MISHNA: With regard to one who establishes his sukka beneath a tree, it is as though he established it inside the house and it is unfit. If one established a sukka atop another sukka, the upper sukka is fit and the lower sukka is unfit. Rabbi Yehuda says: If there are no residents in the upper sukka, the lower sukka is fit.

GEMARA: Rava said: They taught this halakha that a sukka beneath a tree is unfit only with regard to a tree whose shade is greater than its sunlight, as the source of the shade in the sukka is the tree and not the roofing. However, if its sunlight is greater than its shade, the sukka is fit, as in that case the roofing provides the shade.

The Gemara asks: From where does Rava reach this conclusion? The Gemara answers: He learns this from the fact that the mishna teaches: It is as though he established it inside the house. Why do I need the mishna to teach: It is as though he established it inside the house? Let the mishna teach simply: It is unfit. Rather, this is teaching us that in the context of this halakha, a tree is similar to a house; just as with regard to a house, its shade is greater than its sunlight, so too, with regard to a tree, it invalidates the sukka only if its shade is greater than its sunlight.

The Gemara asks: And even if the sunlight is greater than the shade of the tree, what of it? Why does Rava deem the sukka beneath the tree fit in that case? Isn’t there unfit roofing, the uncut branches of the tree, joining together with the fit roofing on the sukka, rendering even the fit roofing on the sukka unfit? Rav Pappa said: This is referring to a case where one lowered the uncut branches and combined them with the fit roofing so that the branches still attached to the tree are inconspicuous. Given that the majority of the roofing is fit, the roofing in its entirety is fit.

The Gemara asks: If it is a case where he lowered them, what is the purpose of stating this halakha? Isn’t it self-evident? The Gemara answers that it is necessary lest you say: Let us issue a decree and deem the roofing unfit in a case where one lowered them due to a case where one did not lower them. Therefore, it teaches us that we do not issue such a decree.

The Gemara asks: That halakha, too, we already learned in a mishna: If one trellised the grapevine, the gourd, or the ivy, climbing plants, over a sukka while they are still attached to the ground, and he then added roofing atop them, the sukka is unfit, as roofing attached to the ground is unfit. If the amount of fit roofing was greater than the plants attached to the ground, or if he cut the climbing plants so that they were no longer attached to the ground, it is fit.

The Gemara clarifies the details of the mishna: What are the circumstances? If we say that it is referring to a case where he did not lower the climbing plants and combine them with the fit roofing, doesn’t the unfit roofing join together with the fit roofing on the sukka, rendering even the fit roofing on the sukka unfit? Rather, isn’t the mishna referring to a case where he lowered them, and conclude from this mishna that we do not issue a decree in a case where he lowered the branches due to a case where he did not lower the branches. Rava’s statement is therefore unnecessary. The Gemara answers: Lest you say that this applies only after the fact, i.e., that if one already lowered the uncut branches or plants it is not unfit, but one may not do so ab initio; therefore, Rava teaches us that one may place roofing in this manner even ab initio.

§ The mishna continues: If one established a sukka atop another sukka, the upper sukka is fit and the lower sukka is unfit. The Sages taught in a baraita that the verse states: “In sukkot shall you reside” (Leviticus 23:42), and not in a sukka that is beneath another sukka, and not in sukka that is beneath a tree, and not in a sukka that is inside a house.

The Gemara questions that derivation. On the contrary, the term “in sukkot,” which is written in the plural, indicates two. The conclusion should be that one sitting inside a sukka beneath a sukka fulfills the mitzva. Rav Naḥman bar Yitzḥak said: Although the term is vocalized in the plural, basukkot is written without the vav, indicating a single sukka.

Rabbi Yirmeya said: There are times when both of the sukkot one atop the other are fit; there are times when both of the sukkot are unfit; there are times when the lower sukka is fit and the upper sukka is unfit; and there are times when the lower sukka is unfit and the upper sukka is fit.

The Gemara elaborates: There are times when both of the sukkot one atop the other are fit. What are the circumstances? It is in a case where in the lower sukka its sunlight is greater than its shade, rendering the sukka unfit, and in the upper sukka its shade is greater than its sunlight, rendering the sukka fit. And the roofing of the upper sukka is within twenty cubits of the ground. In that case, the roofing of the upper sukka is effective for both the upper sukka and the lower one.

There are times when both of the sukkot are unfit. What are the circumstances? It is in a case where in both sukkot, their shade is greater than their sunlight, but the upper one is more than twenty cubits above the roofing of the lower sukka, rendering it unfit. Since the roofing of the upper sukka is unfit, and it casts shade over the lower sukka, the lower sukka is also unfit.

There are times when the lower sukka is fit and the upper sukka is unfit.