Eiruvin 70 - 76
One Man's Family
An eruv chatzeros is required in order to permit carrying on Shabbos from a house to the courtyard when there are a number of houses of individual owners opening to a common courtyard. But what if all the houses are occupied by members of the same family?
The mishna informs us that if all the houses are occupied by different sons of the same man who eat and sleep in those houses then no eruv is required, provided all the sons receive their allowance for food from their father. This common dependence forms them into a single unit for which no eruv is necessary.
The gemara extends this rule to the wives (when polygamy was still permissible) or the servants who sleep and eat in their individual houses but rely on the head of the house for their support. A question is raised in regard to Torah students who sleep and eat in their own houses but rely on their teacher for their support. The issue is resolved by quoting the historical precedents of the Sage Rav when he studied by his teacher Rabbi Chiya and that of Rabbi Chiya himself when he studied by the Sage Rebbi. In both cases it was ruled that no eruv was necessary because the students depended on the teacher for their food.
Why did the gemara even assume that there might be a difference between the relationship of student-teacher and that of father-son, husband-wife and master-servant?
There are two dimensions to the formation of a single unit from disparate elements. One is the relationship of the dependents to the source of their support. The other is the relationship of the dependents to each other.
In the case of sons and a father or wives and a husband, there are familial and legal bonds connecting each of the dependents to the head of the family as well as to each other, which are forged into a single unit by the economic factor of dependence. Even in the case of servants and their master there is a relationship of labor obligations which serves as the link connecting servant and master and servants to each other. When it comes to a student, however, there is neither family bond nor any legal obligation to form a link to the teacher or to each other. This gave rise to the consideration that they cannot be formed into a single unit through common dependence alone.
The historical precedents cited teach us that there is such a strong bond between a Torah teacher and his students and the students with one another that they too can be formed into a single family unit.
What Makes a Window
When can the residents of two adjoining courtyards make a joint eruv to permit carrying from one to the other?
If there is a passageway in the wall between the two, there is no question that such an arrangement can be made. But if there is only a window connecting the two and the residents of the courtyards wish to pass objects through that window, the window must be at least four handbreadths by four handbreadths in size in order to connect them.
What is the reason for these particular dimensions?
One possibility is that they are determined by the rule of lavud which states that any separation less than a certain minimum is considered as being nonexistent. This rule, which is a halacha leMoshe miSinai (a law received by Moshe Rabbeinu at Mount Sinai but not recorded in the written Torah) is applied in many places throughout the Talmud. It appeared in our own Mesechta (Eruvin 9a) in regard to a korah crossbeam placed at the entry to a mavoi street which did not quite reach all the way to the walls on which it was supposed to rest.
But if lavud is the issue, then we must conclude that our mishna beginning the seventh perek is in accordance with the opinion of Rabbi Shimon ben Gamliel, that any separation less than four handbreaths is considered as nonexistent. The majority opinion of the Sages, however, is that lavud applies only if the separation is less than three handbreaths.
The gemara rejects this apparent support for the minority opinion. Our mishna is indeed consistent with the majority view that lavud is inapplicable once there is a separation of three handbreadths or more. But even if such a separation exists, we cannot consider the two courtyards as linked because anything less than four by four cannot qualify as a connecting passageway.