1) A "SHOMERES YAVAM" WHO REFUSES TO DO YIBUM
QUESTION: Shmuel says that an Arusah who refuses to marry her husband is considered a rebellious wife ("Moredes") and her Kesuvah is reduced until she agrees to marry him. Shmuel says further that a Shomeres Yavam who refuses to have anything to do with her Yavam is not considered a rebellious wife and her Kesuvah is not reduced.
The Gemara questions Shmuel's ruling from a Beraisa that states that even a Shomeres Yavam is considered a rebellious wife if she refuses to have anything to do with her Yavam. Rebbi Yochanan answers that Shmuel refers to a Yavam who wants to do Chalitzah and the Shomeres Yavam refuses, while the Beraisa refers to a Yavam who wants to do Yibum and the Shomeres Yavam refuses. When the Yavam wants to do Chalitzah, the woman is considered a Moredes for refusing, but not when he wants to do Yibum and she refuses.
RASHI explains the logic of Rebbi Yochanan's statement. Rebbi Yochanan follows the Mishnah Acharonah that states that it is preferable to do Chalitzah than to do Yibum, because a person might not have pure intentions when he does Yibum.
The Gemara rejects Rebbi Yochanan's answer and asserts that there should be no difference between Yibum and Chalitzah. If the Yavam claims that no other woman will marry him because he has not yet become exempt from marrying his Yevamah, he should be able to force her to do either Yibum or Chalitzah with him. If, on the other hand, the Yavam is able to find a different wife, he should not be able to force the Yevamah to do either Yibum or Chalitzah!
Because of this question, the Gemara concludes that Shmuel and the Beraisa both refer to a Yavam who wants to do Yibum. The Beraisa does not contradict Shmuel because the Beraisa follows the Mishnah Rishonah that says that Yibum is preferable to Chalitzah (and therefore the Yavam may force the Yevamah to perform Yibum), while Shmuel follows the Mishnah Acharonah that says Chalitzah is preferable because the Yavam might not have pure intentions (and therefore Beis Din does not force the Yevamah to do Yibum just because the Yavam wants to). It seems that the Gemara rejects Rebbi Yochanan's difference between a Yavam who wants to do Yibum and a Yavam who wants to do Chalitzah.
There are a number of questions with Rashi's explanation for the way the Gemara deals with Rebbi Yochanan's statement.
(a) The Gemara says that in a case where the Yavam will be able to find a different wife if he does not do Chalitzah with the Shomeres Yavam, Beis Din should not force the Shomeres Yavam to do Chalitzah. Why should Beis Din not force her? After all, there is a Mitzvah to do Chalitzah, and the Mishnah Acharonah maintains that the Mitzvah of Chalitzah is even more important than the Mitzvah of Yibum. Just as Beis Din forces her to do Yibum according to the Mishnah Rishonah, Beis Din should force her to do Chalitzah according to the Mishnah Acharonah! (RITVA in the name of RABEINU TAM)
Indeed, TOSFOS (DH Mai) explains that according to the Mishnah Acharonah, Beis Din does force the Yevamah to do Chalitzah.
(b) Why does the Gemara say, according to Rebbi Yochanan, that Beis Din does not force her to do Yibum "because the Yavam is able to find a different wife without doing Yibum"? There is a better reason for why she is not forced to do Yibum: Rashi writes that Rebbi Yochanan follows the Mishnah Acharonah which says that Yibum is to be avoided because the Yavam might have impure intentions. Accordingly, Beis Din certainly should not force a man to do Yibum! (TOSFOS DH Mai)
ANSWERS:
(a) Apparently, Rashi means that although Beis Din forces a man to do Yibum according to the Mishnah Rishonah because the Mitzvah of Yibum is greater than the Mitzvah of Chalitzah, nevertheless according to the Mishnah Acharonah (which maintains that Chalitzah is greater than Yibum) the Yavam cannot force the Yevamah to do Chalitzah.
The reason why he cannot force her to do Chalitzah is based on the way Rashi understands the Mitzvah of Chalitzah. Rashi explains that Chalitzah, in contrast to Yibum, is not a Mitzvas Aseh which is incumbent upon the Yavam to do. Rather, it is merely a way to permit the Yevamah to remarry when Yibum is not performed. It is done solely for the benefit of the Yevamah. Therefore, if the Yevamah does not want to perform Chalitzah and is prepared to remain an Agunah and never remarry, she cannot be forced to perform Chalitzah. In such a case, there indeed is no reason to perform Chalitzah at all.
Although the Mishnah in Bechoros (13a) compares the Mitzvah of Chalitzah with the Mitzvah of Yibum and refers to both as Mitzvos Aseh (when it says that the "Mitzvah of Chalitzah is greater than the Mitzvah of Yibum"), Rashi understands that the Gemara calls Chalitzah a Mitzvah only because it is an act which the Torah prescribes in order to permit a Yevamah to remarry. Since she is required to do Chalitzah in order to remarry (if she does not do Yibum), the act is called a Mitzvah. (That is, Chalitzah is a Mitzvah in the same sense that Gerushin (divorce) is counted as Mitzvah.) When the Mishnah there says that Chalitzah is greater than Yibum, it means that it is greater in the sense that it avoids the problem which arises if the Yavam performs Yibum with impure intentions.
Tosfos -- who says that Beis Din forces the Yevamah to do Chalitzah according to the Mishnah Acharonah -- seems to maintain that Chalitzah is a positive Mitzvah like Yibum, and therefore Beis Din may force her to do Chalitzah.
According to this explanation, Rashi is consistent with his own opinion as expressed elsewhere. The Mishnah in Sanhedrin (18a) teaches that a king does not perform Chalitzah if a Yevamah falls to him, and the king's wife does not do Chalitzah if the king dies with no children. Similarly, a king does not perform Yibum with his brother's wife, and the king's wife does not perform Yibum with the king's brother.
It is clear why the king does not do Yibum or Chalitzah with his brother's wife; there is a Mitzvah to uphold the honor of a king, and doing Yibum with his brother's wife to "build the house of his brother," or having his brother's wife spit in front of him when she does Chalitzah, would be a disgrace to the honor of the king (Rashi). Similarly, it is clear why a king's wife may not do Yibum with her husband's brother. The king's brother is a Hedyot (a non-king), and a Hedyot is prohibited from marrying the wife of a king after the king dies. However, why does the Mishnah there say that Chalitzah may not be done with a king's wife after the king dies? There is nothing shameful with the king's brother doing Chalitzah with the king's wife.
RASHI in Sanhedrin (19b, DH v'Lo Choltzin) explains that Chalitzah is not performed with the wife of a king because she is prohibited from remarrying. Rashi there implies that there is no point in performing Chalitzah if it will not enable the woman to remarry! Rashi here follows that approach.
(The TIFERES YISRAEL in Sanhedrin suggests that Rashi might not mean that there is no point in doing Chalitzah if the woman will not remarry. Rather, Rashi means that the Chachamim instituted that she not perform Chalitzah lest she think that she is permitted to remarry when she really is prohibited from remarrying because she is the widow of a king. However, the straightforward intent of Rashi seems to be that a woman who does not intend to remarry has no Mitzvah to perform Chalitzah, as explained above. The question of whether Chalitzah is a Mitzvah in its own right may be related to the discussion of the Yerushalmi (Yevamos 1:1) about whether Chalitzah is "an exemption from Yibum, or a type of Kinyan.")
(b) Why does the Gemara not say that in a case where the Yavam wants to do Yibum, the woman is not considered a Moredes (and she is not forced to do Yibum) because Yibum is looked upon unfavorably according to the Mishnah Acharonah? The answer appears to be as follows. The Gemara means that if the Yavam insists on doing Yibum and she refuses to do either Yibum or Chalitzah, Beis Din forces her to do Chalitzah in order to enable him to marry another wife. Although the Yavam insists on doing Yibum, since his purpose is to be able to marry another wife Beis Din forces her to do Chalitzah so that he can get married. (See Tosfos DH Mai Shena, who rejects this approach.)

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