Question: First the Gemara asks for Rebbi Yehudah's reason, suggesting that Rebbi Shimon's without the Gezeirah Shavah is more logical; then it asks for Rebbi Shimon's reason, which suggests that Rebbi Yehudah's reason is more logical?

Answer #1: We find a similar sequence in Bava Kama (Daf 10a), in connection with 'Ten men who beat a man with ten sticks (and killed him)', where one opinion interprets the Pasuk "ve'Ish ki Yakeh Kol Nefesh Adam" to mean - until he kills the victim's Nefesh on his own, which the other opinion explains even a bit of a Nefesh.

Answer #2: According to Tosfos' explanation earlier (on the previous Amud , DH 'Mah Lehalan') there is no problem ...

Answer #2 (cont.): Since the Pasuk implies that the field goes out to the Kohanim - only one opinion requires the Gezeirah Shavah to teach us that he has to pay, the other, that it goes out free of charge.

Question: The simple P'shat in the Pasuk is like Rebbi Eliezer - "If he fails to redeem the field" - the owner; "and if he sells ... " - the treasurer sells it to a third party; "Then when goes out in the Yovel it shall belong to the Kohanim" ...

Question (cont.): A proof that it does not go to the Kohanim unless it has been sold to someone else, and that if no one else redeemed it and it is still in the hands of the treasurer, it does not go to the Kohanim ...

Question (concl.): So we see that the simple P'shat in the Pasuk goes like Rebbi Eliezer?

Answer: According to Tosfos' explanation earlier (Ibid.) that "ve'Im Lo Yigal" and "Im Machar" are speaking in two different cases, the problem falls away, because it implies that either way it goes to he Kohanim.

Question: Why does the Gemara not ask - If it is referring to the first Yovel, the Torah writes "v"e'Im Ga'ol Yig'al es ha'Sadeh ... ve'Kam lo" (See Avodah Berurah)?

Answer: Perhaps that is what the Gemara means to ask?

Question: It is possible to establish it by the first Yovel - where somebody else redeemed it from the treasurer and the owner from him ...

Reason: Because then it has the Din of an acquired field, which goes to the Kohanim in the Yovel? ...

Source: As we learned in the Mishnah (above, Daf 25a) ''If somebody else or a relative redeems it and he redeems it (from him) it goes out from his domain in the Yovel.

Answer: It is not logical to say that the Pasuk is referring to a redemption that takes place from a third person to the hands of the owner, since it is speaking specifically about a redemption directly from the treasurer ...

Reason: Since, should a third person redeem it, he will not sell it to the owner if he does not want to ...

Answer (cont.): That is why "Lo Yiga'el Od" is speaking exclusively about a field that is redeemed from theb treasurer.

Clarification: According to Rebbi Eliezer - is he like somebody else or not? ...

Reason for Side #1: Because, seeing as he did not redeem it and it is still in the hands of the treasurer, the owner may redeem it ...

Implied Question: Because when the Torah writes "Lo Yiga'el Od", from which we extrapolate that it canot be redeemed to its former status ...

Answer: That speaks exclusively where someone else re4deemed it from the treasurer ...

Conclusion: But if nobody did, and the field was never distributed among the Kohanim, about such a scenario, the Pasuk "Lo Yiga'el Od" is not speaking ...

Conclusion (cont.): And the Din there is that it remains in the possession of the owner who ultimately redeemed it from the treasurer.

Clarification: This refers to a Sadeh Achuzah which the owner declared Hekdesh and someone else redeemed before the Yovel, which goes out to the Kohanim in the Yovel ...

Clarificarion (cont.): The Kohen who received it is then Makdish it - in the second Yovel - and the owner comes and redeems it (from him) ...

The Havah Amina: We would have thought, had the Torah not written "Im Lo Yiga'el" - that it can no longer be redeemed, even like a purchased field ...

The Conclusion: Therefore the Torah adds that it cannot be redeemed to its former status (like a Sadeh Achuzah), but it can be redeemed to be like a Sadeh Mikneh ...

The Conclusion (cont.): And it reverts to the Kohanim in the Yovel.

Explanation: And it now transpires that "ve'Hayah ha'Sadeh be'Tzeiso ba'Yovel ... " refers to both cases of which the Torah speaks, both to "Im Lo Yig'al ha'Sadeh" and to "ve'Im Machar le'Ish Acher" ...

Explanation (cont.): Because the Pasuk is speaking about two cases, as Tosfos explained earlier (Daf 25b DH 'Mah'), in which case, that is also how we will explain according to Rebbi Eliezer (See Avodah Berurah DH 'u'Le'el Miba'i leih')

Explanation of Sugya on Amud Alef: Earlier (on Amud Alef) the Gemara searching for Rebbi Eliezer's reason, continued 'What is indeed his reason? and concluded ...

Explanation of Sugya on Amud Alef (cont.): Quoting Rava 'The Pasuk says "And the field shall be when it goes out in the Yovel" , 'when it goes out from the domain of somebody else' - since 'when it goes out' implies that it goes out from the hand of the treasurer ...

Explanation of Sugya on Amud Alef (concl.): But as long as it is in the hands of the treasurer it does not go out in the Yovel.

Reason: Because 'A person cannot be Makdish something that does not belong to him.

Explanation #1: At first glance it seems that it speaks where a third person redeemed the field from the treasurer before the Yovel.

Explanation #2: Rashi however, in his explanation of the Chumash, establishes it even where a third person did not redeem it, but it is still in the hands of the treasurer ...

Explanation #2: It nevertheless goes out in the Yovel to the original owner "to whom the portion of land initially belonged".

Reference: Tosfos explained this in 'ha'Shole'ach' (Gitin, Daf 48a [See also Tosfos Bava Basra, Daf 50b DH 'Kinyan'])