Eruvin 48B

בשני בתים.

in two separate houses, and consequently the two outer courtyards do not join together and become as one.

כמאן? כבית שמאי, דתניא: חמשה שגבו את עירובן ונתנוהו בשני כלים, בית שמאי אומרים: אין עירובן עירוב. ובית הלל אומרים: עירובן עירוב.

The Talmud asks: In accordance with whose opinion did Rav Sheshet state that an eiruv placed in two houses, even within the same courtyard, does not join the houses together? He must have said this in accordance with the opinion of Beit Shammai, as it was taught in a baraita: With regard to 5 people who collected their eiruv and placed it in two separate utensils, even in a single house, Beit Shammai say: Their eiruv is not a valid eiruv, as the two parts of the eiruv have not been deposited in the same place, and Beit Hillel say: Their eiruv is a valid eiruv as long as the entire eiruv was deposited in a single domain.

אפילו תימא בית הלל, עד כאן לא קאמרי בית הלל התם ⁠— אלא בשני כלים בבית אחד, אבל בשני בתים, לא.

The Talmud rejects this argument: Even if you say that this is in accordance with the opinion of Beit Hillel, Beit Hillel may have stated their opinion only there, with regard to two utensils that are located in one house and consequently, they join together. However, if the two utensils are located in two separate houses, even Beit Hillel agree that the eiruv is not valid.

אמר ליה רב אחא בריה דרב אויא לרב אשי: לרב יהודה קשיא ולרב ששת קשיא. לרב יהודה קשיא דאמר: כגון שנתנה אמצעית עירובה בזו ועירובה בזו, וכיון דעירבה אמצעית בהדי חיצונה הויא ליה חדא, וכי הדרה וערבה בהדי אידך ⁠— שליחותה עבדה.

Rav Aḥa, son of Rav Avya, said to Rav Ashi: The explanation of Rav Yehuda is difficult and the explanation of Rav Sheshet is difficult. The explanation of Rav Yehuda is difficult, as he said that it is speaking about a case where the middle courtyard put its first eiruv in the one courtyard and its second eiruv in the other courtyard. However, once the middle courtyard establishes an eiruv with one of the outer ones, they are regarded as one, so that when it later establishes an eiruv with the other outer courtyard, it acts also on behalf of the first outer courtyard, as both of them are treated like a single courtyard.