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Peninei Halakha > Shabbat > 29 – Eruvin > 01. Transforming a Public Domain

01. Transforming a Public Domain

As we learned in chapter 21, one may transport items on Shabbat within a private domain (reshut ha-yaĥid) but not more than four amot within a public domain (reshut ha-rabim) and not from a public to a private domain and vice versa.

An eruv, however, transforms a reshut ha-rabim into a reshut ha-yaĥid, thus allowing people to transport items within that area without limit, as well as to transport items from homes and yards into that area, and vice versa.

An eruv has two components, one pertaining to the area that will be transformed into a private domain, and the other relating to the people who will live within the eruv’s boundaries. In order to define the area as a single private domain, it must be enclosed by a fence. However, this is not enough. The people who live within the area must also establish a partnership with one another. This is done by means of two meals worth of food that is owned collectively by everyone and from which anyone may partake. This communal food is called an eruv (literally “merging”) because it merges or joins together all the homes and yards, turning them into a single private domain. Nevertheless, it has become commonplace to call the enclosure itself an eruv as well, and we follow this convention.

As we learned (21:2-3), there is a difference between a reshut ha-rabim by Torah law and a semipublic domain (karmelit), which is treated as a reshut ha-rabim by rabbinic law. In order to permit carrying in a reshut ha-rabim by Torah law, the area must be enclosed by a wall or fence at least ten tefaĥim high (approximately one meter),[1] and the gates that people use to enter the enclosure must be locked at night (SA 364:2).

However, a karmelit, considered a public domain on the rabbinic level, need not be enclosed by an actual fence. Rather, it is sufficient to surround it with tzurot ha-petaĥ (defined in the following section) to transform it into a reshut ha-yaĥid (SA 362:10-11).

[1]. A tefaĥ, according to R. Ĥayim Naeh, is eight cm. Ten tefaĥim, then, is 80 cm. He bases his calculations on Rambam’s opinion regarding the size of a dirhem (a unit of mass derived from the Greek drachma coin). However, it has since been ascertained that a dirhem at the time of Rambam was more than ten percent smaller in volume than the Turkish dirhem with which R. Naeh was familiar. This means that R. Naeh’s shi’ur is too large. Using the corrected measurements, a tefaĥ is 7.6 cm and ten tefaĥim is 76 cm. Ĥazon Ish, basing himself on Noda Bi-Yehuda, maintains that a tefaĥ is 9.6 cm. The law accords with Rambam, whose opinion is accepted by the vast majority of poskim, taking into account the current knowledge about the size of the dirhem. Nevertheless, for two generations, people have grown accustomed to relying on R. Naeh’s shi’ur. Additionally, some follow the stringent opinion of Ĥazon Ish. It would seem reasonable le-khatĥila to follow Ĥazon Ish when building an eruv (whether enclosed by a fence or tzurot ha-petaĥ), since sometimes the wire droops. When that happens, if the eruv was constructed based on a small shi’ur, its validity is uncertain. By following Ĥazon Ish, we avoid this problem. In addition, an eruv is meant to serve the entire community. Le-khatĥila, when acting on behalf of the entire community, it is more important than usual to try to meet the requirements of all the different opinions. In light of all this, I write generally that ten tefaĥim is approximately one meter (following Ĥazon Ish), even though technically one could follow the smaller, updated shi’ur. When there is a gap of ten amot, which can disqualify the eruv, one should be stringent and use the smaller, updated shi’ur of 4.56 m.

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