[Avodah] Yom Kippur on Shabbos: Kiddush?

[Zev Sero]

On 11/08/2013 9:06 PM, Kenneth Miller wrote:
> I understand from Aruch Hashulchan 271:2 that accrding to Rashi and others, there is a Chiyuv d'Oraisa to say Kiddush Al Hakos. That is, if one merely says "Baruch... Mekadesh HaShabbos" in the Amidah, he has still not been yotzay the mitzvah of Zachor Es Yom HaShabbos L'Kadsho, and still needs to take a cup of wine and say kiddush over it.
>
> My question: How do these views deal with the situation when Yom Kippur falls on Shabbos? I can easily see how a takana d'rabanan would allow for exceptions for such situations. But in my experience, d'Oraisas are very straightforward, and do not allow for exceptions.
>
> What would Rashi have us do? Does he (or anyone else) address this? Is it a simple case of Lav Docheh Aseh (which I think is actually the reverse of the halacha), or is something else at work here?

There are many mitzvos de'oraisa where the Torah doesn't specify how the
mitzvah is to be done, and the chachamim prescribed a particular method;
mid'oraisa one could still do the mitzvah in some other way, but mid'rabanan
the mitzvah d'oraisa is to be done only in this way.

A common example is benching, where the Torah doesn't prescribe any
particular nusach, and the chachamim, starting with Moshe and concluding with
David & Shlomo, decreed a nusach one must use.  The later chachamim who added
the fourth bracha could have made it d'oraisa too, just as the earlier
chachamim had done with their brachos; I don't know why they chose not to.

Kiddush, according to many rishonim, is the same: the chachamim decreed that
one must fulfil ones d'oraisa obligation over wine.  If one said "mekadesh
hashabbos" with the specific kavanah of fulfilling ones chiyuv d'oraisa it
would still *work*, but one would be violating the chachamim's decree not to
do so.  On yom kippur they didn't make this rule, so it remains as it was
before they came along, and one is yotzei with a verbal mention.

-- 
Zev Sero               A citizen may not be required to offer a 'good and
zev at sero.name          substantial reason' why he should be permitted to
                        exercise his rights. The right's existence is all
                        the reason he needs.
                            - Judge Benson E. Legg, Woollard v. Sheridan