Eruvin 90

Invisible boundaries.

In yesterday’s mishnah, Rabbi Meir and the rabbis disagreed about whether rooftops form individual domains. The rabbis held that each home’s rooftop is its own domain and without an eruv one cannot carry an item across to the next rooftop; Rabbi Meir held that continuous rooftops count as one domain, as long as the rooftops are contiguous and not of wildly differing heights.

Today, we pick up in the middle of an early amoraic conversation between two famous interlocutors, Rav and Shmuel, who offer different interpretations of the rabbis’ position (that each rooftop is a separate domain). Rav thinks that when the roofs are interconnected with no visual marker one can only carry for the minimum distance of four cubits because one might accidentally walk over the boundary without noticing (carrying four cubits in the public domain is permissible, but no more). For Rav, a visible boundary is a must, though this results in a very restrictive reading of the mishnah. Shmuel, on the other hand, says that one can simply imagine the boundary between dwellings extending upward onto the roofscape, allowing a person to walk and carry an object freely on the roof of any particular dwelling as long as they are careful to remain over that single dwelling. Shmuel’s interpretation seems more in line with the intended meaning of the mishnah, and it is also more lenient.

Rav and Shmuel agree about one case, however: if a small house abuts a larger one, even the more stringent Rav (who normally holds you can only carry four cubits on a rooftop) agrees that you can extend the boundaries from the houses onto the roof above because you can clearly see where the small house ends and the bigger house begins. That is, he is willing to imagine a boundary if there are enough visual cues to draw it accurately.

Back in Tractate Berakhot we noted that discussions between the interlocutors Hillel and Shammai nearly always followed a predictable pattern: Shammai was more stringent, Hillel more lenient. But as the discussion between Rav and Shmuel continues on today’s page, we discover that these two are more committed to certain legal principles than to stringency or leniency.

Now the Gemara brings a related case where suddenly Shmuel is the more stringent of the two:

It was further stated that they disagreed with regard to a large ship.

Rav said: It is permitted to move an object throughout the entire ship, as it is all one domain.

Shmuel said: One may move an object in it only four cubits.

Rav said: It is permitted to move an object throughout the boat, as there are partitions (walls that separate the ship from the water). 

Shmuel said: One may move an object in it only within four cubits, as the partitions of the ship are not considered full-fledged partitions; they are erected only to keep water out, not to render it a residence.

The walls of a ship, Shmuel says, do not create a residence and so one may only carry a maximum of four cubits on a boat during Shabbat. In this case, Rav allows a person to carry freely around the ship because the edge of the domain is very clearly demarcated; he is now far more lenient.

Down today’s page, these two sages continue their debate in the case of a portico. Like Shmuel’s stance on the boat, he is unwilling to “draw” an invisible boundary line when it is not a living space. Rav is also consistent with his previous opinion — he is willing to complete a partial barrier of the portico because there is a visible starting point for the invisible line.

Rav who appeared stringent becomes the lenient opinion and Shmuel switches from lenient to stringent ruling — yet, notably, they both remain consistent with their principles.

Read all of Eruvin 90 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on November 7th, 2020. If you are interested in receiving the newsletter, sign up here.

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