Mahretz Chayes (Toras Neviim #3 Maamar Lo Sasur): The Kesef Mishna (Mamrim 2:1) raises a very strong question against the Rambam. The Rambam says that where there is a dispute based on sevora or drasha concerning a Torah law, a later generation can reject the view of an earlier generation - even though it is not greater in wisdom and number. If so then why don’t Amoraim disagree with Tannaim and in fact we find many instances that an Amora’s view is rejected because his view differs from that stated in a Mishna or braissa. The Kesef Mishna answers, “It is possible to say that from the day that Mishna was completed it was accepted and established that later generations would not be permitted to disagree with the earlier generatons. Similarly when the Talmud was completed, no one had the right to disagree with it.” But there is no evidence in either the Talmud Bavli or Yerushalmi that there was such binding agreement. One can not find the slightest hint in the Mishna or Talmud and the Kesef Mishna’s questions are very solid… However I saw something similar in the Rambam’s Introduction to the Mishna Torah, “However all those matters that are found in the Babylonian Talmud are obligatory for all Jews and they can be forced to observe them… And all these matters were agreed to by all Jews.” We see that the Rambam also writes the reason for the obligation is that all Jews agreed to it. However I don’t know where there is evidence that such an agreement occurred.