The case of mortar that is liquid and can be poured proves that there are situations where items that themselves are unfit render other items fit, as, on the one hand, it combines with water to complete the requisite measure of forty se’a to render a ritual bath fit to purify. But, on the other hand, one who immerses in a bath filled only with mortar, the immersion does not fulfill his obligation.

MISHNA: One who establishes his sukka like a type of circular hut, with no roof whose walls slope down from the center or who rested the sukka against the wall, by taking long branches and placing one end on the ground and leaning the other end against the wall to establish a structure with no roof, Rabbi Eliezer deems it unfit because it does not have a roof, and the Rabbis deem it fit; as, in their opinion, the roof and the walls may be a single entity, indistinguishable from each other.

GEMARA: It was taught in a baraita: Rabbi Eliezer concedes that if one lifted one of these types of sukkot off the ground at least one handbreadth, thereby creating a vertical wall, or if one distanced the sukka resting against the wall one handbreadth from the wall, the sukka is fit. In these cases, the difference between the wall and the roof is conspicuous.

The Gemara asks: What is the rationale for the opinion of the Rabbis, who deem a sukka fit even where it is an inclined roof rather than a flat one? The Gemara answers: In their opinion, the legal status of the incline of a tent is like that of a tent. As long as it provides shelter, there is no need for a distinct, conspicuous roof for it to be a fit sukka.

It is related: Abaye found Rav Yosef, his teacher, who was sleeping inside a netted bridal canopy, whose netting inclines down, inside a sukka. Ostensibly, Rav Yosef did not fulfill his obligation, as he slept in the tent formed by the canopy and not directly in the sukka. Abaye said to him: In accordance with whose opinion do you hold, that you do not consider this netting a tent? Is it in accordance with the opinion of Rabbi Eliezer, who maintains that a structure without a distinct roof does not have the legal status of a tent, and therefore the netting does not constitute a barrier between the roofing of the sukka and the person sleeping below? Did you abandon the opinion of the Rabbis, who maintain that the netting constitutes a barrier because the legal status of a structure without a distinct roof is that of a tent, and act in accordance with the opinion of Rabbi Eliezer? In disputes between an individual Sage and multiple Sages, the halakha is in accordance with the multiple Sages, i.e., the Rabbis.

Rav Yosef said to him: In the baraita, the opposite is taught. Rabbi Eliezer deems it fit and the Rabbis deem it unfit. Abaye asked him: Did you abandon the mishna, whose formulation is authoritative, and act in accordance with a baraita, which may not be accurate?

Rav Yosef said to him: I have proof that the formulation of this particular baraita is precise, as the formulation of the mishna is an individual version of the dispute, and most of the Sages adopt the version of the baraita, as it is taught in another baraita: One who establishes his sukka like a type of circular hut or rests the sukka against the wall, Rabbi Natan says that Rabbi Eliezer deems the structure unfit because it does not have a roof, and the Rabbis deem it fit. Apparently, the mishna reflects only Rabbi Natan’s version of the argument. According to most of the Sages, the correct formulation of the dispute is that of the baraita: Rabbi Eliezer deems it fit and the Rabbis deem it unfit. The halakha is in accordance with the latter version of the dispute, and therefore it is permitted to sleep inside a bridal canopy in a sukka.

MISHNA: In the case of a large mat of reeds, if one initially produced it for the purpose of lying upon it, it is susceptible to ritual impurity like any other vessel, and therefore one may not roof a sukka with it. If one initially produced it for roofing, one may roof a sukka with it, and it is not susceptible to ritual impurity, as its legal status is not that of a vessel. Rabbi Eliezer says that the distinction between mats is based on use, not size. Therefore, with regard to both a small mat and a large mat, if one produced it for the purpose of lying upon it, it is susceptible to ritual impurity and one may not roof a sukka with it. If one produced it for roofing, one may roof a sukka with it, and it is not susceptible to ritual impurity.

GEMARA: The Gemara analyzes the formulation of the mishna and raises a difficulty. This mishna itself is difficult, as it contains an apparent contradiction. On the one hand, you said: If one produced it for the purpose of lying upon it, it is susceptible to ritual impurity and one may not roof a sukka with it. The reason it is unfit for roofing is due to the fact that one produced it specifically for the purpose of lying upon it. Presumably, a mat produced without designation is for roofing, and therefore one may roof a sukka with it.

And then it is taught in the mishna: If one produced it for roofing, one may roof a sukka with it, and it is not susceptible to ritual impurity. The reason it is fit roofing is due to the fact that one produced it specifically for roofing. This implies that a mat that one produced without designation is presumably for the purpose of lying upon it, and therefore one may not roof a sukka with it. The inferences drawn from these two clauses in the mishna about a mat produced without designation contradict each other.

The Gemara answers: This is not difficult. Here, in the first clause of the mishna, it is referring to a large mat, which is typically not produced for the purpose of lying upon it. Therefore, it is unfit for roofing only if it is produced specifically for the purpose of lying upon it. If it is produced without designation, it is presumably for roofing, and one may roof a sukka with it. There, in the second clause of the mishna, it is referring to a small mat, which is typically not produced for roofing. Therefore, one may roof a sukka with it only if it is produced specifically for roofing. If it is produced without designation, it is presumably for the purpose of lying upon it, and one may not roof a sukka with it.

The Gemara notes: Granted, according to the Rabbis this is not difficult; as the above distinction resolves the apparent contradiction in the mishna. However, according to Rabbi Eliezer, the contradiction remains difficult, as we learned in a mishna that Rabbi Eliezer says: With regard to both a small mat and a large mat, if one produced it for the purpose of lying upon it, it is susceptible to ritual impurity and one may not roof a sukka with it. The reason it is unfit for roofing is due to the fact that one produced it specifically for the purpose of lying upon it. This implies that a mat that one produced without designation is presumably for roofing, and therefore one may roof a sukka with it.

And say that in the latter clause of the mishna, where Rabbi Eliezer continues: If one produced it for roofing, one may roof a sukka with it and it is not susceptible to ritual impurity, the reason it is fit roofing is due to the fact that one produced it specifically for roofing. However, by inference, a mat that one produced without designation is presumably for the purpose of lying upon it, and therefore one may not roof a sukka with it. The inferences drawn from these two clauses in the mishna contradict each other. The resolution cited above cannot resolve the contradiction according to Rabbi Eliezer, as he does not distinguish between a large mat and a small mat.

Rather, Rava said: The above resolution is rejected. With regard to a large mat, everyone agrees that if it was produced without designation, presumably it is for roofing. Where they disagree, is with regard to a small mat: The first tanna holds that a small mat produced without designation is presumably for the purpose of lying upon it, and Rabbi Eliezer holds that a small mat produced without designation is also presumably for roofing.