[Avodah] YT Sheni

[Marty Bluke]

R' Kohn writes:
<It is worth commenting on the very odd and obscure statement in the
gemara Beizah about YT sheni generally, that once it was enacted by a
beit din, even if the rationale for rule does not apply (given that we
are now familiar with "keviah d'yarcha" (the lunar cycles), we are not
empowered to change the edict unless a superior Sanhedrin is convened.

<This type of adherence to earlier rulings is at best an exception.

I believe it is just the opposite. The general rule is that gezeros
are lo plug. In limited situations Chazal made a gezera that is not lo
plug.

RHS explains that just like we are not darshinan taama dikra, even if
the reason for the mitzva doesn't apply the mitzva still applies on a
torah level. K'eyn dorayasa tiknu and the same applies to gezeros
d'rabbanan, we are not doresh the taam of the gezera and it applies lo
plug. However, just like on a level of d'oraysa when the Torah writes
the reason in the chumash the mitzva is regulated by that reason, so
too by gezeros d'rabbanan if the reason is written into the gezera
(which is rare) it only applies when the reason doesn't apply.

Also note, the Rambam writes (Mamrim 2:3) that gezeros d'rabanan that
were made as a s'yag so that people should not violate an issur
d'oraysa can NEVER be repealed even by a beis din that is greater
b'chochma u'bminyan. This means that according to the Rambam when
moshiach comes little will  change. We still have to observe ALL of
the s'yagim d'rabanan even if the reasons don't apply.