Q: I lent a neighbor a bag full of quarters, but he lost it before counting the exact amount it contained. How much does he have to pay?

A: If both parties admit to the loan, but neither knows or remembers the sum, the borrower must pay the amount that he is certain about. Some say that there remains a moral obligation to compromise with the lender about the remaining sum, whereas most maintain that there is not even a moral obligation to do so (C.M. 75:18; Shach 75:58).

On the other hand, if the lender claims a definite amount and the borrower does not remember exactly how much, he is obligated to pay the full amount that the lender claims, within reason. This is because the borrower admits partially and is therefore obligated in a severe Torah oath, which he is unable to take. This principle is known as: mitoch she’aino yachol lishava meshalem – since he is unable to swear, he must pay (75:19).

The primary exception to this rule of mitoch is when the borrower is willing and able to pay immediately the amount he acknowledges (heilech). In this case, he needs to pay only that amount and is exempt from the remainder (87:1).