1) NOT "KEVA": SECHACH PLACED ON THE LEGS OF A BED
OPINIONS: In the Mishnah, the Tana Kama and Rebbi Yehudah disagree about a Sukah constructed by placing Sechach atop the legs of a bed. The Tana Kama says that such a Sukah is valid. Rebbi Yehudah says that it is not valid.
The Gemara gives two reasons for Rebbi Yehudah's opinion. According to one Amora, he invalidates the Sukah because it is not "Keva." Another Amora says that he invalidates the Sukah because it is supported by an object that can become Tamei (see following Insight).
What does the Gemara mean when it says that Rebbi Yehudah invalidates the Sukah because it is not "Keva"?
(a) RASHI explains that since the bed-poles support the Sukah, when one moves the bed the Sukah also moves, and a movable Sukah is not a "Diras Keva," a permanent dwelling place. Rebbi Yehudah invalidates this Sukah because he requires that a Sukah be a "Diras Keva" (7b).
However, the Mishnah later (22b, and cited on 7b) says that a Sukah may be built on top of a wagon or camel, which implies that a movable Sukah is valid. Rashi apparently maintains that Rebbi Yehudah disagrees with the Halachah expressed in that Mishnah, just as Raban Gamliel disagrees with it (TOSFOS DH she'Ein Lah). It is possible that Rebbi Yehudah agrees with the other ruling in the Mishnah there, that a Sukah built on a boat is valid, because in that case the Sukah is considered stationary and "Keva." A boat on water is never fully stationary, and thus any position of the boat is considered a stationary position (see Tosfos).
According to this explanation, the Halachah should not follow the view of Rebbi Yehudah in this case. A Sukah made by placing Sechach on the legs of a bed should be valid, because this is the Halachah with regard to the case of a Sukah atop a wagon.
The RAN gives a different answer to reconcile the ruling of the Mishnah later with Rebbi Yehudah's ruling. In the case of a Sukah on the legs of a bed, the floor of the Sukah is the ground beneath the bed; the Sechach is merely supported by the bed-poles. In that case, when the bed is moved, the Sechach is moved to cover an entirely different area of floor. In contrast, a Sukah built on a wagon has the floor of the wagon as its floor, and thus as the wagon moves the Sukah's floor moves with it and does not change. Therefore, even though the Halachah is that a Sukah on a wagon is valid, the Halachah can also follow the view of Rebbi Yehudah in the case of a Sukah on a bed (and the Sukah is invalid).
According to the Ran's explanation, when the Gemara concludes that the Sukah is valid when the Sechach is placed over the bed (and is not supported by the legs of the bed), it means that the Sechach is placed on the bed in such a way that the bed is the floor of the Sukah. When the bed moves, the floor of the Sukah also moves.
(b) TOSFOS and the RAMBAN quote the Yerushalmi and explain that "Keva" here means that this Sukah is not a residence in which one easily lives, because there are less than ten Tefachim from the top of the bed until the roof of the Sukah. Since it is not a residence that can be used in a normal way, it is not a valid Sukah.
(c) The RA'AVAD on the Rif explains that the Sukah is not on the bed itself, but rather the bed supports the Sukah on one side. When one moves the bed to sleep in it, the whole Sukah will tumble down. Therefore, it is like a Sukah which cannot endure a Ru'ach Metzuyah (a wind of ordinary strength; that is, normal usage will cause it to fall down). Such a Sukah is invalid (even according to those who permit a Sukah which is a "Diras Arai," on 22a).
2) NOT "MA'AMID": SECHACH PLACED ON THE LEGS OF A BED
QUESTIONS: In the Mishnah, the Tana Kama and Rebbi Yehudah disagree about a Sukah constructed by placing Sechach atop the legs of a bed. The Tana Kama says that such a Sukah is valid. Rebbi Yehudah says that it is not valid.
The Gemara gives two reasons for Rebbi Yehudah's opinion. According to one Amora, he invalidates the Sukah because it is not "Keva" (see previous Insight). Another Amora says that he invalidates the Sukah because it is supported by an object that can become Tamei.
RASHI explains that the object ("Ma'amid") which serves to support the Sechach is considered like the Sechach itself, and thus if it can become Tamei it is invalid, just like Sechach itself which can become Tamei. However, there are several sources that seem to contradict this law of Ma'amid:
(a) Rava (15b) discusses Sechach placed on metal rods atop a Sukah. He rules that when the Sechach is placed across the rods the Sukah is valid even though the Sechach is supported by the rods. Why is the Sukah valid? It should be invalid because the Sechach is supported by a Ma'amid which is Mekabel Tum'ah.
(b) The Mishnah (22b) says that a Sukah built atop a tree is valid. Why is it valid? The Sukah is supported by the tree, which is attached to the ground. Since any object attached to the ground is invalid for use as Sechach, a Ma'amid that is attached to the ground should invalidate the Sukah as well.
(c) Common practice is to allow the Sechach of a Sukah to be supported by a solid wall made of bricks or cement (manufactured from rock, sand, or clay). Those materials are not valid for use as Sechach (as the RITVA states on 4a, 11b, and at the end of 21b). Why, then, may such a wall be used as a Ma'amid?
(a) Apparently, Rava rules that Sechach may be supported by metal rods because he maintains that the reasoning for Rebbi Yehudah's ruling in the Mishnah here is that a Sukah built on top of the legs of a bed is not "Keva." Rava does not agree with the Amora who says that Rebbi Yehudah invalidates a Sukah built on the legs of a bed because the Ma'amid is Mekabel Tum'ah. Therefore, Rava permits Sechach to be supported on an object which is Mekabel Tum'ah. (KORBAN NESANEL)
(b) With regard to a Sukah built in a tree, the RA'AVAD explains that Sechach supported by a Ma'amid that is Mekabel Tum'ah is invalid only mid'Rabanan. The Rabanan enacted a Gezeirah to prevent people from thinking that just as an object which is Mekabel Tum'ah may be used as a Ma'amid, so, too, it may be used as the Sechach itself. Since it is an uncommon practice to build a Sukah in a tree, the Rabanan did not apply their Gezeirah in such a case.
The RAMBAN and RITVA answer that even if Sechach supported by a Ma'amid that is Mekabel Tum'ah is invalid mid'Oraisa, as Rashi says ("Ma'amid is considered like Sechach"), perhaps the Mishnah's case of a Sukah in a tree refers to Sechach that is supported by wooden boards, and those boards are supported by the tree. The tree itself does not directly support the Sechach; it merely supports the boards which in turn support the Sechach. Accordingly, the tree is "a Ma'amid of a Ma'amid" (Ritva; see following Insight), and therefore it is no different from every other Sukah which ultimately is supported by the ground (which may not be used for Sechach).
(c) The RAN suggests logical grounds for the common practice to use a solid wall (made of bricks or cement) to support the Sechach of a Sukah. First, it is highly uncommon that one uses earth or stone for the Sechach of a Sukah. Therefore the Ra'avad's reasoning (see (b) above) applies in this case as well.
Second, the Ran and Ritva explain that everyone knows that earth or stone cannot be used for Sechach, because such a roof is that of a permanent house and not that of a temporary Sukah. Since everyone knows that such material cannot be used for Sechach, there is no basis to prohibit it from being used as the Ma'amid for Sechach, because no one will confuse the Ma'amid with the Sechach. (This approach justifies the practice to support Sechach on a stone wall only according to the view of the Ra'avad, who says that the Isur of Ma'amid is mid'Rabanan. It does not justify the practice according to the view of Rashi, who maintains that the Isur of Ma'amid is mid'Oraisa.)
3) HALACHAH: "MA'AMID" AND "MA'AMID D'MA'AMID"
OPINIONS: In the Mishnah, Rebbi Yehudah says that a Sukah constructed by placing Sechach atop the legs of a bed is not valid. The Gemara gives two reasons for Rebbi Yehudah's opinion. According to one Amora, he invalidates the Sukah because it is not "Keva." Another Amora says that he invalidates the Sukah because it is supported by an object that can become Tamei. Since such an object may not be used as Sechach, it also may not be used to support the Sechach.
This issue is very relevant in practice. Is one permitted to use metal rods to support the Sechach of his Sukah? May one secure the Sechach by tying it with processed strings of cotton or linen? Similarly, may one use metal nails to hold down the boards which support the Sechach?
(a) In the Mishnah, the Rabanan argue with Rebbi Yehudah. The BA'AL HA'ME'OR rules that the Halachah follows the view of the Rabanan. He rules this way apparently because that opinion is the opinion of the majority, or, as the RA'AVAD explains the Ba'al ha'Me'or's intention, because the Mishnah later (22b) permits one to place Sechach on a portable object or on an object which may not be used as Sechach itself.
(b) Other Rishonim assert that since the Amora'im discuss the reason for Rebbi Yehudah's ruling, the Halachah follows his opinion. Accordingly, a Sukah built by placing Sechach on the legs of a bed is invalid. (According to the ROSH, the Rabanan and Rebbi Yehudah do not even argue; Rebbi Yehudah merely explains the opinion of the Rabanan.)
The Amora'im give two reasons for Rebbi Yehudah's opinion. The ROSH
says that the primary reason is because such a Sukah is not "Keva." He accepts the definition of "Keva" as explained by Tosfos and the Ramban in the name of the Yerushalmi (see Insights to 21:1:b
): Rebbi Yehudah disqualifies the Sukah because its Sechach is too low (it is less than ten Tefachim from the top of the bed) and thus it is not "Keva." This is how the SHULCHAN ARUCH
(OC 630:3) rules.
However, the RAMBAN, RITVA, and RAN rule stringently and maintain that the Halachah also follows the second reason -- that one may not support Sechach with an item that is Mekabel Tum'ah. The Shulchan Aruch (OC 629:7) indeed writes that it is questionable whether one may use a Ma'amid that is Mekabel Tum'ah. (Some, however, explain the words of the Shulchan Aruch differently. They explain that the Shulchan Aruch rules elsewhere (OC 628) that rods, which are Mekabel Tum'ah, may be used as a Ma'amid.)
HALACHAH: The SHA'AR HA'TZIYUN (OC 630:60) lists many Rishonim who place no limits on the type of Ma'amid that may be used to support the Sechach. Therefore, he concludes that although it is best to be stringent l'Chatchilah and use only a Ma'amid that is fit to serve as Sechach, b'Di'eved the Sukah is valid even with a Ma'amid that is Mekabel Tum'ah.
What is the Halachah with regard to a "Ma'amid d'Ma'amid" -- a Ma'amid of a Ma'amid? This refers to an object that supports the Ma'amid that in turn supports the Sechach. Is the Sukah valid when the object that supports the Ma'amid that supports the Sechach is itself not valid for Sechach?
The MAGEN AVRAHAM and the VILNA GA'ON (in his comments to the Shulchan Aruch OC 629:8) rule that a Ma'amid of a Ma'amid is permissible even though it can be Mekabel Tum'ah. The proof is that the Ramban, Ritva, and Ran -- who say that one should be stringent when it comes to a Ma'amid -- explain that if one supports the Sechach on wooden poles (a valid Ma'amid) that are supported by a bed, the Sukah is valid even though the bed is Mekabel Tum'ah and supports the Ma'amid (that is, the bed is a Ma'amid of a Ma'amid).
The CHAZON ISH (143:2), however, rules stringently, based on the Ramban. The Ramban permits the use of a Ma'amid of a Ma'amid that is Mekabel Tum'ah only because the Ma'amid (which is invalid as Sechach) is a horizontal surface that serves the same purpose as the ground ("Ma'aseh Karka b'Alma"). This reasoning applies, however, only when the invalid object serves as the floor of the Sukah. If the object stands upright and supports the Ma'amid of the Sechach, such as metal nails that hold down the beam that supports the Sechach, then that logic does not permit one to use a Ma'amid of a Ma'amid that is invalid for Sechach. (The RITVA presents the arguments of the Ramban slightly differently. According to the Ritva, the allowance to use a Ma'amid of a Ma'amid that is invalid for Sechach applies when the secondary Ma'amid is farther away from the Sechach than the primary Ma'amid, and not because it merely serves as the ground of the Sukah. Accordingly, the proof of the Chazon Ish may actually be the subject of a Machlokes Rishonim between the Ramban and Ritva.)
The Chazon Ish presents a second argument. He says that if the Ma'amid (even one which is valid for use as Sechach) of the Sechach rests on an object that is Mekabel Tum'ah, then that Ma'amid may no longer be used as Sechach. Consequently, the Sechach that rests on that Ma'amid is considered to rest on an object which cannot be used as Sechach (a domino effect), and thus the Sukah should be invalid.
However, it could be that this logic does not apply here to prohibit the use of a Ma'amid of a Ma'amid. These Rishonim (Ramban, Ritva, Ran) maintain that a Ma'amid that is Mekabel Tum'ah invalidates the Sukah only mid'Rabanan -- the Rabanan enacted a Gezeirah lest one err and think that he is permitted to use such material for the actual Sechach of the Sukah. Since the Pesul of a Ma'amid that is unfit for Sechach is only a Gezeirah d'Rabanan, the Rabanan limited their Gezeirah to an actual Ma'amid. They did not apply it to a secondary Ma'amid.
The Chazon Ish concludes that, in practice, one should be careful not to use even a Ma'amid of a Ma'amid that is Mekabel Tu'mah (except for the cases mentioned in the previous Insight, in which one is permitted to use material that is invalid for Sechach as a Ma'amid according to all opinions). As mentioned earlier, the Sha'ar ha'Tziyun writes that b'Di'eved the Sukah is valid.