1) REDEEMING HALF OF A "SEDEH ACHUZAH"
OPINIONS: The Gemara quotes the Mishnah in Erchin (25a) which teaches that if a field contains ditches deeper than ten Tefachim, or rocks higher than ten Tefachim, those areas are not calculated together with the field in accordance with the prescribed formula of "Zera Chomer Se'orim." (The Torah teaches (Vayikra 27:16) that one who consecrates his field (when the laws of Yovel are in force) may redeem his field by paying an amount calculated according to the formula of fifty silver Shekalim for every Chomer of barley seed that can be planted there.) The Gemara asks that although the value of the pits and rocks are not calculated with the field, they should become Hekdesh in their own right.
What is the Gemara's question? Why should those areas become Hekdesh if they are not considered part of the field?
(a) The RASHBAM (DH Likdeshu) explains that the fact that the ditches are not part of the field should not preclude them from being part of a Sedeh Achuzah. The Mishnah's statement that "they are not measured with it" (with the rest of the field) implies that they cannot have the Halachic status of a Sedeh Achuzah at all, and are not able to be redeemed separately in accordance with the formula of fifty Shekalim for every Beis Kor. The Gemara therefore asks why they cannot have the status of a Sedeh Achuzah.
TOSFOS (DH v'Amai) argues that this cannot be the Gemara's question. The Rashbam bases his understanding of the Gemara's question on the premise that if the ditches or rocks are considered a second Sedeh Achuzah, they should be able to be redeemed separately. However, the Gemara in Kidushin (21a) states that one can redeem half of a Sedeh Achuzah and use the prescribed formula for the redemption. This teaches that whether the ditches and rocks are considered part of the field or they are considered a separate field, they still should be redeemed with the prescribed formula for a Sedeh Achuzah. Why does the Gemara ask a question which implies that only because the ditches and rocks are considered separate from the field are they able to be redeemed individually?
(b) TOSFOS therefore explains that the Gemara's question is that even if the ditches and rocks are not considered part of the field, the Hekdesh should take effect on the entire area because the owner was Makdish his entire field. This implies that the ditches and rocks are considered a "field," albeit a separate field.
The RASHBA defends the Rashbam's opinion. When the Gemara in Kidushin says that one can redeem half of a Sedeh Achuzah, it does not mean that he may pay part of the redemption money and thereby instantly re-acquire the corresponding part of his field. Rather, it means that he may pay part of the value of the field in order to stop the transfer of that part of the field to the Kohanim when the Yovel year arrives. He does not receive that part of the field back until Yovel. Accordingly, whether the ditches and rocks are considered part of the field or a separate field has a practical consequence. If the entire land is considered one field, then if the former owner redeems part of the field before Yovel he may choose some of the ditches and rocks as well (if he so desires). If, however, the ditches and rocks are considered a separate field and the former owner pays towards the redemption of the primary field (without the ditches and rocks), he may not choose to redeem the ditches and rocks. This is the difference between whether the field is considered one unit or two units with regard to the redemption of a Sedeh Achuzah. (Y. MONTROSE)
2) "ONA'AH L'KARKA'OS" IN THE CASE OF THE SALE OF A "BEIS KOR AFAR"
OPINIONS: The Mishnah teaches that when one says that he is selling a Beis Kor of Afar and the measurement comes up short, the seller must compensate the buyer for the amount of land which he did not provide. If the land is found to be more than a Beis Kor, the buyer must give back that amount of land (or money) to the seller. In any event, the sale remains valid. The RASHBAM (DH Piches) asks that the Mishnah seems to contradict the ruling of Rava. Rava (90a) rules that whenever one specifies a precise measurement in a sale, the sale is rendered invalid when that measurement is off even by a small amount. Why does the Mishnah consider the sale valid?
(a) The RASHBAM answers that Rava's ruling applies only to Metaltelin (movable objects), not to land. People always seek to buy land, and thus they prefer to be compensated when they are overcharged than to have the purchase invalidated. Moreover, when the seller sells a Beis Kor of land, it is possible that he does not know the exact measurement of his land and he may be giving an estimated size. Accordingly, he is willing to add or subtract in order to consummate the deal.
The RAN questions the Rashbam's description of the difference between land and Metaltelin. The Gemara in Bava Metzia (56b) discusses the status of wheat seeds planted in the ground. It asks whether such seeds are considered land or Metaltelin. In the course of its discussion, the Gemara mentions Rava's ruling. If Rava's ruling applies only to Metaltelin, the Gemara there should not mention it in the context of its question, since the Gemara does not know whether the seeds have the status of Metaltelin or not. The Ran agrees, however, with the Rashbam's explanation that when a person sells a Beis Kor of land, he intends to ensure that the buyer receives a Beis Kor of land even if the specific land he is selling does not measure exactly a Beis Kor.
(b) TOSFOS (104a, DH Pachos) also has difficulty with the Rashbam's explanation of Rava's ruling. He quotes the RI who explains that Rava's ruling applies only to a person who measured a piece of land dishonestly, and the other party later took him to task for doing so. Such a sale is disqualified. However, if the seller is approximating the measure, he certainly has intent to supply a Beis Kor of land. Whether he will add or subtract land depends on the future measurement of the property.
(c) The SHITAH MEKUBETZES quotes an opinion which says that when the Mishnah states that the seller must compensate for missing land, and the buyer must compensate for extra land, it does not mean that compensation must be made against the will of the parties involved. If one of them chooses to opt out of the sale, he is entitled to do so. The reason why the Mishnah says only that the amount must be made up and it does not mention the fact that the sale can be canceled is that it is contrasting this case with the second case of the Mishnah, in which an understood approximation was given. In that case, an exact measurement is not necessary, since only an approximate size was stipulated when the property was sold ("Hen Cheser Hen Yeser" -- "whether it is a little less or a little more"). This is why the first case states only that the measurement is important, and not that the sale may be canceled if the measurement is not accurate.
(d) The RASHBA in Kidushin (42b) maintains that Rava does not say that the sale is "Batel" -- "invalid," but rather "Chozer" -- "goes back." The Rashba concludes that Rava means that cases of sales involving inaccurate measurements, weights, and numbers are never invalidated,* but rather the difference from the proper amount specified must be made up, whether in units or in price. According to the Rashba, there is no real difference between a sale of Metaltelin and a sale of land. In both cases, the sale is valid and the amount must be made up by supplying the difference in amount or by supplying the difference in price. (Y. MONTROSE)