1) THE REASONING OF SUMCHUS IN THE CASE OF THE WELL
OPINIONS: The Gemara quotes a Beraisa which discusses a case in which a person said, "Give a portion of my well to Ploni." Sumchus rules that Ploni receives at least one quarter of the well. If the giver says, "Give a portion of my well for filling up a barrel," Ploni receives no less than one eighth; "for a pitcher," he receives no less than one twelfth.
What is the reasoning behind Sumchus' ruling?
(a) The RASHBAM (DH Sumchus) says that Sumchus here is consistent with his well-known ruling (see Bava Kama 46a) that "Mamon ha'Mutal b'Safek Cholkin" -- when the ownership of money or property is in doubt, it is divided between the disputants. The word "portion" may mean "half," but it may also mean a tiny amount. Accordingly, when the owner of the well says, "Give a portion of my well to Ploni," there is a doubt about what he meant. Did he mean to give half of his well to Ploni, or a tiny portion of his well to Ploni? Since there is a doubt between a half and a bit, Sumchus applies his rule of "Mamon ha'Mutal b'Safek Cholkin" and Ploni receives one quarter of the well.
The Rashbam (DH l'Chavis) explains that this is the reasoning behind the other cases mentioned in the Beraisa. For example, in the case of "filling up a barrel," only one half of the standard-sized well is needed to fill up a barrel. Accordingly, there is a doubt whether the owner meant to give half of that amount, which is one quarter of the well, or whether he meant to give only a tiny portion. Sumchus rules that he receives one eighth of the well, or half of the amount in doubt. The Rashbam adds that this is also the understanding of RABEINU CHANANEL.
TOSFOS earlier (35a, DH u'Mai) writes that according to the Rashbam, the Gemara here implies that the Halachah follows the view of Sumchus. The Gemara here mentions the words of Sumchus as the answer to a question, and it gives no other opinion. The ROSH also says that the Rashbam rules like Sumchus. Tosfos cites many proofs, however, that that the Halachah does not follow the view of Sumchus. How, then, does Tosfos understand the reasoning for Sumchus' ruling in the Beraisa?
(b) TOSFOS explains that Sumchus' statement in the Beraisa here is unrelated to his ruling of "Mamon ha'Mutal b'Safek Cholkin." Rather, the reasoning behind his ruling here is that when a person uses the word, "Chelek" ("portion"), he presumably refers to one quarter of the maximum possible quantity being discussed. Therefore, when one says that Ploni should receive a "portion" of his well, he means one quarter. When he says that Ploni should receive "a portion of my well for filling up a barrel," he means a quarter of the portion of the well which fills up a barrel. Since half of the well fills up a barrel, a quarter of that amount if one eighth. This is also the opinion of the RIF.
(c) The ROSH agrees with the Rashbam that Sumchus here is consistent with his ruling of "Mamon ha'Mutal b'Safek Cholkin." Although this implies that the Halachah should follow the view of Sumchus, the Rosh agrees with Tosfos' proofs that the Halachah follows the view of the Rabanan who argue with Sumchus. However, in contrast to Tosfos, who says that the Rabanan agree with the ruling of the Gemara here, the Rosh says that because the Gemara here follows the opinion of Sumchus, its ruling cannot be the Halachah. (Y. MONTROSE)
2) THE STIPULATION THAT THE SELLER MAKES TO KEEP THE "DIYUTA ELYONA"
QUESTION: The Gemara earlier (63a) quotes Reish Lakish who says that when a person sells a house and stipulates that the "Diyuta Elyona" ("roof") remains his, the condition is valid. The Gemara asks, what is the Halachic significance of this statement? Even without such a stipulation, the upper level of the house is not included in the sale, as the Mishnah (61a) clearly states. It must be that the seller intends to retain some additional right for himself by making the apparently superfluous stipulation that the "Diyuta Elyona" remains his. What is that extra right? Rav Papa explains that the seller means that he reserves the right to build on top of the roof.
The Rishonim explain that Rav Papa does not mean that the seller reserves the right to build another floor on top of the attic, but rather that he reserves the right to rebuild the roof in case it (or the house) collapses.
The RASHBAM (DH Rav Papa) asks that this seems to contradict the Mishnah in Bava Metzia (117a) which clearly implies that a person who owns an upper floor of a house has the right to rebuild it if it collapses. Accordingly, Rav Papa has not answered the question of what the seller adds with his extra stipulation.
(a) The RASHBAM answers that in the case in Bava Metzia, two people divided a house which contained a ground floor and an upper floor, and they made an agreement that the owner of the ground floor will always have to let the owner of the upper floor rebuild in case his penthouse collapses. The Rashbam adds that even if they did not make an explicit condition to this effect, whenever two people divide a house in such a manner this condition is an inherent part of the division, even if it is not specified. In contrast, the case of the Gemara here involves a sale. In the case of a sale the seller of the house does not retain such a right towards the roof unless he explicitly specifies this condition. (A similar explanation is given by the RITVA.)
(b) TOSFOS (DH she'Im) answers that there is a difference between a "Diyuta" and an "Aliyah." The Gemara here refers to a Diyuta, roof, which is not so important. The owner of the roof does not have the automatic right to rebuild his Diyuta. The Mishnah in Bava Metzia refers to an Aliyah, an upper floor, which is important, and thus the owner automatically retains the right to rebuild.
RABEINU YONAH points out that there are two versions of Rav Papa's opinion in the Gemara. In the text of the Gemara used in Spain, the Gemara says that if he wants to build "an Aliyah" atop the house, he may do so. This text implies that the owner reserves the right to rebuild a top floor. According to this text of the Gemara, an Aliyah is the exact same thing as a Diyuta. This text effectively eliminates the answer of Tosfos. However, the text of the Gemara commonly used in France says only that if he wants to build on top of the house he may do so, and it does not mention the word "Aliyah." This text leaves room for Tosfos' interpretation that a Diyuta is not a top floor. (Rabeinu Yonah, however, agrees with the Rashbam's answer.) (Y. MONTROSE)