Dear Rabbi Kornfeld,
The Gemara mentions that Shammai and Hillel had a dispute how much drawn water (mayim sheuvim) invalidates a mikva. Shammai said "hin" which the Gemara describes as exactly the way he heard it from Shmaya and Avtalyon. Then the Gemara relates that the final decision was made based on the testimony of two gardiim from the shaar haashpa. My question is, the Gemara explicitly says that Shammai also was relaying what he heard from Shemaya and Avtalyon; why did the chachamim accept the testimony of the gardiim over that of Shammai? Is it because they were two?
Gershon
You are asking an excellent question! I saw in Sefer Doros ha'Rishonim (Rav Isaac Ha'Levi, I:3:90) that writes -- because of your question -- that when Hillel said his opinion in the name of his teacher, he was not referring to Shemaya and Avtalyon (from whom he learned when he came to Israel), but to other teachers (from whom he learned when he was in Bavel). However, Rashi and the other Rishonim do not explain like this.
It must be that the Gardi'im testified that they saw this opinion practiced as Halachah le'Ma'aseh . Perhaps Hillel indeed heard from Shemaya that a "Hin" will invalidate a Mikvah, but he did not want to rely on that lenient opinion le'Ma'aseh , and he was Machmir and in practice held that three Lugin invalidate a Mikvah.