Eruvin 2 - Houses, courtyard, alley

The Talmud assumes the following organization of houses.

Several houses open into a courtyard, and several courtyards open into an alley. Usually the alley has one of its ends closed, so strictly speaking all of these areas are private domains, and one should be allowed to carry from any house to any house, in the courtyard and in the alley.

However, since these structures are similar to public areas, like a street, and since one can confuse the two and come to carry in the street, the Sages prohibited carrying between the houses through the courtyard and between the courtyard through the alley - unless some preparations have been made. A symbolic fourth wall has to be created, even if it just a beam across, and common food has to be stored, making all residents as if one family.

A beam that is placed across the entrance into an alley must not be higher than twenty amot (about 40 feet). If it is higher, it must be placed lower. The Talmud immediately asks: we will learn that a sukkah must not be higher than twenty amot, and if it is higher than that, it is invalid. Why "invalid" for sukkah but "placed lower" for an alley? The answer: since the sukkah requirement is dictated by the Torah, then the Sages just tell you the law, "invalid." The beam over an alley, however, is dictated by the Sages themselves, and as they explain it, they can also tell you how to fix it.

Or, if you want, I can give you another explanation. Since the laws of the sukkah are numerous (shade, sun, walls, etc.) it is easier to just say "invalid" and let you find a way to fix it. The laws of an alley are relatively simpler, and the Sages can start teaching them right away by saying "place it lower."


Art: Gillis van Tilborgh - An Elegant Company Eating, Drinking And Smoking In The Courtyard