QUESTION: The Gemara discusses the laws of the various cases of one Sukah under another Sukah. The Gemara says that when the lower Sukah has more shade than sunlight and the upper Sukah has more sunlight than shade, and both are within 20 Amos of the ground, the upper Sukah is invalid (one may not eat in the upper Sukah) because there is more sunlight than shade in that Sukah. The lower Sukah is valid because there is nothing above it to invalidate it. (Rashi explains that the Sechach of the upper Sukah is not considered Sechach at all, since it lets in more sunlight than shade.)

The Gemara points out that it is not obvious that the lower Sukah is valid. One might have thought that the Rabanan invalidated the lower Sukah in order to prevent someone from assuming that he may use invalid Sechach together with valid Sechach for his Sukah. The Gemara teaches that there is no such Gezeirah, and there is no concern that someone will make that mistake.

Rashi explains that the Gemara's initial assumption is that there is a concern that one might sit in the lower Sukah even when the upper Sukah is taller than 20 Amos (in which case the Sechach of the upper Sukah is invalid and joins with the Sechach of the lower Sukah to invalidate the lower Sukah).

Why is there a concern that a person may sit in the lower Sukah even when the Sechach of the upper Sukah is higher than 20 Amos? If such a concern exists, then every Sukah should be invalid out of concern that one will sit in it even when its roof is higher than 20 Amos.

(a) RASHI (DH Tachtonah Kesherah) explains that the Gezeirah would apply only in this case, because the lower Sukah has all that it needs to make it valid (as it has more shade than sunlight). Only in this case are there grounds for concern that that one might forget that the upper Sukah potentially can invalidate the lower Sukah. (That is, one might ignore the upper Sukah, since it is not a full, valid Sukah.)

(b) RABEINU TAM, cited by Tosfos (9b, DH Ha), says that Rashi's explanation is forced. Rabeinu Tam explains the Gemara based on a different Girsa. According to his Girsa, the Gemara does not say that both the lower and upper Sukos are within 20 Amos, but that the lower Sukah is within 20 Amos (which implies that the upper Sukah is taller than 20 Amos). (The RITVA here and the BA'AL HA'ME'OR (2a) cite a similar Girsa in which the Gemara states explicitly that the upper Sukah is taller than 20 Amos, which is the same as saying that the lower Sukah is below 20 Amos.)

According to Rabeinu Tam, the Sechach of the upper Sukah -- which has more sunlight than shade -- is above 20 Amos, and nevertheless the lower Sukah is valid because the Sechach of the upper Sukah does not invalidate it. He explains that Sechach which is above 20 Amos is not considered invalid Sechach; it is the Sukah which is invalid, because it is a "Diras Keva." The Sechach itself is not Pasul. Therefore, the Sechach above does not invalidate the Sechach of the lower Sukah.

Rabeinu Tam's explanation is novel in that there is no Gezeirah that invalidates the lower Sukah in such a case. Even though someone might confuse this case (of a Sukah underneath another Sukah which is taller than 20 Amos) with a case of a Sukah underneath a tree and think that such a Sukah is valid, the Rabanan were not concerned for such an error and made no Gezeirah to invalidate the lower Sukah.

(c) The RA'AVAD (in his comments on the Ba'al ha'Me'or, 2a) has the same text of the Gemara as the Ritva (see (b) above), that the Sechach of the upper Sukah is higher than 20 Amos. The Ra'avad argues with Rabeinu Tam and says that Sechach higher than 20 Amos is invalid. He explains, however, that the reason the lower Sukah is valid in this case is because the pieces of invalid Sechach that are above 20 Amos are positioned between the pieces of the valid Sechach below, and therefore the lower Sukah still has a majority of shade even after the shade created by the upper (and invalid) Sechach is removed.

According to the Ra'avad, the Gemara's answer of "b'she'Chavtan" means that one makes each piece of Sechach the only layer. This is also the Rambam's understanding (Hilchos Sukah 5:13, according to the Magid Mishneh). We might have thought that the Rabanan invalidated the lower Sukah lest one think that it is valid even when the Sechach of the upper Sukah is directly above the Sechach of the lower Sukah. The Gemara teaches that the Rabanan were not concerned for such an error.

QUESTION: Rav Huna says that in order for the lower Sukah to be invalid because it is a Sukah underneath a Sukah, the distance between the Sechach of the upper Sukah and the Sechach of the lower Sukah must be at least one Tefach. He derives this figure from the laws of Tum'as Ohel, in which a covering is considered an Ohel only when the space below it is at least one cubic Tefach.

RASHI (DH Tefach Al Tefach) explains that there are two practical ramifications for the law that a covering is considered an Ohel only when there is a cubic Tefach of open space below it. First, since the covering is not an Ohel when the space is less than one cubic Tefach, it does not spread the Tum'ah from one point to another under the covering. Second, if there is an object on top of the covering, the Tum'ah will penetrate through the covering, since there is no Ohel to block the Tum'ah. Rashi adds that when there is less than a Tefach between the object of Tum'ah and the covering above it, it is called "Tum'ah Retzutzah" and it penetrates through the covering and rises.

Why does Rashi mention the principle of "Tum'ah Retzutzah"? Even without that principle, there is nothing to stop the Tum'ah from rising upwards beyond the covering, because the covering does not have the status of an Ohel (since there is not a Tefach of space beneath it). Why does Rashi mention that the Tum'ah penetrates the covering because of the principle of "Tum'ah Retzutzah," which teaches that Tum'ah actively penetrates the covering above it? No active force to push the Tum'ah through the covering is needed here, because the Tum'ah continues by itself through the covering since it is not considered an Ohel or an intervening partition.

ANSWER: The question assumes that the only thing that can stop Tum'ah from spreading upwards is an Ohel. Without an Ohel, the Tum'ah spreads upwards by itself. Ha'Ga'on Rav Moshe Shapiro shlit'a pointed out that the Gemara in Chulin (125b) teaches that a covering which is not an Ohel can also stop Tum'ah from spreading upwards under certain circumstances. The Gemara there says that Rebbi Yosi maintains that when one places a rope within one Tefach above a corpse, an object that passes above the rope and serves as an Ohel (Ma'ahil) over the corpse does not become Tamei. Rebbi Yosi maintains that Tum'ah cannot break through any intervening substance and rise ("Boka'as v'Olah"). In such a case, there is no Ohel that stops the Tum'ah from spreading, and yet the Tum'ah does not reach above the covering. The logic behind this is that the object that is above the covering does not serve as an Ohel (Ma'ahil) over the corpse, but rather it serves as an Ohel over the covering which is over the corpse (and whatever is beneath the covering is inconsequential). This is why Rashi must mention the additional principle of "Tum'ah Retzutzah"; even though there is no Ohel here, the Tum'ah still would not spread above the covering unless there is another force that pushes it through -- and that is the force of "Tum'ah Retzutzah."

(One might ask that the Mishnah in Ohalos (6:1) says that if a utensil that can be Mekabel Tum'ah is even a few Tefachim above a corpse, it does not stop the Tum'ah from spreading upwards. The utensil itself cannot stop the Tum'ah from spreading, because an object which can become Tamei itself cannot block Tum'ah from spreading. However, it should be able to block the Tum'ah from rising. If a covering stops Tum'ah from rising even when it is not an Ohel, then a utensil should also stop Tum'ah from rising (even though it can be Mekabel Tum'ah itself). It must be that the type of covering that can stop Tum'ah from spreading is only a type that cannot become Tamei. If the covering itself can become Tamei (like a utensil), then whatever is Ma'ahil over that covering is considered as though it is Ma'ahil over the corpse itself.)

The Acharonim point out that there are additional consequences of the rule of "Tum'ah Retzutzah," the positive force that pushes Tum'ah upwards (and downwards) when it is "squeezed" into less than a Tefach. First, the Torah teaches that a tightly sealed, earthenware vessel ("Tzamid Pasil") blocks Tum'as Mes in an Ohel from being Metamei an object inside of the vessel. However, a "Tzamid Pasil" which is above a "Tum'ah Retzutzah" does become Tamei (RASH, end of Ohalos 9, based on the Tosefta); the force of the "Tum'ah Retzutzah" pushes the Tum'ah through the sealed vessel. Second, a person who stands above a "Tum'ah Retzutzah" is considered as though he touches the Tum'ah and not merely as though he serves as an Ohel over it, since the presence of the Tum'ah is considered to fill the entire space above the intervening object (as the Gemara says in Chulin 125b). The VILNA GA'ON (Parshas Chukas) says that even though non-Jews transfer Tum'ah only through Maga and not through Ohel, they can still transfer Tum'ah with "Tum'ah Retzutzah" (that is, if a Jew touches a stone or object that is less than a Tefach above the non-Jew), because "Tum'ah Retzutzah" is like Maga.

QUESTION: The Gemara relates that Rav Ashi told his servant Minyamin to take down a wet cloak that Minyamin had spread on top of the Sechach to dry. Rav Ashi told him to take it down after it became dry so that people would not think that the Sechach is valid while the cloak is on top of it. He did not insist that it be removed while still wet, because while it is still wet everyone realizes that it was put there to dry and not to serve as Sechach.

It is not clear why Rav Ashi permitted the cloak to remain on the Sechach while it was wet. Even though onlookers realize that it was placed there to dry and not to serve as Sechach, the cloak on top of the Sechach should be no different from a tree above a Sukah. Just as the tree's branches (which are invalid Sechach) annul (Mevatel) the valid Sechach beneath them, the cloak should also annul the valid Sechach beneath it. The Mishnah itself (10a) says that when one places a sheet on top of the Sukah to protect it from the sun, the Sukah becomes invalid for this reason. What is the difference between a sheet placed on the Sechach to protect the Sukah from the sun and a cloak spread out on the Sechach to dry?

(a) RASHI (DH Lo Shena) seems to address this question. Rashi writes that when one spreads a sheet on top of the Sechach in order to protect it from the sun, he intends to use the sheet to shield what is beneath it. Since the sheet's purpose is to shield or protect, it serves the same purpose as the Sechach. Accordingly, it can annul the valid Sechach. (It does not become secondary and annulled to the Sechach, but rather it annuls the Sechach.) In contrast, when an object is placed on the Sechach to dry, it does not disqualify the Sechach because its purpose is not the same as the purpose of Sechach; it does not serve to protect anything beneath it. Therefore, it becomes annulled to the Sechach, just as a sheet that serves as a decoration for the Sukah becomes annulled to the Sukah.

The RITVA similarly says that a cloak placed on the Sechach to dry is not comparable to a sheet placed on the Sechach to shield the Sukah from the sun or to a sheet placed beneath the Sechach to catch falling pieces of Sechach. A sheet that shields the Sukah from the sun or that catches the falling objects is something that is needed for the Sukah, and therefore it is not considered a temporary addition. A cloak that is spread out to dry does not serve the Sukah, and thus is considered a temporary addition that does not invalidate the Sechach. It becomes annulled to the Sechach even if it serves no decorative purpose.

(b) Other Rishonim do not differentiate between a protective covering and a cloak or sheet spread out to dry. The only thing that is annulled to the Sechach is a decorative object, in which case it serves the Sechach by beautifying it and thus it is annulled to the Sechach. Anything that does not serve the Sechach is not annulled to the Sechach (see Hagahos Ashiri). Why, then, does a wet cloak not invalidate the Sechach?

TOSFOS (10a, DH Pires) explains that when the Sukah has more shade than sunlight, nothing spread on top of it will invalidate it, even if the object spread on the Sechach makes more shade. In the Mishnah, the reason why the Sukah is invalid when a sheet is placed on top of it is because the Sechach of the Sukah let in more sunlight than shade before the sheet was placed there (TESHUVAS HA'GE'ONIM), or because the sheet itself causes the Sechach to make more shade than sunlight (either by holding up the leaves or branches that became bent, or by protecting the Sechach from the sun so that it does not dry out) (RABEINU TAM). The Sechach of Rav Ashi's Sukah made more shade than sunlight, and thus it was not affected by a wet cloak on top of it. (See Insights to Sukah 9:2:b.)

(c) The BA'AL HA'ME'OR explains that when a Sukah had more shade before a foreign object (invalid Sechach which lets in more sunlight than shade) was placed on top of it, then it remains valid even if one adds invalid Sechach afterwards. In the case of Rav Ashi, Minyamin put the cloak up after the valid Sechach was placed on the Sukah, and thus the cloak did not invalidate the Sechach, since it covered only a small part of the Sukah. In the Mishnah, the sheet that was placed atop the Sechach made more shade than sunlight, and invalid Sechach that makes more shade always invalidates what is below it. (See Insights to Sukah 9:2:c.)

(d) The RITVA and RAN explain that Rav Ashi was not in his Sukah at the time, and therefore he was not concerned that something was on top of the Sukah. The cloak certainly invalidated the Sukah, but since Rav Ashi was not eating there he did not need the Sukah to be valid.

According to the Ritva and Ran, if Rav Ashi did not need a valid Sukah, then what difference does it make if the cloak is wet or dry? The answer is that if the cloak is wet, no one will eat in that Sukah, as the water from the cloak will drip on anyone below. Consequently, anyone who sees the Sukah empty of occupants will not mistakenly think that the Sukah is valid. If, however, the cloak is dry, then one might think that Rav Ashi intended to eat in the Sukah, and he will assume that a cloak is a valid form of Sechach. Therefore, Rav Ashi required the cloak to be removed once it dried.