Navigating the Talmud’s Alleys
The range of problems and the variety of answers in the study of Oral Law lead to new pathways of reasoning
The Talmud gives two complementary reasons for the 20-amot rule, one theoretical and one practical. The theoretical reason goes back to the Temple in Jerusalem, where the entrance to the sanctuary was 20 amot high. This way of connecting Shabbat practice with the Temple reminded me of how, in Tractate Shabbat, the 39 forbidden labors or melachot were derived from the construction of the Tabernacle. Indeed, the Gemara spends some time arguing that the Tabernacle, which the Israelites built in the desert, and the Temple, which Solomon built in Jerusalem, are legally and scripturally connected, so that what applies to one also applies to the other.
Pragmatically, too, it’s important for the crossbeam not to be more than 20 amot high. This is because the function of the crossbeam is to remind people that they are passing out of a private domain, the mavoi, and into a public one, the street; and if it is too high up, passerby may not notice it. In Eruvin 3a, the rabbis draw an analogy with the succah, where the same height limitation applies. In a succah, the covering or s’chach may not be more than 20 amot from the ground, because the whole point of the succah is to give the feeling of being in an enclosed structure. If the roof is too high, the succah will fail in this purpose. By this logic, however, a crossbeam can be higher than 20 amot if it has a “prominence” (amaltra)—that is, some feature that makes it especially conspicuous. Examples of such features include “nests”—carved cornices resembling birds’ nests—and cedar poles.
What do you do if your crossbeam happens to be more than 20 amot high? You could lower it, of course; but as the rabbis point out, with typical thoroughness, you could also raise the ground under it. (This would not have been too hard to do in a place where the streets were made of dirt and could be dug up at will.) This brings up the question of how deep a raised platform one has to build under the crossbeam, that is, how far back into the mavoi it must extend. Rav Yosef holds that one tefach is enough—that is, about three inches. Abaye, on the other hand, requires four tefachim, about a foot. The difference, the Gemara explains, is that Yosef conceives of the crossbeam as just a reminder, while Abaye imagines it as a full partition. It is a good example of how, in the Talmud, what seem like trivial technical debates—a matter of a few inches—rest on deeper conceptual disagreements.
The rabbis go on to consider every possible permutation of alleyways and entrances. What if you have an L-shaped alley, which is open to the street at both ends: Does this constitute one open alley or two closed ones put together? What if the walls of a mavoi have crumbled so there’s a breach in them—how big an opening is required before the wall is considered to be legally void? What if an alley is bounded at one end by the sea or by a garbage dump, features that are not permanent and may change their shape?
In every imaginable case, the Talmud offers not just one answer, but a range of answers from different authorities. The variety is overwhelming, and I found it a struggle to keep all the different cases clear in my mind. Simply by thinking about the range of problems that might come up in everyday life, the Talmud demands that the student hone his powers of visualization and geometrical reasoning, as well as his powers of logical deduction. I’m beginning to understand how studying the Talmud alone constituted a whole education for generations of young Jews.
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