QUESTION: The Gemara teaches that according to Rebbi Yosi b'Rebbi Yehudah, the verse of "Bas Eshes Avicha" (Vayikra 18:11) teaches that certain types of sisters are exempt from the Torah's prohibition of "Achoso," such as a sister born to a Shifchah or to a Nochris. The Gemara asks that perhaps the verse excludes a sister born from a union with a Chiyuv Kares. The Gemara answers that the verse cannot exclude such a sister because it states, "Moledes Bayis u'Moledes Chutz," which means that the prohibition of "Achoso" applies to both a sister from a union in which the father is allowed to remain married to his wife, and to a sister from a union in which the father is required to separate from his wife (because of an Isur Kares). In both cases, the prohibition of "Achoso" applies to the sister because the verse ends with the words, "Achoscha Hi" -- "she is your sister."

The Gemara asks that perhaps the verse of "Moledes Bayis u'Moledes Chutz" intends to teach that the prohibition applies to a sister born to a Shifchah or a Nochris, and the words "Achoscha Hi" refer to such a sister. The Gemara answers that this verse cannot include such sisters in the prohibition because the other verse already excludes them.

Why does the Gemara here cite the words "Achoscha Hi"? The words "Moledes Bayis u'Moledes Chutz," which include a sister from a union with a Chiyuv Kares, appear in Vayikra 18:9, where the words "Achoscha Hi" do not appear! The words "Achoscha Hi" appear in a later verse (Vayikra 18:11) which discusses "Bas Eshes Avicha." The Gemara should ask instead that the sister from the union of "Moledes Bayis u'Moledes Chutz" is prohibited because the verse says about her, "Lo Segaleh Ervasah." (MELO HA'RO'IM)

(The words "Achoscha Hi" appear to be the original Girsa in the Gemara, as the Rishonim cite the Gemara with those words. See RIVAN.)

ANSWER: According to Rebbi Yosi b'Rebbi Yehudah, the later verse which says "Bas Eshes Avicha" and which ends with "Achoscha Hi" does not teach an Isur. Rather, it excludes a certain type of sister from the Isur. The words "Achoscha Hi" at the end of the verse teach that the limitation at the beginning of the verse is not all-inclusive; that is, it is a "limited limitation," which means that only a woman who does not fit at all into the category of "Bas Eshes Avicha" is not considered one's sister with regard to the Isur. If, however, she fits in some way into the category of "Bas Eshes Avicha," the verse does not intend to exclude her from the Isur. Thus, the phrase "Bas Eshes Avicha" is the limitation (Mi'ut), while the phrase "Achoscha Hi" limits the limitation (it minimizes the Mi'ut). (Although the verse "Moledes Chutz" is also used to minimize the Mi'ut, without "Achoscha Hi" one would have learned that "Moledes Chutz" teaches other laws, such as the law which Tosfos (3a, DH Bito) cites in the name of the Targum.)

Accordingly, when the Gemara quotes the words "Achoscha Hi," its intention is to add that one should not exclude all types of sisters who come from unsanctioned unions; one type of sister that is included in the Isur is the one mentioned in the earlier verse of "Moledes Bayis u'Moledes Chutz" -- a sister from a union with a Chiyuv Kares.

QUESTIONS: The Mishnah discusses a case of a man who betrothed (with Kidushin) one of two sisters and forgot (or did not know) which one. If the man dies childless and has only one brother, that brother must do Chalitzah with both women. If he has two brothers, one brother does Chalitzah with one woman, and the other brother may do Yibum with the other woman.

The Gemara asks that the teaching of the Mishnah seems obvious. The Gemara answers that the teaching of the Mishnah is necessary when the man has two brothers, in which case the first brother must do Chalitzah with the first woman and only afterwards may the second brother do Yibum with the second woman. Yibum may not be done first, because that sister might not be the one who was betrothed, in which case the brother who does Yibum with her transgresses the prohibition against marrying the sister of one's Yevamah ("Achos Zekukaso").

(a) Why does the Gemara say that this Chidush is inferred only from the Mishnah's second case, when the man who dies has two brothers? The same principle is necessary in the first case, when the man who dies has only one brother: the surviving brother must do Chalitzah with both women and may not do Yibum with either one, because if he does Yibum with the first he might be transgressing the Isur of "Achos Zekukaso," and if he does Yibum with the second he might be transgressing "Achos Chalutzaso." (ARUCH LA'NER)

(b) Why does the Gemara say that had there been no Isur of "Achos Zekukaso," one would have assumed that the first brother may do Yibum with the first woman and then the second brother may do Chalitzah with the second woman? The Gemara should have said that one would have thought that both brothers may do Yibum with the two women! Once Yibum or Chalitzah has been done with the first sister, the second one certainly may do Yibum, as the Mishnah indeed rules in this case: the first does Chalitzah and the second may do Yibum. (TOSFOS REBBI AKIVA EIGER on the Mishnah)

(a) The ARUCH LA'NER answers the first question. He explains that the Gemara's intention is to show that the Mishnah follows the view of "Yesh Zikah" and therefore teaches that one of the sisters is forbidden because of "Achos Zekukaso." This inference can be made only from the second case in the Mishnah, not from the first. In the first case (when there is only one brother), the brother may not do Yibum with the first sister even according to the view of "Ein Zikah." By doing Yibum with her, he might be forfeiting the Mitzvah of Yibum ("Bitul Mitzvas Yevamim") since the other sister may be the real Yevamah. By taking the first sister, he prohibits himself to the second sister (who might be the real Yevamah) and thereby forfeits the Mitzvah of Yibum.

The Gemara proves "Yesh Zikah" only from the second case of the Mishnah, when there are two brothers. Even if the first brother does Yibum with the first sister when the second sister is the real Yevamah, that brother does not forfeit the Mitzvah of Yibum because the other brother may do it.

(The teaching of the Mishnah here does not contradict the Gemara earlier (18a) which states that one may not cause even a possibility of forfeiting the Mitzvah of Yibum. The Gemara there teaches that even when there is another brother who can do Yibum, perhaps that brother will die before he does Yibum. The case of the Mishnah here is different, because in this case there are two doubts (a Sfek Sfeika): perhaps the brother will not die, and even if he does die perhaps the woman with whom the first brother did Yibum was the real Yevamah. One is not prohibited from marrying a woman when there are two reasons to doubt whether he is forfeiting the Mitzvah of Yibum (see Yevamos 27b).)

This explains why the Gemara proves only from the second case of the Mishnah that "Yesh Zikah" (and "Zekukah k'Kenusah"). This also explains why Rashi, throughout the Mishnah, explains that the Mishnah follows the opinion that "Yesh Zikah," and he does not consider the possibility that the Mishnah maintains "Ein Zikah" but one may not forfeit the Mitzvah of Yibum.

(b) The Aruch la'Ner's approach does not resolve Rebbi Akiva Eiger's question. Perhaps another approach may be suggested which will answer both questions.

The Gemara does not take into account the possibility that the Mishnah's reason (for requiring the first brother to do Chalitzah before the second brother may do Yibum) is the prohibition against forfeiting the Mitzvah of Yibum. The Gemara understands that since only one of the sisters is actually the Yevamah, the other sister has the status of only a Safek "Achos Zekukaso." There is no prohibition against forfeiting a Safek Mitzvah of Yibum by marrying a woman who might be the sister of the Yevamah. After all, the Chachamim are lenient in any case of a Safek Isur d'Rabanan (in this case, the Isur d'Rabanan is the Isur against being Mevatel the Mitzvah of Yibum). Rather, the only reason why the Chachamim were stringent in the case of the Mishnah, a case of a Safek Yevamah, is that the Safek Isur of "Achos Zekukaso" or "Achos Chalutzaso" is more severe than an ordinary Isur d'Rabanan, as the Rishonim write. The Isur of "Achos Zekukaso" resembles that of "Achos Ishto," which is an Ervah d'Oraisa, and thus the Chachamim treated this Safek more stringently than an ordinary Safek Isur d'Rabanan.

If the Gemara knows that the Mishnah's reason for prohibiting both brothers from doing Yibum is because of the Safek Isur of "Achos Zekukaso," why does the Gemara not prove from the first case in the Mishnah, which says that when there is only one surviving brother he may not do Yibum but must do Chalitzah with both women, that "Yesh Zikah" and that there is an Isur against marrying "Achos Zekukaso"? The fact that the Mishnah prohibits the brother from doing Yibum with the first sister proves that there is an Isur of "Achos Zekukaso," because, otherwise, he should be permitted to marry the first sister (as the Aruch la'Ner asks).

Perhaps the reason why the Gemara does not prove the Isur of "Achos Zekukaso" from the first case of the Mishnah is that it is obvious that the brother becomes prohibited from doing Yibum with the second sister once he does Yibum with the first because of the Isur d'Oraisa of "Achos Ishto." The only question is why the Mishnah does not permit the brother to do Yibum with the first sister and then do Chalitzah with the second. Perhaps the reason why the Mishnah does not permit this procedure is that the brother might confuse the order and do Chalitzah first and then do Yibum, in which case he will be marrying "Achos Chalutzaso," the sister of the woman with whom he did Chalitzah who is forbidden to him. (Rashi mentions such a Gezeirah earlier on 18a, DH l'Olam Ein Zikah.) This explains why the Gemara does not prove from the first case of the Mishnah (in which one brother is required to do Chalitzah with both sisters) that there is an Isur of "Achos Zekukaso." The Gemara can prove it only from the second case, in which there are two brothers. In that case, the Mishnah allows one brother to do Chalitzah and the other to do Yibum, and nevertheless it does not allow the first brother to do Yibum before the Chalitzah is done with the other sister.

This approach may answer Rebbi Akiva Eiger's question as well. Rebbi Akiva Eiger asks why, in the first stage of the Gemara when it assumes that there is no Isur of "Achos Zekukaso," the Gemara does not say that both brothers may do Yibum with both sisters. The answer is that the Gemara reasons that it is not permitted for both brothers to do Yibum with the two "Safek" sisters who fell to Yibum from the deceased brother, due to a Gezeirah for a case of two women who were actually married to the deceased brother. That is, if the two brothers would be permitted to do Yibum with the two sisters (when only one of them is the real Yevamah), people will not be aware that it is because one of them is not a Yevamah at all; they will mistakenly permit two brothers to do Yibum with two Yevamos who were married to one man. (This Gezeirah is found in other situations, as described on 31b.)

Accordingly, it is clear that the Mishnah does not permit both brothers to do Yibum for that reason (the Gezeirah). The Gemara asks, however, that if the Mishnah applies all of these Gezeiros to prohibit Yibum in the various cases, why, in the second case of the Mishnah, does it permit the first brother to do Chalitzah with the first sister and the second brother to do Yibum with the second sister? The Mishnah should have permitted the procedure in the opposite order -- the first brother should do Yibum with the first sister, and then the second brother should do Chalitzah with the second sister. This order would prevent people from mistakenly assuming that in a case in which there is only one brother, he may do Chalitzah with the first sister and then do Yibum with the second (in which case he would transgress the Isur of "Achos Chalutzaso"). If the Mishnah indeed is concerned for such mistakes, it should have specified that in a case of two surviving brothers, the first should do Yibum and only afterwards may the second do Chalitzah, so that even if a single brother learns from that case that he, too, may do Yibum with the first sister and then do Chalitzah (as opposed to doing Chalitzah with both), he will at least not transgress an Isur as severe as "Achos Chalutzaso," but only the less-severe Isur of "Achos Zekukaso." ("Achos Zekukaso" is less of an Isur than "Achos Chalutzaso" because after he does Chalitzah with the second sister it removes the Zikah and, retroactively, when he married the first sister there was no Isur of "Achos Zekukaso". If, however, he does Chalitzah first and then Yibum with the second sister, he will be living with his "Achos Chalutzaso" and the Isur will never be removed.)

Since the Mishnah requires that the first brother do Chalitzah and the second do Yibum, it is apparent that the requirements of the Mishnah are not due to Gezeiros at all, but are based on preventing a transgression of the Isur of "Achos Zekukaso." (M. Kornfeld)