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Eruvin 50

ERUVIN 49 & 50 - have been dedicated jointly by the Feldman family to the memory of Hagaon Rav Yisroel Zev [ben Avrohom Tzvi] Gustman Ztz"l (Vilna- N.Y.-Yerushalayim).


SUMMARY: Rav says that if one attempts to make his Makom Shevisah underneath a tree without specifying in exactly which four Amos his Shevisah will be, he is not Koneh Shevisah anywhere, not underneath the tree nor in his present location. Rabah explains that Rav's reason is because of the principle, "Kol she'Eino ba'Zeh Achar Zeh, Afilu be'Bas Achas Eino" -- two actions which do not take effect when done consecutively, one after the other, also do not take effect when done at one time. Since one cannot make an additional Makom Shevisah of four Amos if one already made a Makom Shevisah, he also cannot make his Makom Shevisah underneath the tree because of that principle.

The Gemara explains that Ma'aser, though, is different. When one attempts to separate 20% (instead of the prescribed 10%), nevertheless 10% becomes Ma'aser, even though if one first separated 10%, he cannot separate another 10%. The Gemara explains that the reason is because since Ma'aser can be separated from half of each grain, when one separates 20% it is as if he intends to separate one out of every two grains that he designated.

What does the concept of "Kol she'Eino ba'Zeh Achar Zeh..." have to do with our Mishnah? The person making his Eruv Techumin does not want *all* eight Amos underneath the tree to be his Makom Shevisah; he only wants four of those eight to be his Makom Shevisah! If so, how can it be called, "be'Bas Achas," as if he wanted to make *two* Shevisos?

Furthermore, what is the logic of the Gemara when it says that since one can separate Ma'aser by separating halves of grains, the concept of "Kol she'Eino ba'Zeh Achar Zeh..." does not apply?

ANSWER: When one does not specify where his Makom Shevisah should be but instead designates that four out of a certain eight Amos should be his Makom Shevisah, it is not possible for the 'Techum itself' to choose any specific four Amos out of the eight because there is no criteria by which it should choose. Therefore, the Makom Shevisah automatically tries to take effect on all eight Amos. Moreover, when a person says "four *out of eight*," as opposed to "four," it is clear that he wanted *some* element of Shevisah to exist in *all* of the eight Amos. (It is not possible to split a Makom Shevisah into two non-contiguous areas.) Since a Makom Shevisah cannot take effect on four Amos after it has already taken effect on a different four Amos, it cannot take effect on eight Amos together at one time either.

In the case of Ma'aser, when one separates 20% as Ma'aser, he obviously did so because he wanted the Ma'aser to take effect on part of *all* 20% -- that is, half of each particle of grain. Since that *is* possible (i.e., it can take effect on non-contiguous grains), it does take effect.


QUESTION: Abaye says that if the area underneath the tree is less than 12 Amos, and one says that four of those Amos should be his Makom Shevisah, then one is Koneh Shevisah underneath the tree. The reason is because since there is one circle of four Amos diameter (i.e. in the center) that reaches into every other circle of four Amos diameter that can be drawn underneath the tree, and there is no possible contiguous four-Amos area which is not partially included in that center circle, it is considered to be a specific enough description of the area in order to be Koneh Shevisah.

Rav Huna brei d'Rav Yehoshua rejects this suggestion. It is irrelevant if there is one circle of four Amos that would reach into every other circle of four Amos. As long as it is not known where indeed he wanted *his* particular circle of 4 Amos to be, he should not be Koneh Shevisah anywhere underneath the tree! Therefore, Rav Huna brei d'Rav Yehoshua says that only if there is less than *8* Amos under the tree is he considered to have specified a clear Makom Shevisah, since it is known for sure that at least the middle Amah must be part of his actual Makom Shevisah.

Why indeed did Abaye think that one can be Koneh Shevisah even where there is so much uncertainty, and it is not known where even one Amah of his Shevisah actually is?

ANSWER: The RITVA answers that according to Abaye, since the center circle will definitely include part of any 4-Amah radius circle under the tree, we therefore *assume* that the center circle is indeed *exactly* where he wanted his Makom Shevisah to be.

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