A Mistake in Measurement, Weight, or Amount - Rav Ofer Livnat

Publicized in the weekly leaflet Hemdat Yamim - Eretz Hemdah

 
This week in the Daf Hayomi the Gemara (90a) states that in a case where the buyer and the seller agreed upon a purchase of a certain measurement, weight, or amount of merchandise, and the merchandise supplied was lacking or in excess even a small amount, we do not consider the difference to be forgiven. This is in distinction to the case where the price agreed upon was different from the real price of the merchandise, in which case the Halacha is that a difference of less than a sixth is considered to be forgiven. However, for a difference of measurement, weight, or amount, even a small difference is not considered to be forgiven.

The question is, what happens when such a difference is discovered? The Rashbam (d"h kol davar shebemidah) claims that the sale is void. The Rashbam learns this from a case of a price difference greater than a sixth. Just like when the difference between the price agreed upon and the real price is greater than a sixth, the Halacha states that the sale is void, so too when there is even a small difference in measurement, weight, or amount, the sale is void.

The R"I Migash (d"h kol) disagrees with the Rashbam. He claims that the sale is not void but rather the difference must be given or returned. If the merchandise is lacking then the seller must supply the amount lacking. If there is extra, the buyer must return the excess to the seller. For example, if they agreed upon 100 walnuts for a certain price, and there ended up being only 99 walnuts, the seller must supply another walnut. If there were 101 walnuts then the buyer must return 1 walnut to the seller.
The R"I Migash explains that this case is not similar to that of a price difference. Regarding a price difference, the problem is with the deal agreed upon, since the price agreed upon was not a fair one. However, in our case, the deal itself was fair, and the problem is only in the execution of the deal; as a mistake was made in the supply of the merchandise. Therefore, the sale stands and the mistake must be corrected. The Rambam (Mechira 15, 1-2), Ramban (Baba Batra 103b d"h matnitin), and Rashba (Kidushin 42b umistabra) all agree with the R"I Migash.

However, if we follow the opinion of the R"I Migash, there still remains another question. What happens if the difference cannot be completed? For example, if the merchandise was lacking, and the seller cannot supply the missing amount, then what do we do? The Ramban and the Rashba dispute this question. According to the Ramban, if the missing amount cannot be completed, the sale is void. However, the Rashba claims that even in such a case the sale is not void, and one must pay the value of the missing merchandise.

:Summary and Ruling

The Shulchan Aruch (232, 1) rules like the opinion of the R"I Migash that in a case where a mistake occurred in the measurement, weight, or amount of the supplied merchandise the sale stands and the difference must be completed. In a case where the difference cannot be completed, the Sma (ibid, 2) rules like the opinion of the Ramban that the sale is void.

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