Ohalos, Chapter 10, Mishnah 3. This chapter is built around a house whose ceiling contains an aruvah, a hole or skylight in the roof, and it asks how tumah resting inside the house interacts with the airspace directly over that hole. The recurring variable throughout the chapter is the measurement of the aruvah: does the hole open a full tefach square (a posei'ach tefach), or does it fall short of that? Our Mishnah revisits a case that has already come up, this time where the aruvah does not measure a full tefach in each direction, and it presents a dispute among three Tanna'im.
The case
The Mishnah begins: "Miktzas tumah babayis umiktzasa keneged ha'aruvah." A single mass of tumah lies in the house, positioned so that one portion of it sits beneath the solid ceiling while the remaining portion extends beneath the aruvah, the uncovered gap. In this Mishnah, however, the gap does not measure a full tefach in each direction.
On one point all three Tanna'im agree: "habayis tamei." Keilim that are in the house, beneath the roofed area, become tamei. Even though the entire piece of tumah does not sit under the roof (some of it lies under the open aruvah), whatever is under the ceiling is tamei. The dispute concerns keilim held above the aruvah, in the airspace directly over the part of the tumah that is under the opening.
Rebbi Meir
Rebbi Meir rules "ucheneged hatumah tamei." Keilim positioned above the aruvah, which if they looked straight down would face the sliver of tumah lying under the opening, also become tamei. The reasoning is the one we know regarding a single connected piece of tumah: since it is one unit, the tumah travels in both directions, from the portion in the house out to the space of the aruvah, and from the portion under the aruvah into the house. To Rebbi Meir, in this halachah the width of the aruvah makes no difference whatsoever. Whether the opening is a full tefach or less than a tefach, the two parts of the tumah join, and both the house and the space above the aruvah are tamei. That is the meaning of "divrei Rebbi Meir": this is the position of Rebbi Meir.
Rebbi Yehuda
"Rebbi Yehuda omer: habayis tamei ukeneged hatumah tahor." Rebbi Yehuda concedes that the house is tamei: part of the tumah lies under the ceiling, so keilim in the house contract tumah. But keilim above the aruvah remain tahor. His distinction is as follows. Had there been a complete, independent shiur of tumah lying by itself beneath the aruvah, it would rise through the opening even though the opening measures less than a tefach. But here there is no complete piece under the aruvah at all. One portion lies under the opening, the other portion lies under the roof, and the opening is smaller than a tefach. Such tumah does not force its way up through an opening of less than a tefach to render keilim above the aruvah tamei.
The Chazon Ish notes that keilim placed within the airspace of the aruvah itself, directly in line with the tumah, do contract tumah. What Rebbi Yehuda exempts is only what stands higher up, above the opening: tumah of this sort, only a fraction of which sits beneath the gap, will not travel upward through an opening narrower than a tefach.
Rebbi Yosi
Rebbi Yosi replies that the answer depends on the circumstances. The Mishnah has informed us that the mass is split between the covered area and the gap, but it has said nothing about how much sits on either side. Hence: "im yeish batumah k'dei shetechalek vitamei es habayis usetamei keneged hatumah, tamei." If the mass is substantial enough that, upon dividing it, there would be enough tumah to be metamei the house and enough tumah to be metamei the airspace over the aruvah, then everything is tamei. In concrete terms this requires more than a k'zayis: one k'zayis for the section under the gap and one k'zayis for the section under the ceiling. In such a case, a keli suspended over the aruvah contracts tumah even though only a fraction of the mass sits beneath it.
"V'im lav, habayis tamei ukeneged hatumah tahor." Should the mass fall short of that measure, so that splitting it would not yield a k'zayis beneath the ceiling together with a k'zayis beneath the gap, the house is nonetheless tamei, but regarding the airspace above Rebbi Yosi sides with Rebbi Yehuda: a keli suspended over the gap opposite that section of tumah remains tahor. Granted, taken as a single mass there is a k'zayis, yet the section actually resting beneath the gap does not amount to a k'zayis, and tumah in that state does not exit through an opening narrower than a tefach. The halachah is in accordance with Rebbi Yosi.
Reviewing the three views
- Rebbi Meir: the size of the aruvah is irrelevant. The two portions combine, and both the space above the aruvah and the area under the roof are tamei. Even without a k'zayis beneath the opening, its joining with the rest of the piece to form a k'zayis is enough to render keilim above the aruvah tamei.
- Rebbi Yehuda: unless there is an independent piece of tumah beneath the aruvah, the tumah will not shoot up through the opening to be metamei keilim above it.
- Rebbi Yosi: it hinges on the size of the piece. Less than two k'zeisim, so that there is not a full k'zayis for the opening and a full k'zayis for the house, and keilim above the aruvah stay tahor, since the tumah cannot get through an opening that is not posei'ach tefach. Two k'zeisim, and even though it is one piece, the tumah emerges through an opening of less than a tefach and is metamei keilim above the aruvah.
Understanding Rebbi Yehuda
The meforshim invest considerable effort in explaining Rebbi Yehuda's position. The basic idea is this. So long as there is a self-standing piece of tumah under the opening, that tumah has its own status and rises through the aruvah. But once we are forced to rely on the portion lying beneath the ceiling, the entire picture changes, and we view the situation from the perspective of the house: this house is an ohel that contains tumah. Since there is no independent piece of tumah beneath the opening, and whatever lies there is bound up with the tumah under the roof, the governing reality is tumah under a roof, tumah inside an ohel.
Once we begin from tumah situated inside an ohel, the rule is well known. Put the plain question: does tumah in a house escape outward through an opening that is not a posei'ach tefach? The answer is that it does not. That is precisely what Rebbi Yehuda holds. Whenever the portion beneath the gap remains attached to the rest of the mass indoors, what stands before us is nothing more than a house containing tumah, and rendering tamei whatever is outside and above it demands a posei'ach tefach.