Ohalos, Chapter 15, Mishnah 2. Our Mishnah continues to examine when a flat surface raised off the ground counts as an ohel that carries tumah, and when we are dealing with two independent ohalim that simply happen to touch. The Mishnah presents two pictures: wooden boards that meet one another at their corners, and a table built on a box-like base.
Two boards meeting at the corners
The Mishnah's opening words are "tavlaos shel eitz", panels of wood, which "she'no'agos zo bi'zo be'karnosayhen", make contact with one another at their corners. To visualize the arrangement, think of a chessboard and pick out two black squares whose corners meet at a single point. That is precisely the layout under discussion.
Each panel is then described as "vehen gevohos min ha'aretz", elevated above the ground below it, by the measure of "be'fosei'ach tefach", and each panel itself measures a tefach in length and a tefach in width. The rule is that any flat covering of one tefach in each direction, held a tefach above the ground, constitutes an ohel. Every one of these panels therefore qualifies as an ohel on its own terms.
That sets up the question. Since the two boards are in contact, do we look at them as one large ohel, or do we look at them as two separate ohalim that merely brush against each other?
The Mishnah gives us the case: "tumah tachas achas meihen", there is tumah, a kezayis min ha'meis, underneath one of the two boards. Now someone touches the other board, "ha'nogei'a ba'shniyah", the second one, the board that has nothing at all beneath it. The Mishnah rules: "tomei tumas shiv'ah", he is tomei for seven days.
Should we conclude from this ruling that the pair has fused into a single tent? Not at all. For two coverings to be reckoned as one ohel, the area they share where they come together would have to measure a full tefach in each direction, and corners meeting at a single point offer nothing approaching that. In halachah they remain two independent ohalim.
If so, why is a person who touched the second board tomei for a full seven days, when the meis is not under that board at all?
The explanation rests on the principle of cherev harei hu k'chalal, that an implement in contact with a corpse takes on the full severity of the corpse itself. The lower panel is stretched over the meis as its tent, which raises it to the rank of avi avos ha'tumah. The second panel is in contact with an object holding that rank, so it acquires the very same rank. Nothing more than contact is required; no shared tent is needed for this. Accordingly, the man who laid his hand on the second panel has handled an avi avos ha'tumah. He becomes an av ha'tumah, and one in that state remains tomei a full week and requires hazayah, the sprinkling of water containing ashes of a parah adumah.
That contact with the first panel produces a week-long tumah requires no teaching at all. What the Mishnah comes to reveal is that the second panel brings about exactly the same result, even though it never combines with the first into one tent.
The Bartenura's question: why isn't this the third link?
At this point a genuine difficulty presents itself, and the Bartenura poses it. In the opening perek of our mesechta we studied a series of transmissions: an implement in contact with a corpse is tomei for a week, and a second implement in contact with that first one is likewise tomei for a week. At the third stage of the series, however, be it a human being or a vessel that comes into contact with the vessel which touched the vessel that had touched a corpse, the tumah lasts only until nightfall and not for seven days.
By that count, our case should come out differently. There is a meis; board number one becomes tomei; board number two touches board number one; and I touch board number two. That would make me the third in line, and I should be tomei only until the evening, not for seven days.
The Bartenura's response is brief: "ein ha'ohel mis'chasheiv", a tent is left out of the reckoning. Suppose the lower panel had done nothing more than make contact with the corpse, and the other panel then made contact with it, and my hand then reached that other panel: in such a chain my tumah would indeed lapse at nightfall. But the lower panel is far more than a piece of wood that came into contact with a corpse. It serves as the tent spread over the meis, and a tent is never assigned a rung on the ladder of transmission. So when the other panel touches it, the halachah views that as contact with the corpse directly. I stand second in the series rather than third, and whoever stands second is tomei for a week.
Keilim beneath each board
The Mishnah proceeds: "keilim she'tachas ha'rishonah temei'im", vessels lying beneath the first panel, the one spread over the corpse, contract tumah, since they share the very tent space in which the meis is found.
"Ve'she'tachas ha'shniyah tehorim", but keilim lying under the second board, the one that touches the first only at its corner, remain tahor. Since the two boards are not one large ohel, those keilim were never inside the ohel ha'meis at all.
The table and its base
The Mishnah now turns to a table, and to picture it we have to crawl underneath. First, how the table is built. Take a wooden box with four walls, open at the top and open at the bottom, so that it goes right through. Set a wide, flat board on top of it. The board is broad enough that on every side it juts out past the walls of the box by a tefach. Crawl under the table, look up, and you see a tefach of overhanging board; move to the other side and you see the same; and so on all four sides.
The four-walled box is called a ribu'a, and its interior is an ohel in its own right. Tumah inside the box makes any keli inside the box tomei, but it does not reach out beyond the walls, not even to the space under the tabletop and not even to the space under the protruding rim. That space belongs to a different ohel.
The question of the Mishnah is the reverse: what about tumah under the tabletop, outside the box?
"Hashulchan eino meivi es ha'tumah", the table does not convey the tumah, meaning that it does not carry it horizontally through the area beneath it, "ad she'yehei bo ribu'a", unless the top projects past its base, the ribu'a, by the measure of "be'fosei'ach tefach", a full tefach. That is how the Bartenura reads the phrase. We are therefore looking at a pair of tents: the hollow of the box, and the strip of space under the projecting edge. Had the top not extended a tefach past the box, only one tent would exist here, the ribu'a itself; tumah under the edge would rise straight upward and descend straight downward, but it would not move laterally.
The Mishnah Achronah explains what qualifies the base as a tent in its own right: it stands open above and open below. A sealed box would be a receptacle capable of receiving tumah, and an object of that sort cannot serve as a partition to block tumah. This frame, however, being open right through, does not receive tumah, and it is also not fastened to the board above it. It emerges on its own, then, as a separate ohel.
Reviewing the Mishnah
Two panels of wood, arranged like a pair of black squares on a chessboard, meet only where their corners come together. Each measures one tefach in length and one in width, and each stands a tefach above the ground. They do not form one enlarged tent, since the area they share at the point of contact falls vastly short of the needed tefach in each direction; each one is a tent by itself.
Even so, when the corpse lies beneath one of the panels and a person makes contact with the other, he contracts a week-long tumah. The reason is not any merging of the two tents. Rather, the panel spread over the meis holds the rank of avi avos ha'tumah; through cherev harei hu k'chalal the panel touching it acquires that identical rank; and whoever touches that panel becomes an av ha'tumah, whose tumah lasts a full week.
Keilim under the first board, the one over the meis, are tomei. Keilim under the second board are tahor, since they were never under the ohel ha'meis.
And in the second case: a box open at top and bottom with a wide board laid over it. The interior of the box is one ohel, and if the board projects a tefach beyond the box on its sides, the space beneath the overhang is a second ohel. Tumah under the overhang spreads sideways beneath the table but does not enter the box, and tumah inside the box does not come out, because each is an ohel unto itself.