The Beraisa discusses a case where Reuven counters Shimon's claim that he stole his field with a Sh'tar and a Chazakah. According to Rebbi, we contend only with the Sh'tar. Rabban Shimon ben Gamliel says - 'be'Chazakah'.

We reject the text in Rabban Shimon ben Gamliel 'Af be'Chazakah' - because it is subject to a Machlokes Amora'im later in the Sugya. Clearly then, it is not explicit in his words (see also Tosfos DH 'be'Chazakah).

According to Rav Dimi, their Machlokes is based on the principle 'Osiyos Niknos bi'Mesirah' - Rebbi holds 'Osiyos Niknos bi'Mesirah'. Consequently, if the claimant does not produce the Sh'tar, we suspect that he may have returned it, in which case the field will have reverted to the original owner, and the Chazakah will be worthless. Whereas according to Rabban Shimon ben Gamliel, who holds 'Ein Osiyos Niknos bi'Mesirah', there is no reason not to go by the Chazakah.

According to Rabban Shimon ben Gamliel, the reason that one can acquire a field with a Sh'tar is - because the initial transaction is recorded in the Sh'tar, and has nothing to do with the above Machlokes, where it is not.

When Abaye asked Rav Dimi whether his interpretation did not clash with Rabah, in whose opinion Rabban Shimon ben Gamliel holds 'Osiyos Niknos bi'Mesirah' - he replied that it did (and so what!)

Abaye did not accept Rav Dimi's answer however - because according to Rav Dimi, Rabah's Kashya on the previous Beraisa (why Rabban Shimon ben Gamliel's opinion does not extend to where the Sh'tar was stole or lost) remains unanswered.

So Abaye establishes the Machlokes where one of the witnesses turns out to be a relative or Pasul - and they argue over the Machlokes between Rebbi Elazar who holds that 'Eidei Mesirah Karsi' (Rebbi, who therefore validates a Sh'tar without witnesses or, we initially think, with Pasul witnesses), and Rebbi Meir, who does not (Rabban Shimon ben Gamliel, who therefore requires the proof of a Chazakah).

With regard to 'Osiyos' however, both Tana'im hold - 'Osiyos Niknos bi'Mesirah'

We reject Abaye's explanation however, on the basis of a statement by Rebbi Elazar (the Tana) himself - who states that a Sh'tar that is 'intrinsically a forgery' is Pasul (and that he and Rebbi Meir are arguing over a Sh'tar which does not contain witnesses at all).

Rebbi Avina (alias Ravina) therefore establishes the Machlokes, so that they still argue the same Machlokes as Rebbi Elazar and Rebbi Meir - where the Sh'tar had no witnesses at all (the exact case over which Rebbi Meir and Rebbi Elazar are arguing). Here as well, Rebbi holds like Rebbi Elazar, and Rabban Shimon ben Gamliel, like Rebbi Meir.

Alternatively, they are arguing over a Sh'tar which the 'seller' admits to having written, and the basis of their Machlokes is - whether the 'purchaser' subsequently needs to corroborate the Sh'tar (Rabban Shimon ben Gamliel) or not (Rebbi).

The reason that Rabban Shimon ben Gamliel does not apply the principle 'ha'Peh she'Asar Hu ha'Peh she'Hitir' (and believe the 'seller' that although he wrote the Sh'tar, the transaction did not really take place) is - because, even if the 'seller' were to deny having written the Sh'tar, we would not suspect the 'purchaser' of having forged it (in which case it is not really a 'Peh she'Asar').

Rebbi holds in a Beraisa, that if a creditor and a debtor are holding the Sh'tar Halva'ah, which the creditor claims he lost before the debtor paid, and the debtor claims that he lost it after having paid, 'Yiskayem ha'Sh'tar be'Chosamav', which means that - the claimant needs to verify his claim, before he receives anything.

Rabban Shimon ben Gamliel rules ' - that he receives a half anyway.

We query Rebbi from the Mishnah 'Shenayim Ochzin be'Talis ... where the Tana rules 'Yachloku' - raising the question why he does not rule 'Yochloku' here too.

Rava Amar Rav Nachman therefore explains that, had the Sh'tar been verified, even Rebbi would agree that the creditor would claim half the debt - and that they argue in a case where it was not verified, and Rebbi's reason is based on the principle 'Modeh bi'Sh'tar she'Kasvo, Tzarich le'Kaymo'.

The problem from the earlier Beraisa ('ha'Ba Lidun bi'Sh'tar u've'Chazakah') is that - Rebbi and Rabban Shimon ben Gamliel appear to have switched opinions?

We resolve the discrepancy by indeed switching their opinions in the first Beraisa to conform to the second one.

Alternatively, we establish the Machlokes in the latter Beraisa 'bi'Le'varer ka'Miflegi' - whether a litigant is obligated to substantiate every argument that he presents, even one that is unnecessary.

And we support this with a case of Rav Yitzchak bar Yosef who lent Rebbi Aba money. When the latter claimed to have paid in front of P'loni u'Peloni u'Peloni - Rebbi Yitzchak Nafcha insisted that he bring all three witnesses to corroborate his claim.

The defendant queried this however, from the established ruling - 'ha'Malveh es Chavero be'Eidim, Ein Tzarich le'Par'o be'Eidim' (in which case, it appeared unnecessary for him to have to corroborate his claim).

In reply, Rebbi Yitzchak Nafcha quoted Rebbi Aba (Amar Rav Ada bar Ahavah Amar Rav) himself, who ruled, in a case where the debtor claims that he paid in the presence of P'loni u'Peloni u'Peloni - that he had to bring them to Beis-Din ...

... like the opinion of Rebbi.

Rebbi Aba nevertheless objected to Rebbi Yitzchak Nafcha's ruling from a statement by Rav Gidal Amar Rav - who ruled like Rabban Shimon ben Gamliel ('be'Chazakah [ve'Lo bi'Sh'tar']).

Rebbi Yitzchak Nafcha replied that - he followed the opinion of Rebbi, and that Rebbi Aba (who personally held like Rabban Shimon ben Gamliel [see Maharsha]) therefore remained obligated to bring the witnesses (see also Rabeinu Gershom).

Ultimately however - we rule like Rabban Shimon ben Gamliel (despite the principle 'Halachah ke'Rebbi me'Chavero'), that 'Ein Tzarich Le'varer', like Rav Gidal Amar Rav).

Our Mishnah discusses someone who paid part of his debt. The problem is that - if the Sh'tar is torn up, the creditor will lose the balance, whereas if it is not, he is likely to claim again.

Rebbi Yehudah holds 'Yachlif' - which means that - they write a fresh Sh'tar (though the details will only become clear in the Beraisa that we will quote shortly).

Rebbi Yossi - holds 'Kosvin Shover' (one writes a receipt).

In countering Rebbi Yehudah's argument (that it would not be fair to expect the debtor to look after a receipt, to prevent it from being eaten by mice), Rebbi Yossi argues that - it is preferable for the debtor to have to look after his receipt than for the creditor to lose his leverage over the debtor (by forcing him to pay the rest of his debt quickly before he loses it).

The basis of Rebbi Yossi's opinion is - the principle 'Eved Loveh le'Ish Malveh' (a borrower is indebted to the creditor and is therefore subservient to him).

Rav disagrees with both Rebbi Yehudah and Rebbi Yossi. Even though an Amora does not have the right to argue with Tana'im - Rav is unique among Amora'im, inasmuch as he bears the title 'Tana'.

He ryules that Beis-Din tear the Sh'tar and write a fresh Sh'tar with the original date.

After quoting the Beraisa 'Eidim Mekar'in es ha'Sh'tar ve'Kosvin lo Sh'tar Acher mi'Z'man Rishon' (though this is not the actual wording of the Beraisa as we shall see shortly), Rav Nachman (or Rebbi Yirmiyah bar Aba) commented to Rav Huna that - had Rav seen this Beraisa, he would have admitted that the Halachah is like Rebbi Yehudah, seeing as (considering that there is no difference whether it is the witnesses who write the new Sh'tar or Beis-Din) his ruling actually concurs with that of Rebbi Yehudah.

Rav Huna replied that - Rav was indeed conversant with the Beraisa, yet he did not retract from his statement, because in spite of Rav Nachman, there is a major difference between Beis-Din (who are merely exercising their rights of 'Hefker Beis-Din Hefker', by writing a second Sh'tar backdated to the original date) and the witnesses (whose Sh'lichus ended when they wrote the initial Sh'tar and signed on it, and who have no mandate to write a second one).

When Rav Yehudah Amar Rav said 'Eidim she'Kosvin Afilu Asarah Sh'taros al Sadeh Achas', he meant that - if a Sh'tar is lost, they have to write another one (even if this happens ten times).

To answer the apparent contradiction in Rav, Rav Yosef establishes Rav's latter ruling by a Sh'tar Matanah - which does not incorporate Acharayus, and seeing as the problem of the witnesses' writing a second Sh'tar is due solely to the Shibud that it creates, there is no longer anything to be afraid of.

Rabah establishes Rav's latter ruling - in the case of a Sh'tar (even a Sh'tar Mecher) that does not contain Acharayus.