1) RETRACTING A "KINYAN"
OPINIONS: Rabah and Rav Yosef argue about when a Kinyan may be retracted. Rabah rules that a Kinyan may be retracted as long as the parties are still sitting. Rav Yosef rules that a Kinyan may be retracted as long as the parties are still discussing the transaction.
What type of Kinyan are Rabah and Rav Yosef discussing?
(a) The CHIDUSHEI HA'RAN quotes an opinion that explains that the Gemara refers only to a Matnas Shechiv Mera (the gift of a deathly ill person), because a sick person is likely to retract his words as long as they are talking about the topic of his estate. In contrast, in the case of a Matnas Bari (the gift of a healthy person), the person may retract his words only "Toch Kedei Dibur."
(b) The RASHBAM (DH Hachi Garsinan) explains that the Gemara clearly refers to the type of Kinyan which the Gemara discussed previously, a Matnas Bari or a Matnas Shechiv Mera. The Ran quotes this opinion in the name of most of the Rishonim, including the RAMBAM and RAMBAN. The Rashbam explains that one certainly may retract the Kinyan as long as the parties are still discussing the conditions of the transaction (the gift). The Rabanan understood that a person does not finalize the gift until he is satisfied with all of the conditions which he stipulates.
Does this reasoning apply to other forms of Kinyanim?
1. The ROSH (#5) writes that the Rabanan gave time for the parties to consider the conditions of the transaction only in the case of a Kinyan Sudar (which is often used to finalize a Matanah). However, "in other Kinyanim, such as where the person picks up, pulls, or gives over an object... a person cannot retract the Kinyan after Kedei Dibur." The Rosh clearly says that although there is no extended time period in which one may retract in the case of other Kinyanim, one may retract any Kinyan within the time of "Toch Kedei Dibur."
2. RABEINU YONAH initially agrees with the Rosh, but then he says that one can argue that when one takes possession of an object (Metaltelin) through Meshichah or one takes possession of land through Chazakah, the Kinyan is finalized with the action of the Kinyan, and it cannot be retracted even within "Toch Kedei Dibur."
Why, though, should Meshichah and Chazakah differ from all other forms of Kinyan? RAV GERSHON EIDELSTEIN shlit'a writes that Rabeinu Yonah clearly understands that the degree of finality of an act of Kinyan in the mind of the person depends on the specific type of Kinyan. For example, when the Gemara in Nedarim (87a) states that acts of Kidushin and Gerushin cannot be retracted even within "Toch Kedei Dibur," it is because the acts of Kidushin and Gerushin are so serious that a person deems them final at the moment he performs the act. Similarly, when one performs an act of Meshichah or Chazakah, such an act may be considered more final and conclusive than other forms of Kinyan. (Y. MONTROSE)
2) WHY DOES THE GEMARA MENTION THE CASE OF "MECHTZAH"?
QUESTION: The Gemara discusses the argument between Rabah and Rav Yosef, who disagree about when one may retract a Kinyan. The Gemara states that the Halachah follows the view of Rav Yosef in three cases: "Sadeh," "Inyan," and "Mechtzah" (see RASHBAM).
TOSFOS (DH v'Hilchesa) is bothered by the Gemara's inclusion of the case of "Mechtzah." The word "Mechtzah" apparently refers to Rav Yosef's statement in the case of the Gemara later (143a), in which a man says to his wife that he is bequeathing his possessions to her and her son. Rav Yosef rules that they split the possessions. However, in that case no one argues with Rav Yosef! Why does the Gemara need to mention that the Halachah follows Rav Yosef in that case, if no one argues?
(a) TOSFOS answers that while no one argues with Rav Yosef, Abaye did question his ruling. Although Rav Yosef answered the question, one might have thought that Rav Yosef's answer is not acceptable due to the fact that he became ill and forgot his learning. The Gemara therefore needs to teach that the Halachah indeed follows the view of Rav Yosef in that case as well.
(b) The CHIDUSHEI HA'RAN answers that while Abaye's question on Rav Yosef's ruling is not a reason to say that the Halachah is not like Rav Yosef, since the Halachah always follows the view of the teacher (Rav Yosef) when his student (Abaye) disagrees with him, there may be another reason why the Halachah should not follow Rav Yosef in that case. The Gemara may have had a tradition that Abaye's position was actually the position of Rabah, Rav Yosef's contemporary. This is why the Gemara here needs to teach that the Halachah indeed follows the view of Rav Yosef in the case of "Mechtzah."
(c) The RAMBAN answers that the Gemara's rule here, that the Halachah follows the view of Rav Yosef in three cases, applies only to arguments between Rav Yosef and Rabah. The Gemara includes the case of "Mechtzah" because of the case of "Sadeh." Since the Halachah follows the view of Rav Yosef in the case of "Sadeh," Abaye's question on Rav Yosef in the case of "Mechtzah" is no longer a question. This is why the Gemara here includes mention of the case of "Mechtzah."
(d) In his second answer, the Ramban explains that since the case of "Mechtzah" appears in the same Mesechta as the other two cases in which the Halachah follows Rav Yosef, the Gemara mentions the case of "Mechtzah" together with the other cases. (Y. MONTROSE)