THOUGHTS ON THE DAILY DAF
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ERUVIN 77 - sponsored by a generous grant from an anonymous donor. Kollel Iyun Hadaf is indebted to him for his encouragement and support and prays that Hashem will repay him in kind.
1) A WALL BETWEEN TWO CHATZEROS, THE TOP OF WHICH IS LESS THAN 4x4
QUESTION: Rav and Rebbi Yochanan argue concerning the status of the top of
a wall between two Chatzeros, when the top of the wall is less than four
by four Tefachim. Rav says that both Chatzeros have use of the top of the
wall (since it is not an independent domain in itself), and therefore it
is forbidden to carry even on top of the wall as in any shared domain not
combined through an Eruv. Rebbi Yochanan says that each Chatzer may use
the top of the wall since it is a Makom Petur.
2) DIMINISHING THE HEIGHT OF A WALL
The Gemara challenges Rebbi Yochanan's opinion from the Mishnah, which
says that the residents of each Chatzer may use the top of the wall, but
they might not carry things between the wall and their Chatzer.
What is the Gemara's question? The Mishnah is clearly discussing a case
where the top of the wall is larger than four by four Tefachim, as the
Mishnah states explicitly, while Rebbi Yochanan is talking about a wall
less than four by four Tefachim! And if, for whatever reason, there is a
valid question on Rebbi Yochanan from our Mishnah, then it should also be
a valid question on Rav (who said that the top of the wall may not be used
(a) TOSFOS (DH Olin) answers that the Gemara knew all along that Rav's
reasoning is that "both domains (the two Chatzeros) have dominion over the
top of the wall," and therefore as a shared domain, it is forbidden to
carry there. That applies only when it is less than four Tefachim. When it
is four by four Tefachim, though, it is an independent domain unto itself
and one may carry atop it, as the Mishnah states. The Gemara's question is
on the opinion of Rebbi Yochanan. The Gemara initially thought that the
reason Rebbi Yochanan permitted the residents of both Chatzeros to carry
atop the wall is because it is not convenient for either of them to use of
the top of the wall, and therefore neither Chatzer has dominion over it.
If that is Rebbi Yochanan's reason, then it should apply just the same
when the top of the wall is four by four Tefachim, because it is still
difficult to climb up and use and it should still be considered a separate
domain from each Chatzer.
The Gemara answers that Rebbi Yochanan's reasoning is not that it is
difficult to use the top of the wall and therefore it is a domain unto
itself, but that it is a Makom Petur. If it is wider than four Tefachim,
it is no longer a Makom Petur and it is forbidden to transfer between it
and the Chatzer because it is a separate domain unto itself.
(b) The CHIDUSHEI HA'RAN answers as follows. The Mishnah says that when
the top of the wall is four by four Tefachim, each person may go up to the
top of the wall and eat items that were already there, as long as they do
not take anything down from the top of the wall. The words of the Mishnah
seem to imply that the emphasis is on the Heter, that is, on what it is
*permitted* to do. From that the Gemara infers that had the wall not been
four by four Tefachim, it would have been completely forbidden to use the
top of the wall, but now that it is four by four, there is a Heter to use
According to Rebbi Yochanan, who says that when it the wall is less than
four by four one is permitted to eat on top of the wall and to bring food
there, the Mishnah should have focused on the *Isur* and said, "One may
*not* bring food up and eat it, but one may go up and eat food that was
already there," placing the emphasis on what one may *not* do.
QUESTION: The Mishnah (76b) states that a wall which is at least ten
Tefachim high between two Chatzeros is considered a separate Reshus from
each Chatzer and the residents of the Chatzeros may not carry to or from
the top of the wall. The Gemara says that if one wants to decrease the
height of the wall to within ten Tefachim (making it permissible for the
two Chatzeros to make an Eruv together and then to carry from each Chatzer
to the top of the wall, -RITVA), one may do so by placing a mound of earth
that is at least four Tefachim long (-RASHI; according to TOSFOS 77b, DH
Im, it must also be four Tefachim wide) at the bottom of the wall. If the
height from the top of the mound until the top of the wall is less than
ten Tefachim, then the mound serves as an entranceway to the top of the
wall and the entire length of the wall may be used. If the mound is less
than four Tefachim long, then only the actual section of the wall against
which the mound was placed may be used.
The Gemara asks that if a mound less than four Tefachim suffices, then it
should permit the use of the entire length of the wall. If it does not
suffice, then it should not even permit the use of the small section of
wall under which it lies. Ravina answers that the Gemara is referring to
when one removed a brick from the *top* of the wall. In such a case, if
the removal of the brick diminished the height of the wall to less than
ten Tefachim only along a section of the wall that was less than four
Tefachim long, then that section of the wall is permitted to use, but not
the rest of the wall.
How does this answer the Gemara's original question? What difference does
it make if the decrease in height of the wall occurs as a result of
raising the floor at the bottom of the wall, or lowering the height of the
wall? If a mound of less than four Tefachim at the bottom of the wall does
not help at all, then why should it help when the top of the wall is
lowered by the amount?
(a) RASHI (DH Amar Ravina) seems to explain that when the decrease occurs
at the top of the wall, even though it might not be considered an
entranceway (since it is less than four Tefachim), it still serves to
lower the wall at that point, and thus that section of the wall may be
used. However, when a mound is placed at the bottom of the wall to
decrease the wall's height, the wall itself is not actually affected
because it is still ten Tefachim high (when viewed from the other side).
Therefore, the section directly above the mound may not be used because it
is still ten Tefachim high.
(b) The RASHBA and ROSH (7:1, near end) explain that a mound less than
four Tefachim long at the *bottom* of the wall is not large enough to
balance one's self on in order to use the top of the wall. Therefore the
top of the wall is still considered to be ten Tefachim high. A small gap
at the *top* of the wall, though, can easily be used by standing on the
Perhaps the Rashba and Rosh did not accept Rashi's explanation, because
they understood that the Gemara was discussing a case of decreasing the
size of the wall *from both sides* in order to make a Halachic passageway
between the two Chatzeros, which would permit the two Chatzeros to make
one Eruv together (as the RITVA writes).
Rashi, on the other hand, understood the Gemara not to be referring
specifically to two Chatzeros that want to decrease the height of the wall
between them, but even to one Chatzer which wants to decrease the height
of a wall next to it (regardless of what is on the other side of the wall)
in order to use the top of the wall on Shabbos. Therefore, the mound
placed on one side does not serve to decrease the height of the wall,
since it is still ten Tefachim high on the other side.