Ohalos, Chapter 11, Mishnah 3. This Mishnah picks up exactly where the previous one left off, so we need the scene in front of us. The subject is an exedra, and the easiest way to imagine it is a roofed shelter of the sort one waits under for a bus: walls on three of its sides, each descending until it meets the ground, while the fourth side is left entirely open. The difficulty lies in the covering overhead, which is split by a crack running through its middle. Halachically, then, we have two roofs and not one, and the practical result is that tumah found beneath one of them will not be metameh whatever lies beneath the other.
What the earlier Mishnah discussed was a reed laid on the floor of the exedra, positioned right below that crack. So long as the reed simply lies flat on the floor, the situation is unchanged: two roofs, and tumah remains on the side where it is. Should the reed be suspended so that a tefach of space opens up beneath it, however, we apply gud asik or gud achis: either the reed is viewed as rising until it meets the covering, or the covering as descending until it meets the reed. Either way the crack is considered closed, the two roofs merge into one ohel, and tumah beneath either half now reaches the other half.
Case One: One Thick Object Resting on the Floor
Our Mishnah pushes the shaileh further. Its opening words are "sagos aveh vekoras aveh," a heavy woolen cloak or a thick wooden beam. One of these has been set down on the exedra's floor, lying directly beneath the s'chach along the line of the crack above. Unlike a reed, such an item has real bulk to it. Run a measurement from where it meets the floor up to its uppermost surface and you will find a full tefach. Its top, in other words, genuinely stands a tefach high, while its underside is pressed flat against the ground.
The Mishnah's chiddush now follows. Although the upper surface of this object does stand a tefach high, the fact that it is planted on the floor with no space at all below it means that it fails to unite the two roofs. In the Mishnah's words, "einan mevi'os es hatumah": such items do not carry tumah across to the far half of the exedra. What the halachah demands is genuine open space underneath, "ad sheyehu gevohim min ha'aretz posei'ach tefach," that the object be lifted until a hollow tefach opens beneath it. Bulk by itself achieves nothing. Only an item actually held a tefach clear of the floor allows us to say gud achis or gud asik, treat the split as closed, and regard the covering as a single roof.
Case Two: Garments Folded One Upon Another
A second case follows: "kefulim zu al gabei zu." Someone takes a number of garments and stacks them in folded layers, one over the next, and sets the whole pile on the floor beneath the opening in the covering. Here too the Mishnah rules "einam mevi'im es hatumah": the stack does not transmit tumah across the exedra. It does so only, in the Mishnah's language, "ad sheyehei elyonah gevohah min ha'aretz posei'ach tefach," when the lowest edge of the garment on top is a tefach above the floor.
The chiddush here is striking. Lema'aseh there is not a drop of air below that topmost beged: the garments beneath it occupy every bit of the space. Even so, because we have before us a number of separate items rather than a single solid mass, the halachah lets us take our measurement from the underside of the uppermost garment straight down to the floor. Should that come to a tefach, the top garment is considered elevated by a tefach, and the layers filling the space do not spoil it. That is sufficient for gud achis or gud asik, and the tear in the ceiling is sealed halachically.
Picture someone approaching with a practical question: there are things lying on the floor of the exedra, a tefach tall, exactly under the break in the ceiling. Have they closed it, so that both halves form one ohel? Our Mishnah answers that it depends on what is lying there. A lone object, a single beam or one heavy garment, accomplishes nothing unless it has been physically lifted a tefach clear of the floor; its own tefach of thickness is worthless while it rests on the ground. Where several garments are stacked in layers, however, the measurement is taken from the base of the highest one down to the floor. Reaching a tefach in that fashion is enough, even though garments and not air occupy the intervening space, and the break above is closed, whether one prefers to describe the pile as rising or the roof as coming down.
Case Three: A Person Lying Under the Gap
The Mishnah's third case is a person: "hayah adam nasun sham," a man is lying on the floor of the exedra, stretched out directly opposite the gap in the roof. Beis Shammai and Beis Hillel disagree.
Beis Shammai rule "eino meivi es hatumah": the man does not transmit tumah to the other side. In their view a human body constitutes one indivisible unit, precisely like the object of the Mishnah's opening case. His body may well be thicker than a tefach, but that puts him in no better position than a beam of a tefach's thickness resting on the floor. Since he himself lies on the ground and is not held a tefach above it, he does not close the covering.
Beis Hillel argue otherwise: "adam chalul hu," a human being is treated as hollow, not as one solid gush. A man stretched out there is thus domeh to a stack of folded garments, and the ruling is "vetzad ha'elyon meivi es hatumah," the upper side of him conveys the tumah across. Exactly as the garment on top of a pile conveys tumah because a tefach separates its underside from the floor, so here: from below the upper portion of his body down to the ground there is a tefach or more, and his body is not judged as a single mass. That internal tefach serves as the tefach of space beneath, and it suffices to seal the crack above.
A Refinement of the Tosfos Yom Tov
The Tosfos Yom Tov supplies an important limitation. Beis Shammai's ruling that the man does not convey the tumah applies specifically to a person lying there with nothing over him. Were a beged spread over him, Beis Shammai too would be modeh that tumah passes across, since a tefach separates the underside of that covering garment from the floor. The rule throughout is that once we have two distinct entities rather than one, the measurement may begin at the base of the upper one.
The Source for Beis Hillel
What leads Beis Hillel to say that a human being is not one solid gush? The Mishnah Acharonah, along with other mefarshim, cites a posuk in Iyov. Iyov declares, "Or uvasar talbisheini," You dressed me in skin and flesh, "uva'atzamos vegiddim tesochecheini," and with bone and sinew You roofed me over. The verb Iyov chose, "tesochecheini," shares its root with s'chach, which teaches that the body possesses a s'chach, a roof spread over whatever is inside it. A human being is accordingly not one uniform block but contents housed beneath a covering. And since he consists of distinguishable parts, the tefach is measured from the part that lies on top.
Summary
We are inside an exedra: three of its sides walled down to the ground, the fourth wide open, and a split running through its roof. Our interest is in keeping that split halachically open, so that tumah on one side will not travel to its neighbor. The preceding Mishnah established that a reed set down on the floor below the split closes nothing, so long as it has not been lifted so that a tefach of space lies beneath it.
- The first case of our Mishnah: one object resting on the ground whose own thickness is a tefach, either a heavy woolen garment or a thick piece of timber. The Mishnah's ruling is that this does not close the split above; the object would have to be genuinely held a tefach clear of the floor.
- The second case: a number of garments stacked in folds, layer over layer. Now the measurement runs from the base of the topmost garment down to the floor. If that distance is a tefach, the top garment counts as elevated by a tefach, and it makes no difference to us that garments rather than air fill the intervening space. Since this is not one single item, the uppermost layer can be treated on its own, and the roof's split is regarded as closed.
- The third case: a man lying beneath the split. Beis Shammai see a person as a single unit, with no top and bottom to be distinguished, so like the thick beam or the heavy garment he closes nothing, having never been lifted a tefach above the floor. Beis Hillel hold that a person has his own s'chach, his upper portion roofing over what is inside him, and that he is therefore reckoned as hollow. Being divisible, he has a tefach beneath his upper part, he is domeh to the stacked garments, and the split overhead is sealed.