The Basics of Judaism: G-d & Torah: How a Halakhah becomes Accepted:
How does a Halakhah become accepted?
Any post-Biblical Halakhah is the result of a Rabbinical decision.
Until about 1000 years ago there were Rabbinical courts whose
authority was generally accepted -- for example, the Sanhedrin
in Israel or the Yeshivos in Babylonia. Decisions made since that
time may be accepted only by some communities; for example,
Sephardic Jews accept the rulings of R. Yoseph Karo in the
Shulchan Aruch, whereas Ashkenazim accept the rulings of R.
Moshe Isserles (the Rema).
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