Eruvin 9 – A crossbeam on two pegs

If one did not put his crossbeam as it he should, on the two walls where the alley goes into the street, but instead he placed it a little into the street, supported by two pegs, what is the law? Does the beam help to permit carrying on Shabbat in the alley or it does not?

Rav Chisda answered: “The one who permits – forbids, and the one who forbids – permits.” He meant as follows. Had the beam been placed normally, the one who permits carrying directly under the beam does so because he considers the outer edge of the beam as if doing down and separating the alley from the street. Accordingly, when the beam is too far from the alley, it does not help, and carrying in the alley is forbidden.

By contrast, one who usually forbids carrying under the beam says so because he considers the inner edge of the beam as if going down and separating the alley. Therefore, the beam on two pegs, even though it is in the street, has its inner edge is right next to the alley, so it does separate the alley from the street, which means that carrying there is allowed.

Nice as this logic was, Rava disagreed with it, saying simply that the beam should be right over the alley. Since this is not true in our case, a beam on the pegs is invalid, and so is the law.

Art: Edwin Deakin - St Louis Alley