As we learned on yesterday’s daf, Beit Hillel believes that if a man was married to two women, one of whom was forbidden to marry his brother, in the event that he dies without children, neither she nor her rival wife (a tzarah in the language of the Mishna), will become yevamot. According to Beit Shammai, however, the tzarah is treated independently and will be subject to the rules of yibum and/or halitza as if she had been the only wife of the deceased. The Mishna comments that their disagreement notwithstanding, the families of Beit Shammai and Beit Hillel continued to marry one another.
This agreement is somewhat surprising, since the ramifications of performing yibum when it is forbidden can be severe, including the birth of offspring that may be considered to be mamzerim!
The Gemara first suggests that following the public ruling that Beit Hillel’s positions are the ones accepted by the halakha, perhaps Beit Shammai accepted Beit Hillel’s rulings and did not act on their own positions. Rabbi Yohanan rejects that suggestion, arguing – and illustrating by way of examples – that they not only followed their own rulings, but that they also ruled that way for others!
The conclusion of the Gemara is that both families relied on each other to inform them if the prospective bride or groom was from a marriage that involved a relationship that the other felt was forbidden. With that information there was no problem for them to marry one another. The Ritva explains that they relied on each other to the extent that if no alert was forthcoming from the other family, it was assumed and accepted that the suggested marriage did not present any problems. The rishonim further explain that even though under ordinary circumstances we are concerned with the conflict of interest that may exist in cases like these, we see from here that we can trust reliable people, even if they take positions different than our own.