Neighbors frequently borrow small amounts of food from each other, such as a dozen eggs or a cup of flour. Similarly, classmates borrow cans of soda or danishes from each other.
A class decides to make a late night siyum, and asks the fellow who runs the soda machine if they can borrow twenty cans of soda, which they subsequently repay.
Do any of these cases involve a ribbis issue?
Introduction: Although mid’oraisa there is no issue, nevertheless Chazal instituted a gezeirah that one should not borrow (even) a fixed measure of food or merchandise and repay with a similar measure. Although they are repaying the same amount; nevertheless, since the market price of merchandise is subject to fluctuation and may increase in the interim, there is a possibility that the item returned will now be more valuable. This is known as seah beseah.
This only applies when returning a different item, such as borrowing a dozen eggs and repaying with a different dozen eggs. Borrowing a car or an MP3 player, where one returns the same item borrowed, would not be subject to this prohibition, even if there was a price increase in the interim.
There are two primary exceptions to the gezeirah of seah beseah mentioned in the Gemara:
Yatza ha’shaar: When the item borrowed has a fixed market value.
Yesh lo: The borrower has some of that item in his possession at the time of the loan (even if the lender gave him this small amount as a present at the time of the loan).
to be continued…