Pi Tikra — Eruvin 90b

Pi Tikra — Eruvin 90b

תלמוד בבלי מסכת עירובין דף צ/ב

פי תקרה יורד וסותם

From The Contemporary Eruv:

In 1952, Rabbi Raphael Ber Weissmandel wrote a proposal to permit carrying on Shabbos in Brooklyn on the basis of the elevated train lines. His rationale, however, was not based on the principle of tzuras ha'pesach, but on that of “pi tikra yored v'sosem” (literally: the lip of a roof comes down and closes). The principle, as defined in the Shulchan Aruch (361:2) is that, when a roof is at least four tefachim by four tefachim and set atop two complete walls, we view the thickness of the roof as an imaginary wall for the remaining two sides.² Rabbi Moshe Feinstein disagreed with Rabbi Weissmandel's application of this principle to elevated train lines (Igros Moshe, Orach Chaim 1:138). Among his reasons was his observation that several Rishonim do not view the principle of pi tikra as creating walls, but as creating a defined area (underneath the ceiling) in which one is allowed to carry. Thus, perhaps one might be permitted to carry directly underneath the elevated tracks, but the tracks could still not serve to enclose the area that they enclose.

The Tikvas Zecharia (Rabbi Zecharia Rosenfeld, first Chief Rabbi of St. Louis, MO) notes that telegraph poles often support a thicket of wires at their tops. These wires are well within three tefachim of each other. Viewing them, halachically, as connected, allows one to consider the thicket as a roof. One could then apply the principle of pi tikra yored v’sosem to them. In practice, however, Rabbi Rosenfeld does not utilize this approach in sanctioning the use of the telegraph poles and wires as halachic walls, preferring instead the already accepted trend to view them as comprising tzuros ha'pesach. He does, however, propose that the presence of these “roofs” along the length of a street will diminish their potential to be regarded as a reshus ha'rabbim, since roofed over reshuyos ha'rabbim are automatically downgraded to carmelis status. - see Nesivos Shabbos 3:1 and note 6, where he considers (inconclusively) how much of a roof is necessary to negate a reshus ha'rabbim.