Today’s daf cites a mishnah which we will soon encounter on Yevamot 13:
Six women with whom relations are forbidden are more severe than these enumerated in the previous mishnah, because they may marry only others and can never be married to any of the brothers, and therefore their co-wives are permitted.
Unlike the opening mishnah, which lists the 15 categories of women who exempt their co-wives (and the co-wives of their co-wives) from the obligation to perform yibbum or halitzah, this mishnah enumerates six categories of women with whom one cannot fulfill these mitzvot, but they do not exempt their co-wives from the obligation.
One of the six categories included in the second mishnah is a mother. This refers to a case where a man’s father dies and his mother then marries his paternal half-brother (basically, her step-son). If the half-brother then dies childless, the woman would naturally fall to the surviving brother for yibbum. But that’s not possible because the woman is his mother.
The second mishnah comes to teach us that even as the surviving brother is prohibited from performing yibbum with his own mother, his mother does not exempt her co-wives from the obligation — he still can and should marry one of them.
As we learned yesterday, the sage Levi does not fully agree with the mishnah:
With regard to the case of his mother, at times she exempts her co-wife, and at other times she does not exempt her co-wife.
In other words, according to Levi, when a person’s mother falls to him as a potential for levirate marriage there are times when she exempts her co-wives and times when she does not. As a result, Levi includes the category of mother not only in the second list, but in the first list as well.
In exploring Levi’s position, the Gemara shares a number of cases in which this might be true, several of which have disturbing details. For example, the Gemara relates a situation where a man rapes his daughter-in-law and fathers a son with her. If the daughter-in-law’s husband — and the rapists’s son — then dies childless, then her own child would be in line for yibbum, since both he and the deceased are brothers (they have the same father). In such a case, Levi argues that not only is the woman exempt from yibbum, since she cannot marry her own son, but her co-wives would be exempt as well.
As a result of all of this, Levi thinks that “mother” should be included as a category not only in the second mishnah (because there are times when she does not exempt her co-wives, like the case first case described above), but in the first mishnah as well (because of the second case above, where she does).
On yesterday’s daf, we saw that Levi’s challenge to the mishnah led to the suggestion that he had a hole in his head. And although the Gemara does not ultimately adopt his view, today’s conversation shows that he might, in fact, have a leg to stand on.
Read all of Yevamot 10 on Sefaria.