Not all oaths are effective. We’ve already learned that one can’t effectively swear an oath not to perform a mitzvah. What this means, practically, is one who took an oath not to perform a mitzvah and then did the mitzvah anyway is exempt from the consequences of breaking an oath. Likewise, one who took an oath to perform a mitzvah and failed to do so is exempt.
In a beraita on today’s daf, the rabbis consider other “oaths” that might fail to take effect. For example: Can a person take an oath to inflict self harm?
One might have thought that when a person takes an oath to harm himself and he does not harm himself, he would be exempt from liability. However, the verse (about oaths) states: “… to do evil, or to do good.” (Leviticus 5:4) Just as doing good is referring to an oath about an optional action, so too, doing evil is referring to an oath about an optional action.
While the rabbis certainly don’t encourage self-harm, it is not forbidden. Because self-harm is an optional behavior, a person can effectively take an oath to hurt themselves. And, having made such an oath, become liable if they do not carry through with it.
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This is uncomfortable to contemplate — not just for us, but also the rabbis. The Tosafot point out that this beraita also appears in Tractate Bava Kamma as part of a dispute about whether self-harm is permitted at all. There, this very beraita is deployed as evidence that self-harm is permitted, though the whole discussion belies the rabbis’ discomfort with self-harm overall.
What about an oath to harm others? Will that take effect? The beraita continues:
One might have thought that when one takes an oath to harm others and does not harm them, he would be liable. Therefore the verse states: “… to do evil, or to do good.” Just as doing good is referring to an oath about an optional action, so too, doing evil is referring to an oath about an optional action. I will therefore exclude from liability one who takes an oath to harm others and he does not harm them, since it is not his prerogative to do so … And what is harming others? An example is when one takes an oath saying: “I will strike so-and-so and injure his brain.”
According to this tanna, while a person is allowed to self-harm, hurting others is never permissible. Therefore, any oath a person takes to harm another person does not take effect.
This is a good place to remind ourselves that the effectiveness of oaths, in all these cases, is not about whether they create desirable outcomes. Indeed, the verse the rabbis keep citing, about oaths which are sworn “to do evil, or to do good” makes this explicit. Rather, it is a question of whether the person swears an oath about a matter in which they actually have a choice.
This is equally true about oaths to do positive things. Two pages ago, we also saw the distinction between “doing good” for others that is volitional versus obligated: If, for example, one takes an oath to give money to a poor person and fails to do so, or swears an oath not to give money and does, they are exempt because the Torah obligates us to give money to the poor. Since giving tzedakah is not a choice, an oath to do it or not do it is ineffective. Rather, the “doing good” for which the beraita derives one is also liable refers to a case where, for example, one vowed to give or not give to a wealthy person; since such an act is not obligatory, the person’s oath takes effect, and they can be held liable for its violation.
Read all of Shevuot 27 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on May 28, 2025. If you are interested in receiving the newsletter, sign up here.
