In the Mishna on 76b, R' Shimon allows a Mitzri or Edomi Giyoret to marry an ordinary Jew immediately. The Chachamim tell him that they will accept this if he has a tradition from his Rabbanim, and he replies that he indeed has such a tradition. Nobody challenges this (the Gemara discusses only R' Shimon's kal va-chomer, which is the weaker of his two proofs) - and yet the Halacha does not follow R' Shimon (Rambam on Mishna, Ran). Why?
Joachim Mugdan, Basel, Switzerland
The Maharsha (Mahadura Basra) on 77b explains that Tosfos was bothered by this question and answered that the Chachamim meant to tell Rebbi Shimon that they will accept his postion if he has a Kabalah Halachah l'Moshe mi'Sinai. However,when Rebbi Shimon replied that he was saying a Halachah he did not mean a Halachah l'Moshe mi'Sinai, only that he was Mekabel this Psak from his Rebbe'im. It is possible to learn like this in the Ran although I concede that the words of the Ran do not appear to point in this direction.
The Ya'avetz also asks this question but does not offer any answer.
Reb Zvi Hersh Kalisher offers an explanation based on a lenghty Pilpul, see his Hagahos printed at the back of most Mishnayos.
Dov Freedman