Beit Kor, the seventh perek of Massekhet Bava Batra, begins on today’s daf. Its focus is on the purchase of different types of real estate, and in particular on how deficiencies or blemishes will affect the sale. Just as the previous perek dealt with deficiencies in moveable objects, similarly in real estate there are some deficiencies that are accepted as part of a field and others that no purchaser would knowingly accept. Since it is natural for fields to include hills and valleys, rocks and broken areas, it is necessary for the Talmud to establish what is a natural and acceptable blemish, and when the loss to the buyer is significant enough for him to demand a reduction in price, or a replacement for the area that cannot be used.
The first Mishna teaches that if a person agrees to sell beit kor afar – land upon which a kor of grain can be grown – if there are crevices in the ground that are ten tefaḥim deep, or rocks that are ten tefaḥim high, those areas are not to be included in the sale. If, however, the agreement was that ke-beit kor – approximately a beit kor – was being sold, then such crevices or rocks would be included.
A beit kor is a measure of volume; it is the size of a field that will grow 30 se’a of grain (248 or 430 liters, depending on the definition of a se’a), which is 75,000 square amot (17, 280 or 24,900 square meters). The Nimmukei Yosef points out that the agreement cannot possibly be one where they agree on a specific field or portion of a field, since in that case the agreement would take effect. The case of the Mishna must be when the seller presents a larger field and they agree that an unspecified area of a beit kor was to be sold.