it is obvious, for the private domain ascends to the sky, and just as it ascends upward, so too, it descends downward to the bottom of the pit, even if it is more than ten handbreadths deep. Rather, we must say that the pit is situated in the public domain.

The Gemara now clarifies: Where did one intend to establish his Shabbat residence? If he intended to establish his residence above the pit in the public domain, this is a case where he is in one place and his eiruv is in another place, i.e., in a private domain, and therefore his eiruv is not valid. Alternatively, if one intended to establish his Shabbat residence below, in the pit, it is also obvious, as he and his eiruv are in one place.

The Gemara answers: This ruling is necessary only in a case where the pit is situated in a karmelit, and he intended to establish his Shabbat residence above the pit in the karmelit. And with regard to the question of how this eiruv can be valid, as one cannot bring the eiruv from the pit to the karmelit, the answer is that the mishna was taught in accordance with the opinion of Rabbi Yehuda HaNasi, who said: With regard to anything that is prohibited on Shabbat due to rabbinic decree [shevut], they did not issue the decree to apply during twilight. Since carrying from the pit to the karmelit is only prohibited as a shevut, a person may carry from the pit to the karmelit during twilight, the time when the eiruv establishes one’s Shabbat residence.

MISHNA: If one placed his eiruv on top of a reed or on top of a pole [kundas], when the reed or pole is detached from its original place and stuck into the ground, even if it is a hundred cubits high, it is a valid eiruv, as one can remove the reed or pole from the ground and take his eiruv.

GEMARA: Rav Adda bar Mattana raised a contradiction before Rava concerning two tannaitic rulings: The mishna states that if the reed was detached from its place of growth and then stuck into the ground, yes, the eiruv is valid. That indicates that if it was not detached and then stuck back into the ground, no, the eiruv is not valid. In accordance with whose opinion is this mishna? It is in accordance with the opinion of the Rabbis, who say: Anything that is prohibited on Shabbat due to rabbinic decree [shevut], such as using a tree on Shabbat, they issued the decree to apply even during twilight. Therefore, if the eiruv was on top of a reed that was still attached to the ground in its original place of growth, since it is prohibited by rabbinic decree to make use of trees on Shabbat, one cannot remove the eiruv from its place at the time that he must establish his Shabbat residence, and therefore his eiruv is invalid. But didn’t you say that the first clause, i.e., the previous mishna, is in accordance with the opinion of Rabbi Yehuda HaNasi? How can you say that the first clause is in accordance with the opinion of Rabbi Yehuda HaNasi and the latter clause is in accordance with the opinion of the Rabbis?

Rava said to Rav Adda: Rami bar Ḥama already raised this contradiction before Rav Ḥisda, and Rav Ḥisda answered him: Indeed, the first clause is in accordance with the opinion of Rabbi Yehuda HaNasi, and the latter clause is in accordance with the opinion of the Rabbis.

Ravina said: You can, in fact, say that it is all Rabbi Yehuda HaNasi, and the latter clause, i.e., the mishna that insists that the reed be detached and inserted, is not based upon the prohibition of utilizing trees on Shabbat. Rather, in that case there is a unique decree lest he break it off from the ground if the reed is relatively soft. Therefore, the mishna requires one to use something that has already been detached from the ground and reinserted. However, the previous mishna is referring to someone who placed his eiruv in a tree, where this concern is not relevant.

The Gemara relates that a certain army [pulmosa] once came to Neharde’a and took quarters in the study hall, so that there was not enough room for the students. Rav Naḥman said to the students: Go out and create seats by compressing reeds in the marshes, and tomorrow, on Shabbat, we will go and sit on them and study there.

Rami bar Ḥama raised an objection to Rav Naḥman, and some say that it was Rav Ukva bar Abba who raised the objection to Rav Naḥman, from the mishna that states that if the reed was detached and then stuck into the ground, yes; but if it was not detached and not stuck into the ground, no. This shows that it is not enough to compress the reeds, and they must actually be detached from the ground before they may be used on Shabbat.

Rav Naḥman said to him: There, in the mishna, we are dealing with hard reeds, which may not be bent and used on Shabbat, unlike soft reeds. He adds: And from where do you say that we distinguish between hard reeds and reeds that are not hard? As it was taught in a baraita: Reeds, boxthorn, and thistles are species of trees, and therefore they are not included in the prohibition of food crops in a vineyard, which applies only to herbs planted among vines. And it was taught in another baraita: Reeds, cassia, and bulrushes are species of herbs, and therefore they are included in the prohibition of food crops in a vineyard. These two baraitot contradict one another, as one states that reeds are trees, while the other says that they are considered herbs.

Rather, conclude from this that we must distinguish between them as follows: Here, in the first baraita, it is referring to hard reeds, which are like trees; whereas there, in the second baraita, it is referring to reeds that are not hard. The Gemara concludes: Indeed, conclude from this that our resolution of the contradiction is correct.

The Gemara raises a question with regard to the previously cited baraita: Is cassia a type of herb? Didn’t we learn in a mishna: One may not graft rue to white cassia, as this involves the grafting of herbs to a tree? This proves that white cassia is a tree. Rav Pappa said: There is no difficulty, as cassia is distinct and is considered a type of herb, and white cassia is distinct and is considered a type of tree.

MISHNA: If one put the eiruv in a cupboard and locked it, and the key was lost, so that he is now unable to open the cupboard and access the eiruv, it is nonetheless a valid eiruv. Rabbi Eliezer says: If he does not know that the key is in its place, it is not a valid eiruv.

GEMARA: The Gemara asks: And why should the eiruv be valid if the key was lost? He is in one place and his eiruv is in a different place, since he cannot access the eiruv.

It was Rav and Shmuel who both said: Here, we are dealing with a cupboard made of bricks, and the mishna is in accordance with the opinion of Rabbi Meir, who said: One may create a breach in a brick wall on Shabbat ab initio, and take produce from the other side. As we learned in a mishna: If a house filled with produce had been sealed and was then breached, one may take out produce from the place of the breach. Rabbi Meir disagrees and says: One may even create a breach in the wall of the house and take produce ab initio. Consequently, according to Rabbi Meir it is permissible to make a hole in the cupboard in order to remove the produce found inside.

The Gemara asks: Didn’t Rav Naḥman bar Adda say that Shmuel said that that very mishna cited as a proof is referring to a structure built from layers of bricks piled one atop the other without cement or mortar between them, in which case making a hole cannot be considered dismantling a bona fide structure? The Gemara answers: Here too, we are dealing with a cupboard made from layers of bricks.

The Gemara raises another difficulty: Didn’t Rabbi Zeira say: The Sages in the aforementioned mishna, who discussed the breaching of a wall, spoke only with regard to a Festival, but not with regard to Shabbat? Therefore, it cannot be derived from that mishna that it is permitted to breach the cupboard on Shabbat in order to access the food inside. The Gemara answers: Here too, the mishna is referring to a case where the person needed an eiruv for a Festival but not for Shabbat.

The Gemara asks: If it is so that the mishna is referring only to a Festival, there is a difficulty with that which was taught about it in the following Tosefta: Rabbi Eliezer says: If the key was lost in a city, his eiruv is a valid eiruv; and if it was lost in a field, his eiruv is not a valid eiruv, for within a city it is possible to carry the key by way of courtyards that have joined together in an eiruv or the like, but in a field it is impossible to carry it, as the field has the status of a karmelit. And if the mishna is referring to a Festival, what is the difference to me whether the key was lost in a city or a field? On a Festival there is no prohibition against carrying from a private to a public domain, and therefore if the key was lost even in a field, the eiruv should still be valid.