How does an eruv hatzairot work? TB Eruvin 49

Yesterday we learned the biblical source why a person can’t walk more than four amot outside his tekhum. That’s why the rabbis instituted the eruv tekhumim to extend the distance another 2000 amot in one direction. On TB Eruvin 49 we learn how an eruv hatzairot (ערוב חצרות) works. Just to refresh your memory, back in talmudic times several houses open up to one courtyard, hatzair-חצר. For people of the different houses to carry from their house to the courtyard and back, they all had to contribute to the eruv hazairot. This type of eruv unifies the courtyard. Of course, there’s a disagreement between Shmuel who believes that the underlying principle is one of an acquisition, קנין and Rabba who believes that the underlying principle is one of residence, דירה.

“Shmuel said: An eiruv that is deposited in a house is effective due to the principle of acquisition, as each person who contributes a portion of food acquires the right to a certain use of the residence and is considered one of its residents.

“And if you say: Why then can one not acquire this right through payment of a coin such as a ma’a, but rather only through bread? It is because a ma’a is not always available on Shabbat eve, as many people spend all of their available money for the necessities of Shabbat, and it is difficult to find money available at that hour.

“The Gemara asks: If so, according to Shmuel’s opinion, in a case where he established an eiruv with money, it should nonetheless acquire, i.e., be valid. According to his opinion, there is no fundamental reason to invalidate the acquisition of rights in the residence through the payment of money, yet there is no indication that this position is valid.

“The Gemara answers: Even Shmuel did not permit one to establish an eiruv with money, due to a decree lest people say that a ma’a is essential, and sometimes a ma’a will not be available, and they will not come to prepare an eiruv with bread, and the halakhic category of eiruv will be forgotten.

 “Rabba disagreed with Shmuel and said: An eiruv is effective due to the principle of residence. Each person who contributes a portion of food is considered as if he resides, for that Shabbat, in the residence in which the food is deposited.” (Sefaria.org translation)

The Gemara delineates three practical differences between these two approaches. I’ll just share the last one because I think it is the most important. “And there is another practical difference between them with regard to the question whether a minor may collect the eiruv from the residents of the courtyard and deposit it in one of the houses. According to Shmuel’s opinion, this would not be a valid eiruv, for a minor cannot serve as an agent to effect acquisition, whereas according to Rabba’s opinion, the eiruv is valid, as the food itself establishes the common residence for all the residents.” (Sefaria.org translation)

The halakha follows Rabba’s position; consequently, a person may use a minor as an agent to collect the bread for the eruv hatzairot (ערוב חצרות) and the contribution of bread can be worth less than a prutah, but one may not use an utensil. Shulkhan Arukh, 366:3