The Gemara points out that Rav Yehudah, who maintains "Yesh Zikah," did not
say so explicitly. Rather, his opinion is inferred from a Halachic ruling of
his. Rav Yehudah says that if a Yevamah dies before doing Yibum, the Yavam
may not marry her mother. The reason is because "Yesh Zikah" -- there is a
bond of Zikah connecting him to the Yevamah, and just like one may not marry
the mother of one's wife, one may not marry the mother of one's Yevamah. The
Gemara explains that the reason why Rav Yehudah did not say simply "Yesh
Zikah" is because had he said "Yesh Zikah" we might have thought that there
is Zikah only when both the Yevamah and Yavam are alive (and only when the
Yevamah is still alive would it be prohibited for the Yavam to marry her
mother), but after the Yevamah has died there is no Zikah and the Yavam could
marry the Yevamah's mother. We might have thought that after her death, any
bond of Zikah is removed *retroactively* since he can no longer do Yibum or
Chalitzah with her. Rav Yehudah teaches that not only is there Zikah, but the
Zikah is not removed retroactively.
(a) RASHI (17b, DH v'Leima) explains that if a man dies childless and his
wife falls to two brothers for Yibum, and then one of the brothers is
Mekadesh (with Kidushin, but not yet with Nisu'in) the sister of the Yevamah,
thereby making the Yevamah an Ervah to him ("Achos Ishto"), we tell that
brother to delay doing Nisu'in with the sister because she is "Achos
Zekukaso," the sister of the woman who has a bond of Zikah with him and is
thus Asur to him mid'Rabanan. Rather, he should wait until the other brother
does Yibum (or Chalitzah), and then, says Rashi, "the Zikah is removed" and
the first brother may now fully marry the Yevamah's sister. The Gemara (18b)
explains that this follows the opinion of Rav Yehudah that "Yesh Zikah" and
that is why the sister of the Yevamah ("Achos Zekukaso") is Asur to the
brother.
However, the Gemara just taught that even when the Yevamah dies, the Yavam
remains Asur to her mother, because the Zikah does not fall away. Likewise,
in the case that Rashi discusses, when the other brother does Yibum, the
first brother should remain Asur to the sister of the Yevamah even after the
second brother does Yibum or Chalitzah, just like one is Asur to the sister
of a woman that one divorced!
It is clear that doing Yibum removes the Zikah retroactively from the other
brothers (and from the Tzaros as well). Even though the Gemara earlier (10b)
says that, according to Rebbi Yochanan, the brother who does Yibum or
Chalitzah acts as the Shali'ach on behalf of all of the brothers,
nevertheless it is not as if the other brothers are actually performing the
Yibum; rather, the brother who does Yibum does it *for himself*, for the
other brothers, so that the Zikah is removed from them -- and from the Tzaros
of the Yevamah -- even retroactively.
When our Gemara says that Zikah is not removed retroactively, it means that
only Yibum or Chalitzah can remove the Zikah retroactively from the other
brothers and the other Tzaros, but not *death*. The death of the Yevamah or
the Yavam cannot remove the Zikah retroactively (because had the person been
alive he might have opted to do Yibum or Chalitzah).
(b) According to the RASHBA, all of the questions of the Gemara (18a) --
which it asks when it challenges the view of Rav Yehudah who says that it is
Asur for a brother to marry the mother of a Yevamah after the Yevamah dies --
are not intended to prove that Rav Yehudah is incorrect and "Ein Zikah."
Rather, the Gemara agrees that "Yesh Zikah," but it is trying to prove that
Zikah *is* retroactively removed if the Yavam or Yevamah dies.
If the Zikah is removed retroactively, then the Mishnah (17a) works out
smoothly. The Gemara questions the opinion that says "Yesh Zikah" from the
end of the Mishnah. The Mishnah implies that if Levi is born before Shimon
does Yibum, and Shimon dies without doing Yibum, Levi does Yibum or Chalitzah
with Shimon's wife.
Asks the Gemara, why do we not say that Shimon's wife is a "Tzaras Ervah
b'Zikah" (the Tzarah of a woman who is an Ervah through Zikah), since the
wife of Reuven who was Asur to Levi (because of "Eshes Achiv she'Lo Hayah
ba'Olamo") was Zekukah to Shimon? The Gemara means to prove from this that
the Zikah is removed retroactively when Shimon dies. If the Zikah was removed
retroactively, then Shimon's wife was *not* a "Tzaras Ervah b'Zikah," since
there was no Zikah, as it was removed from her retroactively when Shimon
died.
Similarly, the Gemara asks a contradiction in the opinion of Rebbi Meir, who
in one case says that if Levi was born before Shimon died and Shimon died
without doing Yibum to Reuven's wife, then Levi is allowed to do Yibum with
Shimon's wife, which means that Shimon's wife is not considered a "Tzaras
Ervah b'Zikah" to Levi; we do not view the Zikah (of Reuven's wife to Shimon)
as making her a Tzarah of Shimon's wife. On the other hand, Rebbi Meir says
that if two sisters fall to Yibum from two different brothers, the brothers
must do Chalitzah and are not allowed to do Yibum. This implies that each
woman is considered "Achos Zekukaso" and is Asur to each brother, and that is
why they cannot do Yibum.
Here, too, explains the Rashba, the Gemara is trying to prove that Zikah is
retroactively removed when the Yavam dies. That is why, in the first case,
when the Yavam (Shimon) died, there was no Zikah and Shimon's wife was not a
"Tzaras Ervah" through Zikah. But in the second case, none of the Yevamim
died, and since Chalitzah or Yibum will be done, the Zikah remains in force
and the two sisters are Asur to the brothers because of "Achos Zekukaso" and
therefore they must do Chalitzah.
(c) Although our Gemara answers its questions (on Daf 18a) and rejects the
proofs that Zikah is removed retroactively, the OR SAME'ACH (ibid.) shows at
length that the Yerushalmi in many places says that this initial suggestion
of our Gemara -- that Zikah is removed retroactively even by the death of the
Yevamah or Yavam -- is true and conclusive. That is, the Yerushalmi
maintains, contrary to the Bavli, that Zikah *is* removed retroactively after
the death of the Yavam or Yevamah.
RAV MEIR ARIK (in TAL TORAH, Yerushalmi Yevamos 1:1, 3b) offers a beautiful
explanation for a Yerushalmi in Kidushin (3:5, 31b) based on this. The
Mishnah there (see Kidushin 62a, Yevamos 92b) says that if a man says to a
married woman, "I am hereby Mekadesh you [beginning from a future date] after
your *husband dies*" or "after your *Yavam does Chalitzah* with you," the
Kidushin does not take effect because he is trying to be Mekadesh a "Davar
she'Lo Ba la'Olam." (That is, he is trying to be Mekadesh a woman who cannot
accept Kidushin until a future moment, since she is presently married or
Zekukah to another person).
The Gemara in the Yerushalmi says that the Mishnah specifically mentions that
the man said to the woman "after your Yavam does Chalitzah with you," but
*not* "after your Yavam dies," because in such a case the Kidushin *would*
take effect after the Yavam dies (since it was possible for the Kidushin to
take effect even *before* he dies).
What is the difference between after the Yavam does Chalitzah and after the
Yavam dies? In both cases, the woman at the time of the Kidushin is a "Davar
she'Lo Ba la'Olam" and cannot accept Kidushin (as the Bavli indeed says in
both cases)!
The answer is that the Yerushalmi maintains that the Zikah is removed
retroactively after the death of the Yavam. Thus it turns out that the
Yevamah was able to become married to someone else all along, although she
didn't know it at the time, and since it was possible to be Mekadesh her at
the time, she was not a "Davar she'Lo Ba la'Olam." If the Yavam performs
Chalitzah, though, the Zikah is not removed retroactively and therefore
Kidushin cannot be performed with her until after the Chalitzah! (This shows,
also, that the Zikah is not only removed retroactively with regard to the
bond between the Yevamah and the Yavam. Even with regard to the prohibition
for the Yevamah to marry out it is removed.)