Mishneh Torah, Sabbath 17

Sugya Map

• Issue: The legal status of a mavoi (lane) and the mechanism required to permit carrying within it on Shabbat.
• Nafka Mina: Whether a mavoi with three walls is a carmelit (Rambam) or a reshoot hayachid (Rashi/Tosafot) mi-d'oraita.
• Primary Sources: Eruvin 11b, Eruvin 12a, Mishneh Torah, Sabbath 17.

Text Snapshot

Rambam states: "A lane with three walls is called a closed lane... According to Torah law, one is permitted to carry [within an area enclosed] by three partitions. [The requirement to enclose the] fourth side is Rabbinic" (Mishneh Torah, Sabbath 17:1).

Note the nuance: Rambam categorizes a three-walled enclosure as a carmelit by default, rendering it a makom patur (exempt space) mi-d'oraita. This contrasts with the classic view of many Rishonim (e.g., Tosafot, Eruvin 12a s.v. "mavo'i") who argue it is reshoot hayachid by Torah law.

Readings

• Rambam: The lechi or korah are not "walls" in the physical sense, but Rabbinic "distinctions" (haker) that lift the Rabbinic prohibition, as the area remains a makom patur mi-d'oraita.
• Rashi/Tosafot: They maintain that three walls suffice for reshoot hayachid mi-d'oraita. Thus, the lechi or korah serves to complete the "enclosure," theoretically turning the area into a full reshoot hayachid.

Friction

Kushya: If the lechi or korah is merely a Rabbinic "distinction" for a carmelit, why do we treat them with such geometric rigor (e.g., width of a handbreadth for a korah)? Terutz: As the Maggid Mishneh notes, the Rabbinic enactment was modeled after the requirements of a reshoot hayachid. The precision is not because the lechi is a wall, but because the Rabbis required the haker to mimic the structural integrity of a legal partition to effectively distance the space from the reshoot harabim.

Intertext

The dispute mirrors the broader conflict regarding the status of a carmelit vs. reshoot hayachid. See Shulchan Aruch, Orach Chayim 363:1, where the Be'ur Halachah highlights this exact tension between the Rambam's makom patur approach and the more standard reshoot hayachid approach.

Psak/Practice

While modern eruvin rely on the tzurat hapesach (frame of an entrance), the Rambam’s heuristic remains vital: the eruv functions as a legal signifier that differentiates the space. In practice, we follow the stringencies of both: we ensure the eruv is structurally sound as if it were a reshoot hayachid, while acknowledging the Rabbinic nature of the leniency.

Takeaway

The lechi or korah is not a physical wall, but a "conceptual boundary"—a legal mnemonic that separates our private Shabbat space from the public domain.