Daf Yomi Ketubot 64b-65b: Establishing Like Rav Nachman In Dinim

When translating Rif Yomi, I encountered the following gemara:

{Ketubot 64b}
Mishna:

נותן לה מעה כסף לצרכיה ואוכלת עמו מלילי שבת ללילי שבת
ואם אינו נותן לה מעה כסף לצרכיה מעשה ידיה שלה
ומה היא עושה לו משקל חמש סלעים שתי ביהודה שהן עשר בגליל או משקל עשר סלעים ערב ביהודה שהן עשרים בגליל
ואם היתה מניקה פוחתין לה ממעשה ידיה ומוסיפין לה על מזונותיה
בד"א בעני שבישראל אבל במכובד הכל לפי כבודו

He gives her a ma'ah of silver for her needs, and she eats with him from one night of Shabbat to the next night of Shabbat.
And if he does not give her a ma'ah of silver for her needs, her handiwork is hers.
And what does she do for him? The weight of 5 sela of warp in Judea, which are 10 in Galilee {based on different standards of measurement}, or the weight of 10 sela woof in Judea, which are 20 in Galilee.
And if she is nursing, they reduce from her {required} handiwork and add to her food.
Where are these words said? By the poorest man in Israel. But by the honored, all according to his honor.

{Ketubot 65b}

Gemara:

מאי אוכלת
רב נחמן אמר אוכלת ממש
ושמואל אמר תשמיש כדכתיב אכלה ומחתה פיה
וקי"ל כרב נחמן בדיני

What is meant by the statement that "she eats?"
Rav Nachman said: She actually eats.
And Shmuel said: Intercourse, as is written {Mishlei 30:20}

כ כֵּן, דֶּרֶךְ אִשָּׁה-- מְנָאָפֶת: אָכְלָה, וּמָחֲתָה פִיהָ; וְאָמְרָה, לֹא-פָעַלְתִּי אָוֶן.

20 So is the way of an adulterous woman; {N} she eateth, and wipeth her mouth, and saith: 'I have done no wickedness.' {P}

And we establish like Rav Nachman in dinim.

This is an interesting reason to rule like Rav Nachman. After all, we have another rule, that while we rule like Rav in issurim, we rule like Shmuel in dinim. As such, both Rav Nachman and Shmuel have this general rule that we rule like them in dinim. Why establish like Rav Nachman?

In fact, as the Korban Nesanel points out (on the Rosh) there is a dispute between Rif and Rosh on this matter. While Rif holds that this principle about Rav Nachman applies in all cases, even in dispute between Rav Nachman and Shmuel, Rosh disagrees and maintains that in such a case, Shmuel wins out.

In masechet Bava Metzia, perek Hazahav, siman 21, Rosh explains this:

1. While there is a principle that the halacha is like Rav Nachman in dinim, this is only against Rav Sheshet. (Just as we state the principle by Shmuel as against Rav.) As the saying goes, "the halacha is like Rav Nachman with regard to dinim and like Rav Sheshet in prohibitions."
2. You might say that Rav Nachman was later, and the hilcheta kibatrai, the halacha is like the latter one. However, Rosh claims that this principle only applies to the Amoraic generations of Abaye and Rava and on. Shmuel and Rav Nachman are earlier generations. Therefore, the principle to be applied would be ruling like the Rebbe over the Talmid.

Thus, we would expect that Rosh would rule locally in this case that the halacha is like Shmuel. Instead, he says just like the Rif that the halacha is like Rav Nachman by dinim. Korban Netanel points out how some read this as a reversal by the Rosh of his position laid down in Bava Metzia, and there is all sorts of literature on this topic.

However, as Korban Nesanel points out, this is not actually a reversal, because according to the Rosh's girsa, Rav Nachman is arguing with Rav Assi rather than with Shmuel. Therefore, Rosh is not claiming that the halacha is like Rav Nachman over Shmuel. (I would note that this would seem to change the idea, or else clarify it, that when we say that the halacha is like Rav Nachman in dinim, this does not only apply when arguing against Rav Sheshet -- for here he is arguing with Rav Assi -- but would extend to other disputes, just not against Shmuel his Rebbe. Perhaps this is a reversal or change. Ayin Sham.)

Thus, if the Rosh had had the Rif's girsa, he would have argued with the Rif. Since he has his own girsa, he ends up ruling like the Rosh.

I wonder though about relying upon this happenstance. Rosh presumably saw Rif, and thus saw Rif's girsa which had Shmuel there instead of Rav Assi. Yet he chooses his own girsa. However, applying his own kelalei hora'ah to the Rif's girsa, he would have the opposite result. Korban Nesanel, when discussing it, puts it as "because of this" Rosh is gores Rav Assi. Was this a conscious choice so as to get a particular result? Or was he just operating upon the girsa of the gemara as it appeared in the manuscript before him?

It seems that we would have great opportunity to bolster the opposite side. How are we to decide whose girsa is correct? Let us choose Rif's girsa but Rosh's klal horaah?

Looking at the two girsaot, I presently have no spark of inspiration as to which is the original and which is derivative. But perhaps since we have a girsa one way and a girsa the other way, we should not impose obligation upon one party -- sort of like hamotzi mechavero. (We see such an idea when we cannot decide between a lishna kama and a lishna batra, in this post about Rav Zevid.)

Another point of interest. In our own gemara, we have a third girsa. Rather than Rav Assi, we have Rav Ashi as the bar plugta of Rav Nachman. This changes the game entirely. Recall that Rosh said that the idea of hilcheta kebatrai only applies to the generations of Abaye and Rava and on. Rav Ashi is just such a later generation. Therefore, given our girsa, Rosh should rule like Rav Ashi over Rav Nachman. And it is somewhat likely that the Rif would as well.

However, neither Rif nor Rosh have this girsa of Rav Ashi. We would need to start looking at manuscript evidence to see how early we can find such a variant. Rav Assi and Rav Ashi often enough switch off. Indeed, on the next daf, 66, we have the Rif have Rav Assi while our gemara has Rav Ashi. This switch-off, in both directions, happens often enough in the gemara.

And we would more expect Rav Assi, who is a contemporary, or Shmuel, who is the Rebbi, to be the bar plugta of Rav Nachman, more than Rav Ashi. But we should really look into the manuscript evidence. Tzarich Iyyun.