1) THE ALLOWABLE MARGIN OF ERROR IN THE SALE OF A "BEIS KOR"
QUESTION: The Gemara quotes a Beraisa which states that when one says that he is selling "a Beis Kor," "like a Beis Kor," or "a little less or a little more than a Beis Kor," in each of these cases he is allowed a margin of error of one quarter of a Kav per every Se'ah (there are thirty Se'ah in a Beis Kor; see RASHBAM to 102b, DH ha'Omer).
(This Halachah also applies to the buyer, who may keep up to one quarter of a Kav extra per Se'ah. For the purposes of brevity, here we will discuss the case from the viewpoint of the seller.)
The Gemara concludes that this Beraisa provides proof that when a person says that he is selling a Beis Kor, he approximates the size of the field that he sells and does not intend to sell exactly a Beis Kor.
TOSFOS (DH Ela) has difficulty with the Gemara's conclusion. The Mishnah earlier (102b) says that ditches less than ten Tefachim deep are included in the sale of a field. The Gemara there (103a) quotes Rebbi Yitzchak who says that only up to four Kav of such ditches are included in the sale, and not more. If the Gemara here means that one is allowed a margin of error of a quarter of a Kav per Se'ah, and there are thirty Se'ah in a Beis Kor, then the seller may withhold up to seven and a half Kav of land from the buyer! Why does Rebbi Yitzchak say that he may include only up to four Kav of ditches?
(a) TOSFOS (according to the MAHARSHAL's understanding) answers that when Rebbi Yitzchak says that only up to four Kav of ditches may be included, he means that only up to four Kav may be included in the amount of land which must be provided in the sale, after the seven and one half Kav of "leeway" area has been taken into account.
The AYELES HA'SHACHAR asks that according to Tosfos, would a seller be permitted to say that he is selling a field which is a "Beis Kor" when he knows that the field contains seven Kav less than a Beis Kor? Are the words "Beis Kor" in such a case considered an acceptable approximation of the size of the field, or are his words considered a lie? The Ayeles ha'Shachar does not answer this question.
(b) Tosfos quotes the RASHBA who says that when the Gemara says that one has leeway of up to seven and one half Kav, it refers to a case where the buyer and seller saw the area being sold and agreed that this was the Beis Kor referred to in their deal. If they find that their estimation of its size is inaccurate, they are allowed up to one quarter of a Kav of a margin of error. Rebbi Yitzchak, however, refers to a case in which the Beis Kor which was purchased was not seen. In such a case, there is no reason to allow the seller to supply one quarter of a Kav less than the measurement mentioned in the sale, since the buyer understood that he was buying a full Beis Kor. It is in this case that Rebbi Yitzchak rules that only up to four Kav of ditches may be included in the sale.
(c) The ALIYOS D'RABEINU YONAH answers that the case in which up to four Kav is acceptable refers to a person who sells one Beis Kor out of a large piece of property. Since he has a lot of land from which to choose, he has the right to give land which contains up to four Kav of ditches. The Gemara, in contrast, is talking about a b'Di'eved situation in which the seller does not actually have a full Beis Kor. In such a situation, the buyer still must take the field if there is only one quarter of a Kav per Se'ah missing. Rebbi Yitzchak would agree that the buyer certainly must also take a full Beis Kor when there is no more land left, even if it has up to seven and a half Kav of ditches. (Y. MONTROSE)
2) WHEN THE SELLER GETS BACK LAND
OPINIONS: The Mishnah (103b) teaches that when the size of a field is estimated at a Beis Kor (thirty Se'ah) at the time it is sold, both the buyer and the seller must agree to accept a loss or a gain of one quarter of a Kav per Se'ah. This means that if there is up to one quarter of a Kav of extra land per Se'ah, the buyer may keep that land. If the extra land is more than one quarter of a Kav per Se'ah, "the seller has the upper hand in a case where he gave nine extra Kav in a field." Rav Huna and Rav Nachman disagree about the intent of the Mishnah. Rav Huna explains that the Mishnah means that if the land contains nine extra Kav including the one extra quarter of a Kav per Se'ah that a buyer normally is allowed to keep, all of the extra land goes back to the seller. Rav Huna understands that the seller would never intentionally add so much land, which itself is considered a proper field. Therefore, in a case in which an area of two Kor (60 Se'ah) of land was sold and one quarter Kav was left per Se'ah, all of the extra land returns to the seller.
Rav Nachman disagrees and explains that every Kor may contain up to seven and a half extra Kavin. If there is more than nine Kav, the land returns to the seller. What does Rav Nachman mean to say?
(a) The RASHBAM (DH v'Iy) explains that Rav Nachman means that if there is even a small bit more than a quarter of a Kav per Se'ah, and altogether there is more than nine extra Kav, all of the extra land goes back to the seller. Accordingly, whether the extra land returns to the seller depends on the size of the land being sold. If two Kor are sold and there is one quarter of a Kav extra per Se'ah, all of the extra land goes to the buyer unless the extra land is slightly more than one quarter of a Kav per Se'ah. If one Kor is sold and there is one quarter of a Kav extra per Se'ah, the buyer keeps the land. If, however, in this second case there is one Kav and a half more of extra land, all of the land goes back to the seller. If there is more than seven and a half Kav but less than nine Kav extra, the buyer must compensate the seller for all of the extra amount (including the seven and a half Kav; see Rashbam to 103b, DH Yeser Mikan). This is also the opinion of the RA'AVAD.
(b) The Rashbam cites another opinion which explains that when Rav Nachman says, "If there is more than nine Kav it goes back," he means more than nine Kav over the normal amount of one quarter Kav per Se'ah, regardless of how many Kor are being sold.
(c) The Rashbam cites a third opinion which explains that if there is more than nine Kav per Kor, all of the land goes back to the seller. (Y. MONTROSE)