On yesterday’s daf, we encountered a mishnah that began:
One who betroths a woman and her daughter or a woman and her sister in one act of betrothal — neither of them is betrothed.
In ancient times, a Jewish man could have more than one wife, but it is biblically forbidden to marry two sisters or a mother and her daughter. The mishnah says that if a man attempts to betroth such a pair of women, the betrothal is completely ineffective.
The Gemara wants to know the source of this law. Rami bar Hamah suggests that it’s Leviticus 18:29, which rules that such a marriage is forbidden. But Rava challenges Rami bar Hama with this subtle observation:
If so, how would you explain what is written (at the end of that verse): “Whoever shall do any of these abominations (marrying two sisters or a mother and a daughter) … shall be cut off from among their people” (Leviticus 18:29)? If betrothal does not take effect with her, what renders him liable to receive excision from the World to Come?
Leviticus prescribes the punishment of karet, or excision, for the sin of marrying two sisters or a mother and her daughter. But if this verse is the source of the law that says simultaneous betrothal is ineffectual, how could it also be prescribing punishment for doing so? The verse must then be talking about sequential betrothal, not simultaneous betrothal, and so cannot be the source of our mishnah’s ruling.
In truth, there might be a much better explanation for the mishnah:
Let him (Rava) derive the halakhah in accordance with a principle of his own, as elsewhere (Kiddushin 9a) he establishes that betrothal that is not given to consummation is not betrothal at all.
Rava’s principle is this: If you may not have sex with her, you can’t betroth her. Betrothal, after all, is about designating a person as sexually exclusive to you. If you can’t have it, then it is not possible to claim it. Since both women in the mishnah would be forbidden if he betrothed them simultaneously, the attempted double betrothal fails.
The discussion might have ended here, but now the Gemara has another problem because it turns out that Abaye, Rava’s primary interlocutor in the Talmud, does not agree with Rava’s principle. According to Abaye, just because a person is sexually off-limits does not mean betrothal with them does not take effect.
The Gemara spends the rest of the daf teasing out which of these two great sages is correct. Can you or can’t you betroth someone who is sexually forbidden? A series of clever hypothetical scenarios are brought to test the two competing principles. Here’s the first:
We learned in the mishnah that if one attempts to betroth a woman and her daughter or a woman and her sister in one act of betrothal, neither of them is betrothed. But if he said he is betrothing only one of the two — the woman or her daughter, or the woman or her sister — without specifying which of them, then she is betrothed … So perhaps this is a conclusive refutation to the opinion of Rava.
Suppose there are two sisters, and a man betroths one of them but it is not known (even to him) which one. In this case, the Gemara points out, the betrothal is effective because there is no rule that says you can’t marry a woman with a sister. Nonetheless, the man is forbidden to have sex with either sister, since he runs the risk of accidentally sleeping with the wrong one — and that is a major offense. So in this cleverly contrived scenario, we have an example of a man who is legally betrothed to a woman he is not allowed to have sex with — which seems to refute the position of Rava that betrothal is not possible with someone who is sexually off-limits.
In all of this back and forth, there is no question about the content of the mishnah, whose meaning is perfectly clear: It is not possible to effectively betroth two sisters or a mother and daughter with one act of betrothal. The rabbis have no question about what the law is, but are asking a meta question about its source. This simple question unfurls a world of textual interpretation, general principles and complicated hypothetical scenarios. We are never in doubt about what the law says, and don’t need this discussion to know how to rule. But in the end, hopefully we do understand the entire legal system underpinning that ruling much better — which is the real point.