Thank you so much for getting back to me.
I have been working through dafka this Daf and in tears trying to understand the following
"Meshum De Kasha Lay" - that Abbia has on Rav Asisi. I think I have now got Peshat but it is very difficult. My chavrusah and I have spent a whole week on this Amed - I went to shiur on Thursday night and got so lost!!!
Over Shabbos I did Chazorah and I think I now understand it - any help will be greatly appreciated
If you followed the sugya until that point you should not have trouble with understanding Abaye.
After the Gemara established that the reason we do not return the Shtar if it has Achrayus even though the Loveh is Modeh is because we are afraid that it is a Shtar Mukdam, the Gemara asks that if so how can we ever write a Shtar before the actual loan is executed, since if they actually use the Shtar it will be a Shtar Mukdam and the Malveh will be able to defraud the Lekuchos. To this Rav Asi answers that we can only write a Shtar Hakna'ah before the loan, for in a Shtar Hakna'ah -- since the Loveh already was Makneh his property to the Malveh even though the loan did not take place yet -- the Malveh will be able to legitimately collect from the time written in the Shtar.
The Gemara then retorts that if this is true -- that the only type of Shtar we allow the Loveh to write before the loan is a Shtar Hakna'ah -- then we have then lost our Pshat in the Mishnah, for the whole problem with the lost Shtar was that maybe it was written before the actual loan, but if it is not a Shtar Hakna'ah then what are we afraid of? We do not write non-Hakna'ah Shtaros before the loan is executed! To this the Gemara answers that since it was a lost Shtar we are more suspect and we are afraid that the Loveh deviated and wrote a non-Hakna'ah Shtar before the loan.
Hopefully the flow of the Gemara until this point is clear.
Abaye says that even non-Hakna'ah Shtaros can be collected from the time they are written, even if the loan did not take place at that time, for we do not need to write the Kinyan into the Shtar since it is the Edim who make the Kinyan for the Malveh with their signatures (in other words, the Shtar itself is a Kinyan and does not need a separate Kinyan). The reason he does not accept Rav Asi's approach is "Mishum d'Kashya Lei" -- he does not accept the Teirutz of Rav Asi who says that although we do not write Shtaros which are not Shtaros Hakna'ah, the Mishnah is worried that it happened anyway. This leaves him without a Pshat in the Mishnah at this point. The Gemara eventually says that he learns that the problem in the Mishnah is that we are afraid that it was a legitimate Shtar that was actually paid and now the Malveh and the Loveh are trying to cheat the Lekuchos.
D. Zupnik