Baalas Tenaim: When Does Zika L'Yibum Apply and When Does an Ervah Exempt the Tzarah?

This shiur on Yevamos 6a presents a complex analysis of when a woman is considered an ervah for purposes of exempting her tzarah from yibum, focusing on the case of a baalas tenaim—a woman whose status as eishes ish to the yavam depends on a conditional restriction. Rabbi Zweig begins by distinguishing between two types of exemptions from yibum: (1) when a woman herself is an ervah b'shas nefilah (at the moment the husband dies), making her categorically outside the parsha of yibum, and (2) when zika l'yibum subsequently falls off due to a prohibition that arises later. The first creates a total exemption; the second raises the question whether the zika can "come back" if the impediment is removable. The shiur examines Tosfos on daf 6a and daf 17a, showing an apparent contradiction. On daf 17a (tes zayin), Tosfos holds that when there is initially a zika l'yibum and then the woman becomes forbidden (such as through mekadesh her to create an issur eishes ish), if that prohibition can be removed by giving a get, then the zika never truly goes off—"anything that can come back doesn't go off." But on daf 6a (yud), Tosfos discusses a case where the woman is already an eishes ish to the yavam through a conditional neder at the moment of nefilah, and Tosfos holds she does not exempt the tzarah because "she's not dumi l'achos isha." Rabbi Zweig reconciles these Tosfos by arguing that daf yud is discussing a situation where b'shas nefilah there is no zika at all—she is already an eishes ish—so the question is not whether zika can be restored but whether she ever had zika to begin with.