[Avodah] You can't just change accepted practice

[Micha Berger via Avodah]

I thought this would be an interesting topic to collect sources for.

1- The best known case is probably the Rambam on counting years toward
shemitah. In Shemitah veYovel 10:2-4 the Rambam calculates when shemitah
would fall out, and he gets that churban bayis sheini would have been
mota'ei shevi'is. Although in hal' 5 he notes that the ge'onim has a
tradition that they didn't count yovel during galus Bavel nor after
chuban sheini "zeh shehu qabalah".

The Rambam says that lehalakhah, accepted practice trumps sevarah.

2- The case I encountered a couple of weeks back in AhS Yomi was YD 61:53.
The gemara establishes that the accepted pesaq in their day was to give
the matenos kehunah from each animal even in Bavel (see Shabbos 10b
and Rashi sham). The AhS says that even so, we see around us that we do
not hold by that pesaq, and we can continue not to give matenos kehunah
from animals shechted in chu"l -- keneged the gemara! (But if you do,
lo michzei keuhara.)

Presumably this is because the gemara's conclusion was itself based on
what was nahug.

But in both cases, mimeticism trumped textualism. (Insert here diatribe
about mesorah and preserving the momentum of halachic development.)

Tir'u baTov!
-Micha

-- 
Micha Berger             I slept and dreamt that life was joy.
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