cellio | daf bit: Bava Batra 137

Today the talmud discusses conditional gifts -- specifically, gifts that must be returned. This is not the same thing as a loan, where ownership never transfers (only control). The first case it discusses involves an etrog, an item that is used for ritual purposes during Sukkot. The person using the etrog for the ritual must own it, so that's a case where a loan would not suffice but a conditional gift does. With that as background...

Raba said: if one said to another, "I give this etrog to you on condition that you return it to me", and the recipient uses it for the ritual purpose and then returns it, then the recipient has fulfilled his obligation for the ritual. However, if he used it for the ritual purpose and did not return it, then he has not fulfilled the ritual obligation. (The g'mara does not here say that he is using a stolen item for a mitzvah, which is not valid, but it seems to be implied.) From this statement of Raba's we learn that a gift given on the condition that it be returned is a proper gift -- for that interval the recipient is the owner.

Raba said further, in the name of R' Nachman: if one says: "I give this ox to you on condition that you return it to me" and the recipient consecrates the ox (so that it can no longer be used for other purposes) before returning it, both the consecration and the return are valid. That's R' Nachman. But, Raba asked him, what has he returned to him? He can't use the ox any more! R' Nachman replied: but what has he taken away from him? He received an ox and returned an ox, bodily intact! R' Ashi then said it depends on exactly what the first person said. If he said "on condition that you return it", then he has no claim -- the other did in fact return it. If, however, he said "on condition that you return it to me", he can demand compensation because "to me" implies that he'll be able to use it. (137b)