QUESTION: Abaye explains that he was unable to make a Shituf in his Mavoy.
The Gemara asks why he did not simply take a barrel of vinegar and be Makneh
a Revi'is of vinegar to everyone in the Mavoy, and that way he would make a
valid Shituf! Abaye answers that a Shituf cannot be made with food that is
in a barrel in storage, since we hold that Bereirah does not work ("Ein
Bereirah"). That is, it is not possible to determine which specific portion
of the vinegar in the barrel belongs to which member of the Mavoy *until*
the members of the Mavoy actually take for themselves a portion; there is no
*retroactive* determination.
The Gemara challenges Abaye from a Beraisa which states that a Shituf *can*
be made with food that is in storage. Rav Oshiya answers that the Beraisa is
the opinion of Beis Hillel, who holds that Bereirah does work, while Abaye's
ruling is the opinion of Beis Shamai, who holds "Ein Bereirah." Rav Oshiya
cites as a source for the respective opinions of Beis Hillel and Beis Shamai
from a Mishnah in Beitzah discussing a case of a Mes in a house with many
doorways. (The Mes causes all of the vessels in all of the doorways to
become Tamei. Beis Shamai maintains that opening one of the doors does *not*
remove the Tumah retroactively from the other entranceways. Beis Hillel, on
the other hand, says that opening one of the doors *does* remove the Tum'ah
retroactively from the other entranceways.)
According to Beis Hillel, Bereirah works, and in the case of the Eruv,
presumably he would hold that one may be Makneh a Revi'is of vinegar to
everyone in the Chatzer. If so, why did Abaye refrain from making the
Shituf? Could it be that he ruled like Beis Shamai?!
ANSWER: TOSFOS (DH Tanya) answers that Abaye learned the Mishnah in Beitzah
differently. He learned that the case of the Mes in the house with many
entrances has nothing to do with Bereirah, and Bereirah was not the subject
of a Machlokes between Beis Shamai and Beis Hillel. Rather, the subject of
Bereirah is a Machlokes among many other Tana'im, as we find earlier in the
Maseches (36b-37a), and Abaye ruled like the opinion that says Ein Bereirah.