Siman - Eruvin Daf 50
- Two versions of how Rabbah explained Rav’s position
On Daf 49b Rav stated that one who did not specify his makom shevisa under a tree not only does not attain a makom shevisa there but also does not have a makom shevisa in his current location. There are two versions of how Rabbah explained Rav’s reasoning that one does not attain a makom shevisa under the tree.
The first version is, משום דלא מסיים אתריה – because his four-amah area is not defined. Rashi explains that since it is not defined, he does not acquire anything. The second version is משום דקסבר כל שאינו בזה אחר זה – because he holds that whichever legal situations cannot take effect consecutively, אפילו בבת אחת אינו – cannot take effect simultaneously. Rashi explains that the halachah allows a person to only establish one dalet amos area as his residence, and once he does, he can no longer establish a second residence. He can therefore not designate more than one residence simultaneously, and if he does, none of them are valid. In this case, since the area beneath the tree covers several four-amah areas, and he is not specifying which four-amah is his residence, it is as if he is designating them all simultaneously, which does not work.
- How wide an area under the tree
Abaye said regarding Rav’s ruling, לא שנו אלא באילן שתחתיו שתים עשרה אמה – it was only taught regarding a tree that has an area of twelve amos beneath it, but in the case of a tree that does not have twelve amos beneath it, הרי מקצת ביתו ניכר – a portion of his residence is recognizable. Rashi explains that since the tree’s width is less than twelve amos, the middle four amos necessarily include a section of the four amos areas on either side of the tree. Regardless of whether his dalet amos is the middle section or one of the side sections, at least a portion of his residence is in the middle four amos, and Abaye considers this enough to establish a residence for him.
Rav Huna brei d’Rav Yehoshua objected, saying there is no basis that the middle four amos are his residence, and knowing that part of his residence falls somewhere within them is not sufficient to make his residence defined. Therefore, he taught that Rav’s ruling applies in a case where the tree has eight amos beneath it, but if it has just seven amos, הרי מקצת ביתו ניכר – a portion of his residence is recognizable beneath the tree. In this case, any division into four-amah units necessitates having the units overlap, at least partially.
- Placing two eruvin in opposite directions
A Baraisa is brought to support Shmuel’s position (see 49b), that stated that if one erred and placed an eruv in both directions, believing that an eruv may be established in two directions, or if he said to his servants, “Go and establish an eruv for me,” and one of them placed an eruv for him in the north and the other placed one in the south, he may travel to the north only as far as his eruv to the south allows, and he may travel to the south only as far the as the eruv in the north allows, and if the two established techum boundaries do not overlap, but have him at the center point between them, he may not move from his place. The Gemara asks if this is a תיוובתא on Rav and answers, רב תנא הוא ופליג. Rav is a Tanna and he is allowed to disagree with a Baraisa.
