The Gemara on today’s daf presents two similar cases, but offers two different rulings in them.
In the first case, one person said to another “what do you want with my field?” The second one answered “I purchased it from you, and here is the bill of sale.” The first replied “that bill of sale is a forgery!” The second leaned over to Rabba who was presiding over the court and said “It really is a forgery, but the real contract was lost, so I thought that I would produce this one in order to bolster my claim.”
Rabba announced that he accepted the second man’s argument, since he has no reason to lie – had he wanted to lie, he could have insisted that the contract was a good one. Rav Yosef objected to this ruling, saying that the contract was clearly worthless, so the man had no claim.
In the second case, one person said to another “pay me the hundred zuz that you owe me, and here is the promissory note proving that you borrowed from me!” The second one answered “that note is a forgery!” The first one leaned over to Rava who was presiding over the court and said “It really is a forgery, but the real contract was lost, so I thought that I would produce this one in order to bolster my claim.”
Rabba announced that he accepted the first man’s argument, since he has no reason to lie – had he wanted to lie, he could have insisted that the contract was a good one. Rav Yosef objected to this ruling, saying that the contract was clearly worthless, so the man had no claim.
Somewhat surprisingly, Rav Idi bar Avin rules like Rabba in the first case and like Rav Yosef in the second. In each case we leave the valuables in question in the hands of the person who is holding them – the field in the hands of the person living or working the land; the money in the hands of the person who was holding it.
The Rashbam suggests that Rav Idi is not really offering a significant ruling, rather he was unsure of what the proper ruling is, and therefore leaves things as they were.