More Discussions for this daf
1. Using Bereirah to select an unspecified place of an Eruv 2. Techumin 3. Beraita at bottom of Amud B of Daf 50
DAF DISCUSSIONS - ERUVIN 50

Michael Winoker asked:

Why is the principle of Bererah not used to applied to resolve the difficulty according to Rav that kol sheayno bazeh achar zeh afilu bevat achat ayno? That is, if one can use bererah to select one of two eruvim in opposite directions, why can it not be used to selct the exact place under the tree?

The Kollel replies:

You've raised an interesting point.

The difference between the case of an Eruv under a tree and the case of two Eruvin in opposite directions is that in the latter case, the person states explicitly that he wants only one of the Eruvin to be effective (the one on whichever side the Chacham comes, which will become known the next day). In our case, though, he did not state that the Eruv should take effect in "four of the eight Amos" beneath the tree, and therefore it is as if he said that the Eruv should take effect in all eight Amos.

In fact, the Gemara says that if he specified that the Eruv should take effect in "four out of eight" Amos, then the Eruv is valid. Perhaps the reason is as you wrote, because of Bereirah. (There is, though, one opinion in our Sugya that holds that even in such a case the Eruv is not valid, and does not explain his reasoning; perhaps his reasoning is that he holds Ein Bereirah even in Dinim d'Rabanan.)

Be well, Mordecai