Why, when in doubt, do we assume that the egg was laid before Yom Tov? Since
the Gemara is discussing a case where there is no rooster in the vicinity,
there is a possibility that the egg was laid at night on Yom Tov, and thus
it should be a Safek when the egg was laid! As such, it should be Asur
because of the Safek (since it is a Davar she'Yesh Lo Matirin)!
(a) TOSFOS (DH Ki Lo Badak) answers that most eggs are born during the day
(even if they are Safna me'Ar'a), and therefore we do not have to take into
consideration the small chance that it was laid at night, unless we know
that the chicken coop was empty of eggs before Yom Tov. This is also what
RASHI (DH Eima) writes, as well as other Rishonim.
This answer, though, is problematic, because we learned earlier (4a) that
even though most of the eggs in a mixture are permitted, we prohibit the
entire mixture because a "Davar she'Yesh Lo Matirin" is not Batel. Here,
too, the egg should not be permitted just because most eggs are laid during
The answer to this question is that the principle of "Davar she'Yesh Lo
Matirin" only makes the items Asur when it is *known for certain* that at
least one item in the group is Asur ("Ischazek Isura") and now a Safek has
arisen which one it is; for example, it fell into a mixture with more Heter
than Isur. However, if there is a "Rov" working to permit the item, and the
item was never known to be certainly Asur (it was only a Safek), then it is
Mutar and the principle of "Davar she'Yesh Lo Matirin" does not prohibit it.
Alternatively, in this case it is not merely a chance "Rov" which tells us
that the egg was laid during the day and thus should be Mutar. Rather, it is
a naturally occurring process ("eggs are normally laid by day"). Such a pre-
determined Rov may prove to us that the egg was born during the day.
(b) The RIF omits the Halachah of Rebbi Yosi ben Shaul, who says that when
there is no rooster in the vicinity and one checked the nest before Yom Tov,
the egg that is found there on Yom Tov morning is Asur. From the words of
RABEINU YEHONASAN M'LUNIL it seems that he feels according to the Rif that
even if one did *not* check the nest before Yom Tov there is still a Safek
when the egg was laid, and it is Asur because of that Safek (not like
However, the Gemara states clearly that if one did not check the nest before
Yom Tov, the egg is *Mutar*! How does the Rif explain the Gemara?
The Rif learns that this Gemara is in accordance with the opinion of Rav
Papa (3b) who maintains that a Safek "Davar she'Yesh Lo Matirin" is *Mutar*
in the case of a Safek d'Rabanan, in contrast to the opinion of Rav Ashi
(4a). Since the Halachah follows the opinion of Rav Ashi regarding a Safek
d'Rabanan which is a "Davar she'Yesh Lo Matirin" (and it is Asur), the egg
in this case, too, will be Asur.
This also seems to be the opinion of the RAMBAM (as the TZELACH (7b) points