Shade of a Sukka
The gemara (2a) provides two reasons why a sukka taller than twenty amot is invalid, pasul. Rabba says that if the sukka is that high, a person does not know that he is sitting inside a sukka. Rabbi Zeira notes that if the walls are that high, the sekhakh no longer provides shade; instead, the shade is provided by the towering walls. Citing a pasuk in Yeshayahu describing an apocalyptic sukka which will "provide shade," Rabbi Zeira claims that a sukka whose sekhakh does not provide shade - in this instance because the walls are too high - is pasul.
I would like to focus on Rabbi Zeira’s view. He seems to remind us of a basic and essential part of the mitzva of sukka. Although the architecture and material of a sukka may be appropriate, if a person does not sit under the SHADE of the sekhakh, he has not fulfilled the mitzva. This may appear to be the obvious explanation for Rabbi Zeira's opinion, but an ensuing question and retort may suggest a different view. Abaye questions Rabbi Zeira's position: After all, he claims, a person could theoretically sit in a sukka beneath a lofty mountain, despite the fact that the mountain provides shade and, effectively, he does not sit in the shade of the sekhakh. If a sukka beneath a mountain is valid, why shouldn't a sukka with walls higher than twenty amot be? Logically, a very simple distinction could be offered in response. A person must sit under man-made shelter or shade, regardless of what environmental or geological factors augment or diminish the "light source" being shaded. Just as clouds may dim the sunlight and reduce the "effect" of the shade, mountains may as well. The only diminishing factor that would invalidate the mitzva is a tree, since its primary purpose is precisely that of the sekhakh, rendering the latter redundant. Similar to a tree, a towering wall that eliminates sunlight effectively eliminates the sekhakh-reduced shade under which the mitzva must be fulfilled.
Although this seems to be the obvious solution, the gemara responds with what may be a different distinction. The gemara defends Rabbi Zeira's position by claiming that if the mountains were removed, the sekhakh would provide shade, whereas if the walls were removed, the sekhakh would fall and be unable to function as providing shade. As Rashi comments, since the sekhakh would fail in its function of shade provision in the absence of the walls, it loses its status as sekhakh.
The gemara may be suggesting a novel approach here. The mitzva of sukka does not have to be performed under SHADE; a person must merely sit under SEKHAKH. However, one of the conditions that define halakhic sekhakh is the ability to provide shade. Once sekhakh possess that potential, a person fulfills the mitzva solely by sitting under the sekhakh, even if, in theory, he does not sit within its shade. Sekhakh located under a mountain possesses the ABILITY to provide shade and is therefore deemed halakhic sekhakh, allowing for performance of the mitzva – even though the person does not sit in the actual shade of the sekhakh. In contrast, in a sukka taller than twenty amot, the sekhakh DEPENDS upon the walls architecturally; the sekhakh is incapable of providing shade alone. The sekhakh requires the walls, but those very same walls eliminate the sekhakh's shade providing potential. Effectively, this sekhakh no longer retains its status as sekhakh.
In essence, we have translated one question into another. The gemara disqualifies walls higher than twenty amot but validates sukkot near mountains. If we require the actual shade of the sekhakh, the difference between mountains and walls lies in the former being natural while the latter is artificial. If we do not require shade but just shade-potential, walls - integral elements of the sukka architecture - subvert that potential, while mountains do not.
One issue that may be affected by this chakira concerns a sukka whose walls are higher than twenty amot but whose sekhakh is attached to the walls at a point lower than twenty amot. The excess walls above twenty amot clearly "eclipse" the sekhakh, but the sekhakh is not dependent upon these walls. Must we disqualify the sukka since the eclipsing effect is produced by the walls and not by natural forces? Or can we dismiss this section of the wall as irrelevant, as we do to adjacent mountains, claiming that the integral sekhakh is valid independent of the upper portions of the walls?
Presumably, this question depends on the differing interpretations of the difference between mountains and towering walls. If the mountain can be dismissed because it provides natural shade, we would not be able to claim the same dismissal of walls towering above the sekhakh. The mitzva demands that shade be provided by the sekhakh, and that can not occur in this case. If, however, we dismiss mountains because the sekhakh is not reliant on them architecturally and can be viewed as an independent shade-producing element, we may make the same claim about the portion of the walls higher than the sekhakh. Since the sekhakh is not connected to these walls, it does not rely on them for support, and the sekhakh can therefore be viewed as a self-contained shade-producing element. If we only require that the sekhakh be CAPABLE of providing shade INDEPENDENTLY, regardless of whether or not one actually sits in its shade, this sukka would be valid.
This question regarding the nature of the relationship between sekhakh and shade and the reason that a sukka higher than twenty amot is disqualified may be discerned in an interesting difference between the Yerushalmi and Bavli. Each cites the halakha, but each provides a different source for the disqualification. The Bavli cites the aforementioned pasuk in Yeshayahu, which requires "tzel," shade. In contrast, the Yerushalmi mentions a pasuk in Emor that teaches that a person should sit "in a sukka," the literal translation of the word sukka referring to the actual sekhakh. According to the Bavli, Rabbi Zeira may require that a person sit under actual SHADE, whereas the Yerushalmi may only require him to sit under SHADE-CAPABLE SEKHAKH.
The question of the "role" of shade can be detected in a fascinating set of explanations provided by the Tosafot (2b), s.v. yesh ba. Although a sukka higher than twenty amot is pasul because the sekhakh does not provide shade, the gemara allows that a sukka more than 4x4 amot area may be as high as twenty amot since, inevitably, the sekhakh will provide shade. Tosafot question this claim since, at some point, excess height will once again prevent the sekhakh from producing any shade.
Tosafot answer this question in two manners. First, they claim that as the height increases, the ratio of height to surface area must be maintained proportionate to the twenty amot height to 4x4 amot area ratio. For example, if the surface area were to double to 8x8, the height could rise to 40 amot. This solution allows a proportion that will always enable the sekhakh to provide shade. Tosafot offer a second and more controversial approach as well. Although the height may rise, as long as the area is AT LEAST 4x4, the sekhakh will provide a modicum of shade, even though the primary shade is provided by the walls, and is therefore valid.
We may certainly question the physics of Tosafot, but that aside, logically why should a trace of shade provided by sekhakh be sufficient to validate the ENTIRE sukka?
Perhaps Tosafot's two replies debate our very issue - is the mitzva defined as sitting under shade or as sitting under shade-producing sekhakh? Tosafot's first answer views the mitzva as the former, and therefore requires that the twenty amot high/4x4 amot surface area ratio be maintained so that the ENTIRE shade will always be provided by the sekhakh. In their second reply, Tosafot view the mitzva as sitting under sekhakh, not under sekhakh's shade. Shade capability is necessary to qualify the sekhakh as halakhic potent; if the sekhakh is capable of providing even minor shade, it can be defined as sekhakh, and sitting under that sekhakh constitutes fulfillment of the mitzva. Tosafot's second answer is more willing to suffice even with minimal shade since the shade merely qualifies the sekhakh but is not ITSELF the object of the mitzva.
The validation of sekhakh with minimal shade production emerges from another interesting debate amongst the Rishonim. The Ritva questions the disqualification of a sukka higher than twenty amot, as even in this scenario the sekhakh provides shade at noontime, when the sun is directly overhead. Many Rishonim posed this question and offered a variety of creative solutions. The Ran, for example, claimed that although the sekhakh DOES shade the sukka at noon, because the sekhakh is so high, the shade only deters light but does not fully shelter from heat. Sekhakh must provide shelter from light as well as heat to be considered halakhic sekhakh.
Although many Rishonim wrestle with the concern of the Ritva, logically it does not seem to be so difficult. There may be ONE point of the day during which the sekhakh of a very tall sukka provides shade, but in a sukka higher than twenty amot, MOST shade-hours are provided by the walls and not the sekhakh. At most, it would seem, the sukka should be valid only during noontime, and perhaps not even then, since we may define the sukka status based on the shade production during most of the daytime hours. Why should shade production during a small fraction of daytime be sufficient to validate this sukka? Why do the Rishonim feel compelled to resolve this issue?
Perhaps their logic reiterates the logic suggested by Tosafot in their second reply. If the mitzva consists of sitting under sekhakh, and shade production is necessary merely to qualify the sekhakh as such, minimal and limited shade production suffices. Tosafot suggest a very extreme stance in this regard - even a towering sukka larger than 4x4 but not proportional is valid since there is a trace of shade provision by the sekhakh. Perhaps the Ritva and the other Rishonim reject Tosafot's extremism but embrace the logic; as long as the sekhakh provides primary shade – even during a limited time frame - we may deem the sekhakh as sekhakh and validate sitting under it, even when the sekhakh no longer provides ANY shade. The Ritva and others were forced to explain why this noontime provision of shade is not sufficient to validate the sekhakh because according to their logic, the sukka should be valid. If, however, we view the mitzva as sitting under the shade of sekhakh, the question appears less compelling.
Ultimately, the question of whether we are required to sit under actual shade or merely to sit under sekhakh capable of providing shade is an essential question that threads much of the discussion of the first two perakim of Sukka. Rabbi Zeira's contention that a twenty-amot-high sukka subverts the sekhakh and the gemara's ensuing debate underscores the centrality of this question.