GEMARA: Rav Yehuda said that Shmuel said: If one established his Shabbat residence in a desolate city whose walls are still standing, according to the Rabbis he may walk through all of it as though it were four cubits, and he may walk an additional two thousand cubits beyond it. If, however, he merely placed his eiruv in a desolate city, he has only two thousand cubits from the place of his eiruv. The Rabbis distinguish between one who establishes his Shabbat residence by actually being present in that location at the onset of Shabbat and one who does so by placing his eiruv there before Shabbat. Rabbi Elazar says: Whether he established his Shabbat residence through his physical presence or he merely placed his eiruv there, he may walk through all of it and another two thousand cubits beyond it.

The Gemara raises an objection based upon the mishna. Rabbi Akiva said to the Rabbis: Do you not concede to me that one who places his eiruv in a cave has only two thousand cubits from the place of his eiruv? They said to him: When does this apply? When the cave has no residents. Consequently, when it has no residents the Rabbis concede to Rabbi Akiva that one has only two thousand cubits from the place of his eiruv. This contradicts Rabbi Elazar’s assertion that, according to the Rabbis, even if one places his eiruv in the abandoned city, he may walk through all of it and another two thousand cubits beyond it.

The Gemara responds: What is the meaning of the qualification that it has no residents? It means that the place is not fit for residence. If, however, the city is suitable for habitation, it is considered like four cubits even if it is currently uninhabited.

Come and hear another difficulty from the following baraita: If one established his Shabbat residence through his physical presence in a city, even if it is as large as Antioch, or in a cave, even if it is particularly large, like the Cave of Zedekiah, king of Judah, he may walk through all of it and another two thousand cubits beyond it. The baraita teaches the case of a city that is similar to that of a cave: Just as a cave is presumably desolate, i.e., uninhabited, so too the city must be one that is desolate. And only in the case where he established his Shabbat residence through his physical presence would yes, this halakha apply; but if he merely placed his eiruv there, no, he may not measure his two thousand cubits from the edge of the city.

The Gemara continues clarifying the baraita: In accordance with whose opinion is this baraita? If you say it is in accordance with the opinion of Rabbi Akiva, why did the baraita specifically teach the case of a desolate city? Even if it was inhabited, the same halakha should also apply, as Rabbi Akiva holds that even if one placed his eiruv in an inhabited city, he has only two thousand cubits from the place of his eiruv. Rather, is it not in accordance with the opinion of the Rabbis? And nonetheless, the reason is that one established his Shabbat residence through his physical presence. In such a case, yes, one may walk through the entire city and another two thousand cubits beyond it. But if one merely placed his eiruv there, he would not be permitted to walk more than two thousand cubits from his eiruv, which would contradict the opinion of Rabbi Elazar.

The Gemara rejects this argument and argues that the initial inference was incorrect. Do not say that the baraita is referring to a city that is similar to a cave. Rather, say that it is referring to a cave that is similar to a city: Just as the city is presumably inhabited, so too the cave must be one that is inhabited. The baraita is then in accordance with the opinion of Rabbi Akiva, who said that if one merely places his eiruv in the cave, he has only two thousand cubits from the place of his eiruv. However, if one established his Shabbat residence there through his physical presence, even Rabbi Akiva concedes that the entire cave is considered as though it were four cubits, and he may walk two thousand cubits beyond the cave.

The Gemara asks: Doesn’t the baraita teach that this halakha applies even to a cave like the Cave of Zedekiah, which was uninhabited? The Gemara answers: The baraita is referring to a cave that is like the Cave of Zedekiah in one respect and not like the Cave of Zedekiah in other respects. It is like the Cave of Zedekiah in that the cave is as large as that one. And it is not exactly like the Cave of Zedekiah, as there, with regard to Zedekiah’s cave, it was desolate, and here the baraita is referring to a cave that is inhabited.

The Gemara relates that Mar Yehuda once found the residents of Mavrakhta placing their eiruvin in the synagogue of Beit Agovar. He said to them: Place your eiruv farther into the synagogue, so that more will be permitted to you, as the Shabbat limit is measured from the spot where the eiruv is deposited. Mar Yehuda holds that even when an eiruv is placed in an inhabited city, the two thousand cubits are measured from the location of the eiruv rather than from the edge of the city.

Rava said to him: Argumentative one! With regard to the halakhot of eiruv, nobody is concerned about this opinion of Rabbi Akiva, as the halakha is in accordance with the opinion of the Rabbis. Consequently, no matter where one places his eiruv in a city, the entire city is considered as though it were four cubits, and he is permitted to walk two thousand cubits beyond the edge of the city.

MISHNA: One who resides with a gentile in the same courtyard, or one who lives in the same courtyard with one who does not accept the principle of eiruv, even though he is not a gentile, such as a Samaritan [Kuti], this person renders it prohibited for him to carry from his own house into the courtyard or from the courtyard into his house, unless he rents this person’s rights in the courtyard, as will be explained below.

Rabbi Eliezer ben Ya’akov says: Actually, the gentile does not render it prohibited for one to carry, unless there are two Jews living in the same courtyard who themselves would prohibit one another from carrying if there were no eiruv. In such a case, the presence of the gentile renders the eiruv ineffective. However, if only one Jew lives there, the gentile does not render it prohibited for him to carry in the courtyard.

Rabban Gamliel said: There was an incident involving a certain Sadducee who lived with us in the same alleyway in Jerusalem, who renounced his rights to the alleyway before Shabbat. And Father said to us: Hurry and take out your utensils to the alleyway to establish possession of it, before he changes his mind and takes out his own utensils so as to reclaim his rights, in which case he would render it prohibited for you to use the entire alleyway.

Rabbi Yehuda says: Rabban Gamliel’s father spoke to them with a different formulation, saying: Hurry and do whatever you must do in the alleyway prior to Shabbat, before he takes out his utensils and renders it prohibited for you to use the alleyway. In other words, you may not bring out utensils to the alleyway at all on Shabbat, as the institution of an eiruv cannot be used in the neighborhood of a Sadducee. This is because, even if he renounced his rights to the alleyway, he can always retract and reclaim them.