I hope this doesn't come out as simplistic -- I am still in the middle of trying to understand the argument between the Robonon and R. Yishmael about 1 vs 3 sets of lashes.
1. you can't learn chelev simply from an ox because of the gezeirah shava. you can't learn chelev simply from kesev because of the difference in the tail fat. there is no explicit reason given not to learn chelev from a goat. why not?
1a. if you rely on the distinction between goats and other animals vis-a-vis idolatry as evidenced in the "tzrichei" explanation, then why not use that same tzrichei for shor in the first place? why did they first have to use the gezeirah shava for shor?
2. why doesn't r. yishmael say that the text could have said "beheimah"? this would have included the proper animals and excluded others. since the text does not say "beheimah" but lists the 3 animals, learn out 3 sets of lashes.
Dan Rosen, teaneck, NJ
1) That is a good question. Here are two possible answers:
(a) After the Gemara makes the Tzerichusa, we no longer need the answer of Shor-Shor mi'Shabbos. But before that point, there is nothing wrong with using Shor-Shor mi'Shabbos as a first solution. Alternatively, the Gezeirah Shavah of Shor-Shor is stronger than the Tzerichusa. Shor-Shor includes even Chayah (since it is a Gezeirah Shavah and no questions can be asked on it), but if the Torah would have said Keves or Ez alone, we would not be able to learn other animals out from there.
2) The word Beheimah cannot exclude Chayah, since Chayah is generally included in the word Beheimah (Bava Kama 54b).
All the best,