep it. The honesty and trust that oaths existed to cement was thus undermined in favor of a system that rewarded carefully worded dishonesty.
In attacking the culture of oathtaking, Jesus exposes this whole system of man-made legalism as an elaborate fiction. No matter whom or what you’re swearing by, you’re ultimately swearing by God, since “he who swears by the temple, swears by it and by him who dwells in it; and he who swears by heaven, swears by the throne of God and by him who sits upon it” (Matt. 23:21-22). Since “you cannot make one hair white or black” (Matt. 5:36), even swearing by yourself was ultimately swearing by the God who sustains you. In other words, whether you’re swearing by God or by something in creation, you’re ultimately swearing by God. Pretending that you’re swearing only “by heaven” or “by the gold of the temple” is just an evasion.
But does this mean we should literally never take oaths, even in court? So it may appear, at first. But remember that the Eighth Commandment forbids false witness (Exod. 20:16). Taking Jesus to be forbidding any sworn testimony would actually preclude bearing true witness, as well. But there’s a second problem. We see St. Paul himself taking oaths in Scripture twice, when he finds it important to stress the truth and reliability of what he’s saying. To the Corinthians, he writes, “But I call God to witness against me—it was to spare you that I refrained from coming to Corinth” (2 Cor. 1:23). And to the Galatians: “In what I am writing to you, before God, I do not lie!” (1:20).
On a literal level, St. Paul would seem to be violating divine law here. But Paul’s oathtaking is different from that of the type that Jesus condemned, for a few reasons. First, he’s invoking God directly, rather than invoking something associated with God. This is actually what God commands: “You shall fear the Lord your God; you shall serve him, and swear by his name” (Deut. 6:13). If you’re in a situation in which oathtaking is called for, don’t swear by someone or something less than God. Second, he’s doing it judiciously—Paul isn’t just casually peppering his speech with “I swear to God!” the way some modern speakers do. And third, he’s telling the truth. (In contrast, to see what Christian oathtaking shouldn’t look like, see St. Peter’s impulsive and false oath in Matt. 26:72). These distinctions are neatly captured in the Code of Canon Law, which specifies that “an oath, that is, the invocation of the divine name in witness to the truth, cannot be taken unless in truth, in judgment, and in justice” (Can. 1199 §1; see CCC 2154).
Instead of settling for a surface-level literalism, understanding Jesus’ words about oathtaking requires knowing something about the culture in which he spoke, the abuses of oathtaking of which the Pharisees were guilty, and the proper oathtaking that Paul models. Taken as a whole, we see that Jesus and James aren’t telling us that we may never take oaths, even in court or on solemn occasions. Instead, they’re telling us not to take oaths lightly, and not to play legalistic games with them. Taking oaths seriously upholds the integrity of oathtaking—that is, if oaths are taken only sparingly, and “in truth, in judgment, and in justice,” then they’re trustworthy, whereas oaths taken flippantly might not be.