1) THE HUSBAND CANNOT MAKE A CONDITION IN THE GET WHICH UPROOTS A MITZVAH
QUESTION: The Mishnah (82a) quotes Rebbi Eliezer who ruled that if a man gives a Get to his wife and says that she is permitted to marry anyone except for a certain man, the divorce is valid. The Gemara cites a Beraisa which relates that after the death of Rebbi Eliezer, four elders -- Rebbi Yosi ha'Glili, Rebbi Tarfon, Rebbi Elazar ben Azaryah, and Rebbi Akiva -- questioned this Halachah.
Rebbi Tarfon asked that if a woman who receives such a Get would marry the brother of the man whom the Get prohibited her from marrying and her husband would die childless, the Get would uproot a Mitzvah from the Torah. RASHI (DH Oker) explains that the Get would uproot the Mitzvah of Yibum because the woman is forbidden to marry the brother of the second husband. Therefore, this Get does not provide the necessary condition of "Kerisus" (severance) which the Torah requires (Devarim 24:1); the Torah would not allow a "Kerisus" which uproots another Mitzvah in the Torah.
The Gemara later challenges Rebbi Tarfon's question. When the original husband gave the Get to his wife, he did not actually uproot the Mitzvah of Yibum. The Mitzvah becomes uprooted later merely as an indirect result of the giving of the Get. The Gemara suggests that the problem is that the husband made a condition to uproot the Mitzvah. The Gemara asks that this also is insufficient reason to disqualify the Get, because the woman did not have to marry the brother of the man who was forbidden to her.
The Gemara's question -- that the husband did not make a condition to uproot a Mitzvah because the woman did not have to marry the brother of the forbidden man -- implies that if he did make such a condition, the Get certainly would be invalid. If the husband would have said, "This is your Get on condition that you marry Reuven and you not marry his brother Shimon," the Gemara would have agreed with Rebbi Tarfon's opposition to Rebbi Eliezer's opinion.
However, why would such a statement even be considered a case of "Masneh Al Mah she'Kasuv b'Torah" (making a condition against what is written in the Torah)? The Gemara later (84b) teaches that if a man says to his wife, "This is your Get on condition that you should eat the meat of a Chazir," the Get takes effect if she eats the meat of a Chazir, and it does not take effect if she does not eat the meat. As Ravina explains there, that case is not considered a case of "Masneh Al Mah she'Kasuv b'Torah" because the man's condition is not certainly going to uproot a Mitzvah. Only when his condition certainly will uproot a Mitzvah (such as when a man marries a woman on condition that he will not be bound to provide her with food, clothing, and marital relations, all of which are obligations required by the Torah) does his condition not take effect. In contrast, when a man divorces his wife on condition that she should eat Chazir, he does not specify that she must eat it; she does not have to eat it if she does not want to. She may choose not to eat it, and she simply will not be divorced. The case of the Gemara here is identical to that case, and thus it should not be considered a case of "Masneh Al Mah she'Kasuv b'Torah." When the man says, "This is your Get on condition that you marry Reuven and you not marry his brother Shimon," she may choose not to marry Reuven. Why is the husband's statement considered an uprooting of the Mitzvah of Yibum?
ANSWER: The RASHBA answers that there is a difference between the case of a husband who uproots a Mitzvah through a condition he makes for the divorce and the case of a woman who fulfills a condition which involves a forbidden act. The Rashba quotes the Gemara in Chulin (140a) which says that there is no Mitzvah to send away a mother bird who is sitting on her eggs in an Ir ha'Nidachas, a city whose residents served Avodah Zarah, which must be destroyed together with all of its contents. One should not send the mother bird away because the Torah does not command one to "send the birds away to cause a stumbling block" ("Shalach l'Takalah"); since it is forbidden to benefit from the bird of an Ir ha'Nidachas, the Torah does not give a Mitzvah to send such a bird away, lest someone find it and benefit from it, unaware that it is forbidden.
Similarly, the Rashba explains that if the husband makes a condition in the Get that will lead to a violation of a Torah law later, the Get is not considered to be a valid form of "Kerisus." The Torah would not mandate a form of "Kerisus" that will later lead to a stumbling block. However, this is true only when the husband uproots the Mitzvah through the Get, since it is his Mitzvah to give the Get. However, when it is the wife who actively uproots the Mitzvah, his Get is deemed a fulfillment of "Kerisus" even though she uproots the Mitzvah in order to fulfill the condition to render the Get valid.
Accordingly, the giving of the Get on condition that she eat Chazir constitutes "Kerisus" because the husband did not uproot the Mitzvah himself. When a husband gives a Get on condition that she marry Reuven and not marry his brother Shimon, the woman's marriage to Reuven does not uproot any Mitzvah. Later, when she is unable to do Yibum with Shimon, she is not actively uprooting the Mitzvah. Rather, she is unable to do Yibum with Shimon because she is forbidden to him as a result of her first husband's original condition. Therefore, it is he who is considered the one who uproots a Mitzvah in the Torah. Moreover, if she were to do Yibum with Shimon her original Get would be rendered invalid, and thus retroactively she would be considered a married woman who re-married without a Get from her first husband, and any children from her other husbands would be deemed Mamzerim. Therefore, it is the husband who uproots the Mitzvah and is considered "Masneh Al Mah she'Kasuv b'Torah." (D. Bloom)

83b----------------------------------------83b

2) IS A TEMPORARY DIVORCE PERMANENT?
OPINIONS: Rava asked Rav Nachman a question: If a man gives a Get to his wife and says, "Today you are not my wife, but tomorrow you will be my wife," is the Get valid? RASHI (DH ha'Yom) explains that the husband specifies that the divorce will apply only today and not tomorrow; he made a "Shi'ur" in the Get -- he left something out of the divorce.
The Gemara explains that the question applies both according to Rebbi Eliezer and according to the Chachamim in the Mishnah (82a). In the case of the Mishnah, a man gives his wife a Get and says that he permits her to marry anyone except a certain man. Although Rebbi Eliezer maintains that this type of Get with a Shi'ur is valid, perhaps he validates it only when the husband permitted her permanently to the other men. Rava's question involves a case in which she was not permitted permanently to anyone. Moreover, even according to the Chachamim, the Shi'ur which Rava discusses may be valid because for the day on which she is divorced, she is divorced entirely and permitted to every other man with no restrictions. Once their relationship is severed for one day, she is divorced from him forever. Rashi (DH Paskah) explains that she will not be his wife again until he performs a new act of Kidushin with her. Therefore, the condition of temporary divorce which the husband attempted to make is meaningless, and the woman is divorced permanently.
The Gemara concludes that it is logical both according to Rebbi Eliezer and according to the Chachamim that she is divorced permanently from her husband with this Get.
However, this conclusion is difficult to reconcile with the Gemara later (85b-86a). The Gemara there states that one of the things that Rava (or, according to the Girsa of many Rishonim, Rav) instituted to write in a Get is that the husband divorces his wife "from today, forever." The Gemara (86a) explicitly states that Rava's requirement to write the word "forever" excludes his question to Rav Nachman in the Gemara here. The Gemara there clearly implies that a divorce that is not permanent is not valid.
How are these two Gemaras to be reconciled, and what is the Gemara's conclusion with regard to the question of Rava here?
(a) The RAMBAM (Hilchos Gerushin 8:9) writes, "If he made a condition and said, 'Today you are not my wife, and tomorrow you will be my wife,' she is not divorced even though the Get severs their relationship today. Therefore, one must write in a Get 'from today, forever.'"
The MAGID MISHNEH writes that the Rambam understands that the Halachah follows the ruling of the Gemara later (86a). The answer given by the Gemara here (that she is divorced permanently even though he said that the divorce will be valid for only one day) is not the Halachah.
(b) RASHI (86a, DH la'Afukei) interprets the Gemara here differently. He explains that the Halachah follows the conclusion of the Gemara here (83b) that once she is divorced for one day, she is divorced permanently. Nevertheless, Rava himself decreed (85b) that one should write "forever" in a Get so that no La'az (bad reputation) should be spread against the Get by people who do not know of Rava's law that she is divorced permanently whenever the Get takes effect for even one day.
RABEINU KRESKAS (end of 83b) agrees with Rashi. Moreover, he applies the logic of this Gemara to cases of monetary law. For example, if a person gives a field (both the land and the rights to the produce) as a gift to his friend for one day, the land becomes the permanent property of the recipient. Even though it was intended to be a temporary gift, once the original owner has relinquished his ownership for one day the field remains in the possession of the recipient until a new Kinyan is made, consistent with the logic of the Gemara here. (See AVNEI MILU'IM (28:53) who explains the comparison between the case of divorce and the case of the gift of the field.)
(c) The RAN (44a of the pages of the Rif) quotes both opinions and concludes that the woman is at least possibly divorced. The Magid Mishneh quotes an opinion that the woman is only possibly divorced (out of doubt), and adds that it is appropriate to be strict in any matter of forbidden relationships. This is also the ruling of the SHULCHAN ARUCH (EH 137:5). (D. Bloom)