Today’s daf (Eruvin 6a-b) is one of the most fundamental throughout Massechet Eruvin in outlining the principles and details necessary for the contemporary eruvin that surround various cities around the world:
“Our Rabbis taught [in a Beraita]: How do we create an eruv [and therefore halachically privatise] a street of the public domain (רשות הרבים)? [The Tana Kamma teaches that] we construct a form of a doorway (צורת הפתח) from here [on one side of the public domain], and [we construct either] a sidepost (לחי) or a crossbeam (קורה) from here [on the other side of the public domain]. Hananya [disagrees] and says: [This question has previously been addressed by Beit Shammai and Beit Hillel]. Beit Shammai say: We construct a [physical] door from here [on one side of the public domain], and a door from here [on the other side of the public domain], and when one exits or enters, the door must be closed. [But] Beit Hillel says: We construct a [physical] door from here [on one side of the public domain], and a a sidepost (לחי) or a crossbeam (קורה) from here [on the other side of the public domain].”
Fundamentally, what this question raises is whether an eruv that is constructed in order to enable carrying in a public domain by halachically privatising a public domain must, at least in some parts of it, employ physical walls/doors (which, it should be noted, seems to be supported by the statement in Eruvin 6b that ‘were it not that the doors of [Jerusalem] were closed at night, one would have been liable for carrying [in Jerusalem, since, without those physical doors, would have been regarded as] a public domain’), or whether, as suggested by a variety of rabbinic teachings found in our daf and elsewhere, it may solely rely on the halachic partitions of ‘a form of a doorway’ (צורת הפתח), a sidepost (לחי), or a crossbeam (קורה), and as the Gemara (Eruvin 6b) notes, this is a matter of dispute. However, a no less critical question to consider is what exactly is a public domain (רשות הרבים).
The most stringent definition of a public domain is presented by the Rambam (Shabbat 14:1) who categorises a public domain as: ‘deserts, forests, marketplaces, and any road that opens into them, presuming that the road is [at least] 16 amot (approx. 8 metres) wide and is not covered’. According to the Rambam, a public domain is fundamentally defined by its ‘openness’, and thus only cities like Jerusalem that could, in some way, be physically ‘closed off’ can be transformed into a halachically private space. Significantly, this position is presented first by Rabbi Yosef Karo in his Shulchan Aruch (Orach Chaim 345:7).
However, other authorities disagree. Specifically, Rashi (in his commentary to Eruvin 6a DH Reshut HaRabim and Eruvin 6b DH Yerushalayim), as well as the BeHag (cited by Tosfot to Eruvin 6a DH Keitzad), explain that a public domain is an unwalled area with roads that are [at least] 16 amot (approx. 8 metres) wide and with foot traffic of at least 600,000 people. Such a definition practically means that almost no neighbourhood can be defined as a public domain. Significantly, this position is presented by Rabbi Yosef Karo in his Shulchan Aruch (Orach Chaim 345:7) as a second יש אומרים (literally ‘some people say’) opinion.
Over the centuries, many opinions have been offered concerning both these debates of what constitutes a public domain, as well as the necessary qualities of an eruv to halachically privatise a public domain.
Naturally, on the basis of some of the above-mentioned positions, there are those who have questioned the halachic possibility of creating eruvin in modern metropolitan areas. At the same time, there are others who have emphasised how the establishment of Eruvin in Jewish neighbourhoods is an essential halachic duty to halachically enable a range of activities on Shabbat.
Ultimately, notwithstanding the rationale for the stricter position, it is essential to acknowledge the halachic validity of both positions and thus, as Rabbi Yisrael Meir Kagan writes in his Mishna Berura (Orach Chaim 364 note 8), even those who adopt a stricter position ‘should not raise objections to others who have accustomed themselves to follow the more lenient position which employs [the halachic boundary of] a form of a doorway (צורת הפתח) – especially since it has been the consistent custom [of communities] to follow those authorities who are lenient [in this matter]’.