Bava Metzia page 35b.

A hirer of an animal loans out the animal to a borrower and it dies, (Bava Metzia page 35b). The sages say the hirer takes an oath that it was not his fault, and the borrower pays the hirer. R Jose disagrees, and asks how can the hirer make business with someone else's animal? There are two ways of understanding this. Tosphot on the page says the argument is the same one as brought later in the Gemara. [Rav Adi bar Abin asked on the sages, "Why not just have the hirer tell the renter, 'Let us delete your oath, and I will deal with the borrower directly.'" Abye answered him the oath is not what causes the transfer but the death of the animal.] When does the transfer of responsibility happen, at the time of the oath or of the moment the animal died? (The Ran (on the Rif) and other Rishonim disagree.) Rav Shach brings the idea of Reb Aaron Kotler that a claim of an unforeseen accident is not a valid claim, but also shows how it can be considered a valid claim and that both R Yose, and the sages might agree with this. To rav shach this is the argument between R Yose and the sages. Thus, To the sages, we start off with the assumption that the claim of and unforeseen accident is valid. We just require an oath to make doubly sure. That is that the transfer of monetary responsibility happened when the animal died. To R jose the claim in itself is not considered valid. Thus, the owner can tell the hirer to not take an oath and he will collect from the borrower directly. ------------------------------------------------A שוכר of an animal loans out the animal to a שואל and it dies, (בבא מציעא ל''ה ע''ב). The חכמים say the שוכר takes an oath that it was not his fault, and the borrower pays the שוכר. HOWEVERר’ יוסי , disagrees, and asks "How can the שוכר make business with someone else's animal?" There are two ways of understanding this. תוספות on the דף says the argument is the same one as brought later in the גמרא. When does the transfer of responsibility happen, at the time of the oath or of the moment the animal died? (The ר''ן (on the רי''ף) and other ראשונים disagree.) רב שך brings the idea of ר' אהרן קוטלר that a claim of an unforeseen accident אונסים גדולים is not a valid claim, but also shows how it can be considered a valid claim and that both ר' יוסי, and the חכמים might agree with this. To me it seems best to say that that in itself is the exact argument between ר' יוסי and the חכמים. Thus, To the חכמים, we start off with the assumption that the claim of and unforeseen accident (אונסים גדולים)is valid. We just require an oath to make doubly sure. That is that the transfer of monetary responsibility happened when the animal died. To ר’ יוסי the claim in itself is not considered valid. Thus, the owner can tell the שוכר to not take an oath, and he will collect from the borrower directly. [The background here is that a hirerשוכר takes an oath in a case of unforeseen accidents אונסים גדולים but a borrower שואלalways pays no matter what the circumstances were.] I think to mention here that it is curious that R. Jose does not mention an oath, so it might be difficult to say the reasoning of Rav Adi bar Abin is the reasoning of R. Jose might be difficult. Also, I wanted to mention what Abaye meant by saying the death of the animal is what causes the transfer of responsibility. That is the difference between a loan and borrowing an animal. If the money of the loan is lost it makes no difference. The same responsibility to pay it back remains the same. but with borrowing an animal the death of the animal causes a new set of laws to be applied. Before it died the borrower had to give it back to the lender. But after it died, the familiar set of laws apply. A free guard swears for theft and loss. A paid guard pays for theft and loss, but swears when it is a case of large accidents like being accosted by armed robbers. A renter is the same. A borrower pays for everything.----------------------I think to mention here that it is curious that ר' יוסי does not mention an oath, so it might be difficult to say the reasoning of רב אידי בר אבין is the reasoning of ר' יוסי might be difficult. Also, I wanted to mention what אביי meant by saying the death of the animal is what causes the transfer of responsibility. That is the difference between a loan and borrowing an animal. If the money of the loan is lost it makes no difference. The same responsibility to pay it back remains the same. but with borrowing an animal the death of the animal causes a new set of laws to be applied. Before it died, the borrower had to give it back to the lender. But after it died, the familiar set of laws apply. A free guard swears for theft and loss. A paid guard pays for theft and loss, but swears when it is a case of large accidents like being accosted by armed robbers. A renter is the same. A borrower pays for everything.--------------------- \\\a further note concerning the discussion between Abaye and Adi bar Abin., (Rav Adi bar Abin asked on the sages, "Why not just have the hirer tell the renter, 'Let us delete your oath, and I will deal with the borrower directly.'" Abaye answered him the oath is not what causes the acquisition, but the death of the animal.) The question is on the surface, neither an oath nor the death of the animal confers acquisition. I answered this partly saying the argument between R. Jose and the sages is the same argument between Abaye and Rav Adi; and that argument is the same as the argument between Rav Shach and Reb Aaron Kotler. This explains Rav Adi well, however it still leaves me wondering what Abaye meant. I would like to answer this question now. I think Abaye meant to say that it is not the oath which causes acquisition to the renter. How do we know this? Because if there would be two witnesses that the animal died by itself with no negligence on the part of the borrower or renter, then the renter would not be required to pay anything to the owner of the animal. Therefore, his acquisition of the value of the animal does not depend on the oath but on the fact that we know the animal dies because of an unavoidable accident.----------------------a further note concerning the discussion between אביי andרב אידי בר אבין . THE CASE WAS רב אידי בר אבין asked on the sages, "Why not just have the hirer tell the שוכר, 'Let us delete your oath, and I will deal with the שואל directly.'" אביי answered him the oath is not what causes the acquisition, but the death of the animal. The question is ]on the surface[, neither an oath nor the death of the animal confers acquisition. Tosphot answered this partly saying the argument between ר' יוסי and the sages is the same argument between אביי and רב אידי; and that argument is the same as the question is if a claom of unavoidable accident is considered valid even before an oath is taken. that is- what do we think happened even before claims came. This explains רב אידי well, however it still leaves me wondering what אביי meant. I would like to answer this question now. I think אביי meant to say that it is not the oath which causes acquisition to the שוכר. How do we know this? Because if there would be two witnesses that the animal died by itself with no negligence[פשיעה] on the part of the שואל or שוכר, then the שוכר would not be required to pay anything to the owner of the animal. Therefore, his acquisition of the value of the animal does not depend on the oath, but on the fact that we know the animal dies because of an unavoidable accident אונס גדול .