Talmud - Eruvin 5a עירובין ה׳ א׳

And the one who said four handbreadths holds that the alleyway is considered as if it were sealed from the inside edge of the cross beam, and consequently it is prohibited to utilize the area beneath the cross beam. As the area beneath the cross beam is not part of the alleyway, a significant demarcation, i.e., one of four handbreadths, is required within the alleyway itself.

The Gemara rejects this explanation: No, everyone agrees that it is permitted to utilize the area beneath the cross beam, and they disagree with regard to this: This Master, Rav Yosef, holds that a cross beam functions in an alleyway as a conspicuous marker that demarcates the alleyway from the public domain, and consequently a mere handbreadth is sufficient, as even a handbreadth is sufficiently conspicuous. And this Master, Abaye, holds that a cross beam serves as a partition, and a partition is not effective for an area of less than four handbreadths. The principle that an outer edge descends and seals the alleyway does not apply if the beam is higher than twenty cubits. In order for it to be considered a partition, there must be at least four handbreadths that are less than twenty cubits beneath the cross beam.

The Gemara proposes an alternative explanation: And if you wish, say instead that everyone agrees that a cross beam serves as a conspicuous marker, and here they disagree with regard to the relationship between a conspicuous marker below, i.e., the raised area of the alleyway, and a conspicuous marker above, i.e., the cross beam. This Master, Rav Yosef, holds that we say that the halakha that governs the conspicuous marker below is like the halakha that applies to the conspicuous marker above, and one handbreadth suffices. And this Master, Abaye, holds that we do not say that the halakha that governs the conspicuous marker below is like the halakha that applies to the conspicuous marker above. The lower sign must be more prominent and extend four handbreadths.

The Gemara proposes yet another explanation of the amoraic dispute: And if you wish, say instead that everyone agrees that we say that fundamentally, the halakha that governs the conspicuous marker below is like the halakha that applies to the conspicuous marker above, and even a handbreadth should suffice. But here they disagree whether the Sages decreed that four handbreadths are necessary, lest people treading upon it will erode and diminish the raised area. Rav Yosef is not concerned that it will be diminished and therefore holds that a raised area of a handbreadth is sufficient, whereas Abaye is concerned that the raised area of a handbreadth will erode to less than a handbreadth, rendering it inconspicuous, and the alleyway will come to be utilized in a prohibited manner.

The Gemara considers a new case: If the cross beam spanning the entrance to an alleyway was less than ten handbreadths above the ground, and one hollowed out the ground under the cross beam in order to complete the distance from the ground to the cross beam to ten, how much must he hollow out? The Gemara is surprised by the question: How much must he hollow out? However much is necessary for it to increase the height to at least ten handbreadths. Rather, the question is as follows: How far must the hollowed-out area extend into the alleyway in order to render it permitted to carry throughout the alleyway? Rav Yosef said: Four handbreadths. Abaye said: Four cubits.

The Gemara suggests: Let us say that these amora’im disagree with regard to the ruling of Rabbi Ami and Rabbi Asi. As it was stated with regard to the following question: If the side wall of an alleyway was breached toward its entrance, i.e., close to where the alleyway opens into the public domain, what is the halakha? It was stated in the name of Rabbi Ami and Rabbi Asi: If an upright board four handbreadths wide remains of the original wall or is set up where the original wall had ended, the cross beam or side post at the entrance to the alleyway renders it permitted to carry in the alleyway even if there is a breach of up to ten cubits wide.

And if there is no upright board there, the following distinction applies: If the breach is less than three handbreadths, the cross beam or side post renders it permitted to carry in the alleyway, based on the principle of lavud. If the breach is three or more handbreadths, the cross beam or side post does not render it permitted to carry. The Gemara proposes that Rav Yosef, who says that the hollowed-out area need only extend four handbreadths, adopts the opinion of Rabbi Ami, whereas Abaye, who requires a hollowed-out area of four cubits, does not adopt the opinion of Rabbi Ami.

The Gemara rejects this argument: Abaye could have said to you that the two cases are not comparable: There, in Rav Ami’s case, we are dealing with the final stage of an alleyway, i.e., an alleyway that had at first been properly structured, and only later did it become breached. Here, we are dealing with the initial stage of an alleyway, i.e., an alleyway that from the very outset did not fulfill the necessary conditions. In this case: If there are four cubits in the hollowed-out area, yes, it is considered an alleyway, and if not, no, it is not considered an alleyway.

Abaye said: From where do I say that a length of at least four cubits is required? As it was taught in a baraita: An alleyway is permitted by means of a side post or cross beam only if it has both houses opening into courtyards and courtyards opening into it, as only in that case can it be called an alleyway.

And if the entire length of the alleyway is only four handbreadths, as is indicated by Rav Yosef’s opinion, how can you find this case? Under what circumstances is it possible for such a short alleyway to have courtyards opening into it? Even if there are only two such courtyards, the entrance to each is at least four handbreadths wide.

And if you say that the alleyway opens into the courtyards through its middle wall, i.e., the alleyway is only four handbreadths long but is wide enough to have two entrances opening into two courtyards, this is difficult. Didn’t Rav Naḥman say that we hold on the authority of tradition: Which is an alleyway that is permitted by a side post or a cross beam? Any alleyway whose length is greater than its width and has houses and courtyards opening into it. Accordingly, if the alleyway is only four handbreadths long, its width must be even less than that. Consequently, argues Abaye, a length of at least four cubits is required.

And Rav Yosef, how would he respond to this? Rav Yosef explains that the baraita is dealing with a case where the courtyards open into the alleyway at its corners. In this way it is possible to have two openings, each of which is at least four handbreadths wide, although the length of the alleyway itself is no greater than four handbreadths, as the four handbreadths of the openings to the courtyards are divided between the width and the length of the alleyway.

Abaye further said: From where do I say that a length of at least four cubits is required? As Rami bar Ḥama said that Rav Huna said: With regard to a side post that protrudes from the wall on the side of an alleyway into the opening of the alleyway, if its protrusion was less than four cubits, it is deemed a side post that renders it permitted to carry in the alleyway, and no other side post is required to render it permitted to carry in it. However, if it protruded four cubits, that section is deemed an alleyway, as though there were an additional alleyway within an alleyway, and another side post is required to render it permitted to carry there. This shows that anything less than four cubits does not have the status of an alleyway, which supports the position of Abaye.

The Gemara asks: And Rav Yosef, how would he respond to this? Rav Yosef distinguishes between the cases: With regard to removing its status as a side post, this status remains until there are four cubits in the length of the side post. However, in order to be deemed an independent alleyway, even with a wall of four handbreadths it is also considered an alleyway.

The Gemara examines Rami bar Ḥama’s statement cited in the course of the previous discussion. As to the matter itself: Rami bar Ḥama said that Rav Huna said: With regard to a side post that protrudes from the wall on the side of an alleyway into the entrance of the alleyway,

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Eruvin 5a examines the debate between Rav Yosef and Abaye over whether a crossbeam functions as a marker or partition in an alleyway.