QUESTION: The Gemara quotes the Mishnah in Kelim (18:9) in which the Chachamim teach that a slat and two legs of a bed are Mekabel Tum'ah, according to the interpretation of Rebbi Chanan in the name of Rebbi. In the Mishnah there, Rebbi Eliezer states that a bed becomes Tamei only when it is a "Chavilah," completely assembled into one unit. Similarly, Rebbi Eliezer maintains that in order to be Metaher the bed from its Tum'ah, the entire bed must be immersed in a Mikvah as one unit.
RASHI explains that the bed can become Tamei only when it is whole. If the bed is dismantled into parts, those parts cannot become Tamei. Even if a slat remains with two legs attached to it, which is a significant part of the bed and can be used on its own by leaning it against a wall, nevertheless it is not considered a complete Kli with a normal use and it cannot be Mekabel Tum'ah. When Rebbi Eliezer says that a bed can become Tahor only as a "Chavilah," he means that if a bed that became Tamei is dismantled and then immersed, it does not become Tahor.
Rashi's words are unclear. If, according to Rebbi Eliezer, a bed that is dismantled into separate parts is no longer considered a Kli, it should lose its Tum'ah just as any Kli loses its Tum'ah when it is broken (because it is no longer a Kli). Why does Rebbi Eliezer say that the separate pieces of a dismantled bed must be reassembled and then immersed in order to become Tahor?
(a) TOSFOS, the ROSH, and the RASH (in Kelim) explain that, indeed, Rebbi Eliezer maintains that a bed that is Tamei becomes Tahor when it is dismantled. Nevertheless, when the bed is reassembled, it returns to its state of Tum'ah and needs Tevilah. Tevilah is not effective while the bed is dismantled, because the Tum'ah does not return until it is reassembled.
This answer is problematic for two reasons. First, as the RASH himself asks, the beginning of the Mishnah in Kelim explicitly says that if half of a bed was stolen, when one recovers the stolen part and reassembles the bed, it does not return to its previous state of Tum'ah.
Second, the Mishnah earlier in Kelim (11:1) says that the only type of Kli which returns to its old Tum'ah when it is repaired is a metal Kli. All other types of Kelim become Tahor when they are taken apart and remain Tahor when reassembled. A wooden bed, therefore, should also remain Tahor when reassembled. (VILNA GA'ON to Kelim 18:7)
To answer the first question, the RASH says that when half a bed is stolen, the owner despairs of ever recovering that half and reassembling his bed. Therefore, the bed is considered as though it is irrevocably destroyed. Consequently, even if one eventually does put it back together, it does not return to its old Tum'ah. In contrast, when the owner of the bed disassembles the bed himself, all of the pieces are available, and the owner does not despair of reassembling it. Accordingly, it returns to its old Tum'ah when reassembled.
The Rash's explanation may also answer the second question. Although broken Kelim (that are not made of metal) normally do not become Tamei when they are reassembled, a wooden bed is different. Since it is common to dismantle and reassemble a bed, it is not considered a broken Kli when it is dismantled, and thus it returns to its Tum'ah when it is reassembled. Why, though, does the bed not become Tamei when it is dismantled, if it is not considered broken? Rebbi Eliezer teaches that in order for a Kli to become Tamei, not only must it not be broken, but it must also be usable. Even though a dismantled bed is not considered broken, it does not become Tamei because it is not usable in its present state.
(b) The VILNA GA'ON (Kelim 18:7 and 9) explains that when Rebbi Eliezer says that the bed becomes Tamei only when it is complete, he does not mean that when it is dismantled it becomes Tahor. Rather, if it was already Tamei before it was dismantled, its parts remain Tamei when dismantled, because it is not considered to be a broken Kli. However, if the bed was Tahor when it was dismantled, and now a part of the bed touches something that is Tamei, it cannot become Tamei. The parts of a dismantled bed cannot acquire new Tum'ah.
Rebbi Eliezer's statement that the bed becomes Tahor only when it is whole means that it becomes Tahor only when it is reassembled, but until then it remains Tamei. (The bed cannot be immersed in its disassembled state, because it is Tamei only due to what it used to be (a usable bed); it can become Tahor only when it is in the same state that it was in when it became Tamei.)
(c) TOSFOS and the RASH cite sources from the Tosefta for an entirely different way to understand Rebbi Eliezer's statement. Rebbi Eliezer does not mean that a bed becomes Tamei only when it is assembled. Rather, he means that it becomes Tamei even when it is assembled. "Chavilah" does not mean that the bed is completely assembled; rather, it means that as little as one slat and two legs ("Aruchah u'Shnei Kera'ayim") are assembled. Rebbi Eliezer maintains that any part of a bed that is dismantled not only remains Tamei, but even can become Tamei. When the parts of the bed are attached to each other and a Tamei person touches one part of the bed, that part becomes Tamei and spreads Tum'ah to the entire bundle of pieces.
The Chachamim argue and say that only the parts that were touched become Tamei. Those parts do not transfer the Tum'ah to other pieces attached to them. Since the bed is not whole, it is not considered a single, cohesive unit that can spread Tum'ah to all of its parts. Only when the bed is completely assembled can the entire bed become Tamei when any part of it is touched by a person who is Tamei.
When Rebbi Eliezer says that a bed becomes Tahor only when it is a "Chavilah," he means that since an "Aruchah u'Shnei Kera'ayim" are considered a cohesive unit, one may immerse the bundle together, and the point at which they are connected is not considered a Chatzitzah, an intervention that invalidates the Tevilah. The Chachamim argue and say that each part of the Tamei bed must be immersed separately, because the points at which they are connected are considered Chatzitzos. Only when all the parts are assembled into a complete bed is the entire bed viewed as a single unit and may be immersed as one. When the parts are not completely assembled into one complete bed, each piece is viewed as a separate part and must be immersed by itself.