Tosefet Shabbat/ Yom Tov

Tosfot in Pesachim (99b) says if one accept the holiday of Pesach early the mitzvah of eating matzah can not be fulfilled during tosefes yom tov because there is a hekesh from matzah to korban pesach where the possuk says it must be eaten after nightfall and during tosefes yom tov it is not yet night.  Rav Elchonon Wasserman points out that if not for the hekesh Tosfos holds that you would be able to fulfill the mitzvah of eating matzah during tosefes yom tov even though it is still the 14^th of Nissan.  How can one fulfill the mitzvah of matzah if it not the Yom Tov yet?  We see, Rav Elchonon says, that Tosfot holds tosefes yom tov makes it as if the chol day ended and the yom tov day started and therefore it is considered eating matzah on Pesach.  Rav Elchonon asks this contradicts Tosfot in Ketubot (47a) that says tosefes yom tov only creates an issur meleacha like that of the yom tov but the din of simcha is not extended.  That Tosfot holds that tosefes yom tov only extends the issur melecha but does not extend the yom tov itself.  In other words the two Tosfot are arguing in the chakirah of the Amek Beracha (Yom Tov) if tosefes yom tov merely extends the issur melacha or the yom tov itself is extended. 

The Gemarah in Berachot (27b) says that one can make kiddush of Shabbat during tosefes Shabbat.  Is tosefes merely adds an issur melacha how does that work?  (According to the Rambam discussed here, that holds one can say kiddush before Shabbat this is not difficult.) The Mishne Berurah (267:5) cites a machlokes if one can fulfill the mitzvah of seudat shabbat during tosefes.  If one can fulfill kiddush, why not seudah?  

The Rama in Yoreh Deah (196:1) cites a machlokes in a scenario where the community accepted Shabbat early and a woman forgot to do a bedikah Friday can she still do the bedikah or is it considered that Friday is over and she missed it.  The two opinions seem to be arguing in the same machlokes as the two Tosfot.  The Gra explains the opinion that you can do a bedikah is because tosefes only makes it considered nightfall regarding kiddush and havdalah as stated both the Tosfot in Pesachim and in Ketubot.  How does tosefes only make it nightfall vis-a-vis kiddush and havdalah?  And how can the Gra lump together the Tosefot in Pesachim and the Tosefot in Ketubot when they are two different opinions? 

Rav Chayim (stencil) asks on the Tosfos in Pesachim that tosefes only extends the yom tov for dinim that stem from the kedusha of the yom tov but matzah is a separate mitzvah?  What is Rav Chayim's question, what difference does it make if the mitzvah is that of the kedashu of the yom tov or a separate mitzvah?   

The Minchas Chinuch (19:9) says that if one has a meal at the end of Pesach that extends past the end of the chag then one may eat chametz in the meal once the chag ends even though the individual is doing tosefes yom tov because tosefes only creates an issur melacha but the kedusha of the yom tov does not extend.  He repeats this yesod in mitzvah 323:2.  The Minchas Chinuch holds like the way Rav Elchonon learnt in the Tosfos in Ketubot.  The Alter Rebbe rules the same way as the Minchas Chinuch in Shulchan Aruch (491:3.)  However, he explains the reason differently.  He explains that tosefes yom tov extends the kedusha of the day into the timeframe of chol (either before or after the chag,) so dinim of kedushat hayom apply but chametz is not an issur which derives from the kedusha of the day (it applies on chol hamoad,) but stems from the days of Pesach themselves.  We see from the Alter Rebbe a third way to understand tosefes shabbos/yom tov.  It is not just an issur melacha but on the other hand it doesn't make the chol truncated and it is as if the day of yom tov grew longer.  Rather what tosefes does is to extend the kedusha of the chag into the chol.  The yom tov itself doesn't extend, it is the kedusha of the yom tov which is extended.  That is what Rav Chayim meant to ask.  Matzah has nothing to do with the kedusha of the yom tov, it is a separate mitzvah so how can Tosfot entertain that one can eat matzah during tosefes?  This is the intent of the Gra as well.  Kiddush and havdalah are mitzvot which derive from the kedushat hayom.  Those mitzvot can be fulfilled during tosefes.  However, the specific mitzvot to the chag have nothing to do with kedushat hayom, they are separate mitzvot and one can not fulfill them during tosefes.  This means that it is not considered to actually be shabbos/ yom tov during the time of tosefes and hence a woman can do her Friday bedikah during tosefes shabbos.  This is why some poskim hold that seudat shabbat can not be fulfilled during tosefes shabbos because they hold the seudah is a mitzvah that has to be done on shabbos, it is not a mitzvah linked to the kedusha of the day.  This is how the Gra understood the two Tosfot.  He understood that they are not two distinct approaches to the understanding of tosefes yom tov but rather they are saying the same yesod that the the the previous day is not chopped off and it is considered nightfall early, rather tosefes only extends the kedusha of the day.  (We will have to say that Tosfot held not like Rav Chayim and matzah is a mitzvah which does stem from the kedushat hayom.)  

(This approach is not like the Maharshal and Taz in siman 668:1 and the Taz in 494:1, ואכ"מ.) [Based upon a shiur by R' Elefant of the Mir.  Many of the points mentioned here were discussed on my father's blog 16 years (!) ago here.]