ANSWERS TO REVIEW QUESTIONS
prepared by Rabbi Eliezer Chrysler
Kollel Iyun Hadaf, Jerusalem
Previous dafEruvin 14
ERUVIN 11-15 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.
(a) If one wished to support an Ari'ach on a Koreh of a Tefach, one would
simply add a layer (of a thumb-breadth - see Rabeinu Chanan'el) of cement on
either side of the Koreh - Consequently, a Koreh of one Tefach will suffice
to hold an Ari'ach.
(b) According to Rabah bar Rav Huna, the posts that support the Koreh do not
need to be strong enough to support the Koreh and the brick (only the Koreh)
- since it is *the Koreh* that needs to support the brick, and not the posts
which support it.
(c) One may not carry in a Mavoy whose Koreh one covered with a mat, which
extended downwards, but stopped three Tefachim from the ground - because the
Mavoy has neither a Koreh (since it is covered), nor a Mechitzah, since it
stopped`three Tefachim short from the ground, in which case we cannot apply
(a) If a Koreh which extends from one wall across the Mavoy, but falls short
of the opposite wall, or two Koros which come out of the two walls, but
which do not quite meet in the middle - one is permitted to carry in the
Mavoy, provided the Koreh in the first case reaches to within three Tefachim
of the wall, and in the second, the two Koros are within three Tefachim of
each other. Otherwise, a second Koreh is required to rectify the fault.
(b) According to the Tana Kama, two parallel poles, neither of which can
support a half-brick (i.e. is a Tefach wide) - form a Kasher Eruv, and
permit one to carry in the Mavoy, provided their combined width is at least
one Tefach, and they are withim three Tefachim of each other.
(c) Raban Shimon ben Gamliel holds that the two poles must be able to hold
an Ari'ach three Tefachim lengthwise (i.e. they must have a combined width
of at least three Tefachim), before carrying in the Mavoy is permitted.
(a) Rebbi Yossi b'Rebbi Yehudah maintains that, if the two poles are at
different heights - the Mavoy is nevertheless Kasher, because we consider
the top pole to be slightly lowered, and the lower pole to be raised (until
they are both of the same height).
(b) We do not say 'Ro'in' - when one of the poles is either above twenty
Amos or below ten Tefachim.
(c) Rebbi Yossi b'Rebbi Yehudah holds like his father (in our Mishnah), who
says 'Ro'in, though he disagrees with him with regard to a Koreh which is
higher than twenty Amos, which his father permits, but he invalidates.
(a) When Rav Yehudah quoted our Mishnah as saying 'Rebbi Yehudah Omer,
Rechavah, Af al Pi she'Einah Beri'ah' - Rav instructed him to change the
text to 'Rechavah u'Beri'ah' (see Tosfos DH 'Asnayah').
The Chidush of 'Agulah, Ro'in Osah Ke'ilu Hi Meruba'as' - lies in the
continuation of the Mishnah 'Kol she'Yesh be'Hekefo Sheloshah Tefachim, Yesh
Bo Rochav Tefach'.
(b) This is not the case, when the Koreh is four Tefachim wide, because then
it does not matter if it is too weak to actually support a brick.
(c) Initially, the Tana quoted Rebbi Yehudah as holding 'Ro'in' by wood for
example, which is usually sufficiently strong to support a brick - he then
adds the Din of 'Ro'in' by straw, to teach us that Rebbi Yehudah holds
'Ro'in' even by something which is usually not strong enough to hold a
(d) Even if the Koreh bends upwards to above twenty Amos, it is obvious
that, according to everyone, if less than three Tefachim were to remain if
one discounted the excess section, the Mavoy would be Kasher. The Chidush in
our Mishnah is if the Koreh extends outwards, that, if the two remaining
ends of the Koreh were less than three Tefachim from each other after that
section was removed, the Mavoy is Kasher - to teach us that Chazal did not
decree carrying in the Mavoy, for fear that may just follow the section that
protruded into the street, and carry there.
(a) We learn from the 'Yam shel Shlomoh' - the principle that whatever is
three Tefachim in circumference, is one Tefach in diameter.
(b) By 've'Ha Ika Sefaso' - the Gemara means to ask query this principle:
The diameter of the Yam shel Shlomoh contends with the space alone, whereas
the circumference also includes the thickness of its walls; so how can we
connect the two?
(c) The Gemara answers - that the walls of the Yam shel Shlomoh were
extremely thin, like the petals of a Shushan rose, so they did not really
add much to the circumference.
(d) This answer however, is inadequate, because, however thin the Yam was,
it must have measured something, which means that the proportion of diameter
to circumference is not exactly one to three.
(a) A Mikvah must contain - forty Sa'ah of water (three Amos by one mah by
one Amah) in order to be Kasher.
(b) Four hundred and fifty cubic Amos would have sufficed to make a hundred
and fifty Mikva'os (whereas the Yam shel Shlomoh contained five hundred
(c) The Kashya is a fallacy however - because the four hundred and fifty
cubic Amos would be correct if we were talking about a *square* Mikvah,
whereas the Yam shel Shlomoh was circular (meaning a circle contained inside
(d) A square is a quarter more than a circle (i.e. three cubic Amos for
every four), in which case, assuming the Yam shel Shlomoh to have been
totally circular, the 'Yam' should have contained three hundred and seventy-
five cubic Amos (making *a hundred and twenty-five* Mikva'os (and not a
*hundred and fifty*!)
(a) In fact, the Gemara concludes - the bottom three Amos were square, and
the top two, round.
(b) It cannot have been the *top* section of the 'Yam' that was square -
since the Pasuk writes "Sefaso Agul".
(c) The bottom three square Amos totaled three hundred cubic Amos - making
one hundred Mikva'os), and the top two, round Amos, totaled a hundred and
fifty cubic Amos - making fifty Mikva'os.
(a) Two thousand Bas is the equivalent of six thousand Sa'ah which, in turn,
is the equivalent of one hundred and fifty Mikva'os - This proves the shape
of the 'Yam shel Shlomoh, as we just described it, and dismisses the
Gemara's suggestion that maybe it was just the top *Amah* (and not *two*)
that was round.
(b) When the Pasuk in Divrei ha'Yamim gives the volume of the 'Yam' as
*three* thousand Bas - it is referring to the volume of solid contents,
which is one third more than the liquid (due to the extra amount of solids
that one is able to heap by a solid, but not by a liquid.
(c) A cupboard or a large container holding forty Sa'ah of liquid or sixty
Sa'ah of solids - is no longer subject to Tum'ah, because, due to the fact
that it is too heavy to be carried full as well as empty, it is no longer
considered a K'li.
(d) The Gemara proves from this Mishnah - that one normally heaps one third
more of solids into a vessel than one does liquid (as we just stated).
(a) A Lechi must be - at least ten Tefachim tall.
(b) According to Rebbi Yossi - the minimum width of a Lech is three
(c) No! The fact that our Mishnah speaks of 'Lechayin' in the plural - does
not mean that the author must be Rebbi Eliezer, who requires two Lechayayim
for a Mavoy. In fact, the author of our Mishnah could just as well the
Chachamim, and 'Lechayin' refers to Lechayin in general.
(d) On account of this Kashya (why then, does the Tana refer to 'Koreh' and
not to 'Koros') the Gemara interprets the Tana's use of the of 'Lechayin' in
the plural in connection with the Machlokes between Rebbi Eliezer and the
Chachamim concerning Lechayin (whether a Mavoy requires one Lechi or two):
those Lechayin over which Rebbi Eliezer and the Chachamim dispute there,
must be ten Tefachim tall.
(a) A Chut ha'Sarbol - is the thread with which one ties together the front
ends of a coat.
(b) The Chidush of the Beraisa, which permits carrying in the inner of the
Mavoy if one placed a Lechi half-way - is that we do not forbid carrying
there, for fear than one may forget and carry in the entire Mavoy (even in
the section which has no Eruv).
(c) A Lechi that stops between three and four Tefachim short of the ground
is not Kasher, even according to Raban Shimon ben Gamliel, who holds Levud
up to *four* Tefachim - even Raban Shimon ben Gamliel agrees that a gap of
three Tefachim between the bottom of the Mechitzah and the ground will
invalidate a Mechitzah, since it is one which allows kid-goats to get in
(a) The Gemara felt inclined to rule like Rebbi Yossi with regard to the
width of a Lechi - since Rebbi here follows the opinion of Rebbi Yossi; and
also because of the principle 'Rebbi Yossi Nimuko Imo' (meaning that Rebbi
Yossi was renowned for his sound reasoning) - though this second reason is
not confined to our Machlokes.
(b) We do not, in fact, rule like Rebbi Yossi (neither here, nor by Hilmi -
making salt-water on Shabbos, where he is strict) - because of the universal
custom to permit a Lechi of any width.
(c) Rebbi Tarfon is referring to a Berachah *Rishonah* - when he prescribes
'Borei Nefashos' as the Berachah for water.
(d) We do not follow the ruling of Rebbi Tarfon, with regard to the Berachah
Rishonah over water, because of the universal custom to recite 'Shehakol'