QUESTION: The Gemara teaches that according to Rebbi Yehudah, "Tzad Echad b'Ribis" is permitted. "Tzad Echad b'Ribis" refers to a transaction which can have two possible outcomes, one of which involves Ribis. He maintains that a transaction that involves Ribis is prohibited only when Ribis definitely will be involved, but not when the presence of Ribis depends on the outcome of the transaction. The classic case of "Tzad Echad b'Ribis" is where a borrower gives his field to the lender and stipulates that if he does not repay the loan, the lender will acquire the field (for the money of the loan) retroactively. In the interim, the lender eats the produce of the field. According to the Tana Kama in the Beraisa, this is forbidden as Ribis, because if the borrower pays back the loan on time and repossesses his field, the sale will be invalidated and all the fruit that the lender ate will have constituted Ribis. Rebbi Yehudah says that this is permitted because there exists the possibility that the borrower will default on the loan, making the sale valid and entitling the new owner to eat from the fruit of the field. As long as this possibility exists, there is no prohibition against entering such a transaction.

TOSFOS (DH Tzad Echad) questions Rebbi Yehudah's opinion from the case of "Se'ah b'Se'ah." The Mishnah later (75a) prohibits a person from borrowing a Se'ah of flour with a commitment to return a Se'ah a flower, because the market price of flour may rise, in which case the borrower will end up returning something (a Se'ah of flour) of greater value than what he borrowed. According to Rebbi Yehudah, why is that case not considered "Tzad Echad b'Ribis" and permitted? Since there is a possibility that the price will not rise, why is the case of "Se'ah b'Se'ah" forbidden according to Rebbi Yehudah?

(a) TOSFOS explains that there is a fundamental difference between the two cases. "Tzad Echad b'Ribis" occurs only when it is within the control of the borrower to pay or not to pay Ribis. In the case of "Se'ah b'Se'ah," the borrower has no control over the market price of wheat. Since it is not within his control, he is not allowed to borrow a Se'ah of wheat with intent to pay back a Se'ah of wheat.

The NESIVOS SHALOM clarifies the intent of Tosfos. One of the primary factors involved in determining whether or not a transaction involves Ribis is "Ketzitzah" -- "setting an amount." In a case of "Tzad Echad b'Ribis," even after the terms have been set, no stipulation has been made that the borrower will pay Ribis. Since there is no "Ketzitzah," the transaction is permitted. In contrast, in the case of "Se'ah b'Se'ah," the terms of the loan included the stipulation that a Se'ah of wheat be paid back regardless of the market price of wheat. This stipulation constitutes a certain degree of "Ketzitzah," and thus the transaction is forbidden.

The AYELES HA'SHACHAR asks that this explanation seems to contradict the concept of "Ribis Me'ucheres" -- the law that forbids a borrower from giving extra money (or objects) to the lender even after he has already paid back the loan. According to Rebbi Yehudah, why should this be forbidden? If "Tzad Echad b'Ribis" is permitted, even though the borrower originally knew that he might have to pay Ribis, why should the borrower not have the option of paying Ribis later, after the loan has been repaid? The Ayeles ha'Shachar answers that the difference is based on how the decision to pay Ribis is established. When a borrower pays "Ribis Me'ucheres," he clearly decided to pay Ribis. In contrast, when a borrower makes a condition which allows for the possibility that he will end up having to pay Ribis, he is not making a clear stipulation of Ribis. If he ends up having to pay, he pays only as a result of a condition that was not directly linked to Ribis.

(b) TOSFOS in Megilah (27b, DH v'Rebbi) answers that the leniency of "Tzad Echad b'Ribis" is based on the fact that it involves a sale, as opposed to a loan. This is also implied by RASHI here (DH Rebbi Yehudah), the RA'AVAD, and others. (Y. Montrose)

OPINIONS: The Gemara discusses a case in which a person receives money from someone else and finds that the person gave him more money than they agreed upon. Is he allowed to attribute the extra money to the other person's generosity and assume that it is a gift, or must he point out the over payment to the other person? Rav Nachman says that if the extra money is an amount that might reasonably be the result of a mistake in calculation, he must mention the overpayment to the other person. If the amount is unlikely to be a result of a miscalculation, he may attribute it to the other person's generosity.

Rav Acha says that it is reasonable to assume that a mistaken calculation was made when the overpayment is a denomination of ten or five. (It was the custom to count large quantities by counting from one to ten (or to five), and then again from one to ten (or to five), and remembering how many sets of ten (or five) one has already counted. Hence, it was possible to err in the number of tens (or fives).)

The Gemara's ruling seems problematic. The recipient of the extra money should simply ask the payer whether or not he intended to give him a gift! The Rishonim explain that the recipient indeed is required to ask the payer about the overpayment whenever possible. However, in a case where it is not possible, such as when the payer died, he is not required to inform the payer's heirs about the overpayment if it was not likely the result of a miscalculation.

Does Rav Nachman's ruling apply to any recipient of money, even a lender who receives money from a borrower? If the lender is permitted to keep the overpayment in such a case, why is it not considered Ribis?

(a) RASHI (DH Iy bi'Chedei) apparently understands that Rav Nachman's ruling applies only to a lender who gives extra money to a borrower. A lender cannot accept extra money from a borrower who is paying him back, since that indeed would constitute "Ribis Me'ucheres." RAV YOSEF SHALOM ELYASHIV shlit'a (quoted in He'oros b'Maseches Bava Metzia) explains that although Rashi generally maintains that "Ribis Me'ucheres" is permitted when the borrower does not specify that he is paying extra money due to the loan, Rashi agrees that when the borrower gives the extra money at the time he pays back the loan, it is prohibited.

(b) The RAMBAM (Hilchos Malveh v'Loveh 4:10) explains that Rav Nachman's ruling applies even when a borrower pays back his loan to the lender. Why is the extra money that he pays not considered "Ribis Me'ucheres"? In fact, the Rambam himself rules (unlike Rashi) that even when the borrower does not specify that he is giving the extra money because of the loan, it is prohibited because of "Ribis Me'ucheres." Why, then, does the Rambam rule that a lender may keep the extra money given to him by the borrower?

Rav Elyashiv explains that the case must be one in which the borrower is friendly with the lender, and he sometimes gives gifts out of friendship even when he has not borrowed money from him. In such a case, the lender is permitted to keep the extra money. (Y. Montrose)