it is difficult for me to understand the question that R.Shrabia asks Abbaye. The Braita is bringing a limud of Klal hatzarich le prat ve prat hatzarich leklal,to define what Bechor really means,so that we do not have really two bavot,but actually one single limud.
why is it a difficulty to start with an assumption that bechor le davar echad is a bechor, and then reach the conclusion that it is not?
thank you,
Alberto Djmal
Dear Alberto,
Please excuse my delay in answering. Regarding your difficulty with Rav Shravya's question: The Gemara initially thought that 'Peter Rechem' comes to exclude a male animal that was born after a female. (However if it was born after a Yotze Dofen - even a male Yotze Dofen, it would be a Bechor). In other words, the Beraisa holds that a Bechor for one thing (although it was not the first male to be born), is nevertheless a Bechor. Now, this is not a stage in the Beraisa's chain of thought because if it was, then why did the Gemara not immediately quote the Pasuk "Bechor", to preclude a male animal that was born after a female? And "Bechor" is a better Drashah than "Peter Rechem", because it will also tell us that a Bechor for one thing is not a Bechor (in which case, the Gemara would not have been able to ask its next question - froma male born after a Yotze Dofen).
So it does appear as if the Beraisa actually holds that a Bechor for one thing, is a Bechor. But then the Gemara goes on to ask the question on a male born after a Yotze Dofen, and it answers from "Bechor", from which we are forced to say that the Beraisa holds that a Bechor for one thing is not a Bechor - and it retracts from its original question in such a way that it could not possibly have answered with the Pasuk "Bechor". It is not a male that was born after a female, which the Beraisa is trying to learn out (which caused us to ask :'Why does the Gemara not ask from Bechor?'), but a male that is itself a Yotze Dofen. On this, the Beraisa could not have quoted "Bechor", since he is , in fact, a Bechor in every respect - the only Pasuk it could have quoted was "Peter Rechem".
From now on, the Gemara's asks precisely like you asked: What will happen if the male is born after a Yotze Dofen, do we say that a partial Bechor is a Bechor or not - Something which was not discussed in the Beraisa till now. And it answers from the word "Bechor", that it is not a Bechor.
I hope that I have clarified the Sugya sufficiently.
be'Virkas Kol Tuv,
Eliezer Chrysler.