MARK WASHOFSKY
6. The theory, as expressed by Rambam in Yad, Sh'vitar Asor 3.3, is that minhag is valid when it chooses between permitted ritual options but cannot"permit that which is forbidden" by halakhah. See Elon op. cit., p. 738.
7. See the famous incident between Hillel and the B'nai B'teirah, B. Pesahim 66a, as well as B. Berakhot 45a("puk hazi mai ama dabar").
8. M. Avodah Zarah 1.1; Alfasi, ad loc.; Rambam , Yad, Avodat Kokhavim 9.1(on Rambam ’s differing attitudes concerning Islam and Christianity , compare Maakhalot Asurot 11.7 with Avodat Kokhavim 9.4 in the uncensored texts).
9. R. Asher b. Yehiel, Hil. HaRosh, Avodan Zarah 1.1, who summarizes the arguments. See also Hagahot Maimoniot, Avodat Kokhavim, 9.1, 2; Tosafot, Avodah Zarah 2a, s.v. asur; Or Zarua, Pisqei Avodah Zarah, ch. 1, par 95-96.
10. See Haym Soloveitchik ,"Religious Law and Change: The Medieval Ashkenazic Example," Association of Jewish Studies Review, V. 12, Fall, 1987, pp. 205-221.
11. B. Arakhin 10a and b.
12. Rambam , Yad Hanukah 3.5-6, and Sefer Hamitzvot, shoresh 1. On the other hand, Nahmanides argues that Hallel is a Toraitic commandment on the eighteen days mentioned in Arakhin; see his hasagot to Sefer Hamitzvot, shoresh 1, where he suggests that Hallel is either a halakhah lemosheh misinai or is included in the commandment to rejoice on the festivals. See also Rabad, Hasagot to Yad, Hanukah 3.6. These arguments, in turn, are rejected by R. Aryeh Lev b. Asher in his Resp. Sha’agat Aryeh(Frankfurt a.d. Oder, 1756),#69.
13. B. Ta'anit 28b.
14. B. Pesahim 117a, and Rashbam , B. Pesahim 166b, s.v., al kol pereq ufereq, etc. This distinguishes the recitation of Hallel on Rosh Hodesh from that on the concluding days of Pesah . The former is not a festival, while the latter is, and even on Hol Hamo'’ed unnecessary work is forbidden. See Rambam , quote in R. Nissim Gerondi to Alfasi, Shabbat , fol. 11a.