Ohalos, Chapter 8, Mishnah 3. This chapter sorts objects into categories: some serve as an ohel that carries tumah from one place to another, some serve as a chatzitza that blocks tumah from passing, some do both, and some do neither. Our mishnah presents the group that goes only one way: "Eilu mevi'in velo chotzitzin", these bring the tumah but do not block it. And here is the striking part: nearly every item on this list already appeared as an item that does block tumah. The objects are the same; only the circumstances have changed.
Chests and baskets without a proper bottom
The mishnah begins: "hashida vehateiva vehamigdal". A shida is a large wooden chest. A teiva is the box of the shulchani, the money changer. A migdal literally means a tower, and here it refers to a standing storage cabinet. The mishnah continues: "kaveres hakash", a basket woven of straw, "kaveres hakonim", a basket woven of reeds, and "bor sfina Aleksandris", the water tank built into the great Alexandrian ships to hold the drinking water for the voyage.
Each of these containers appears in another mishnah among the objects that do serve as a barrier. So what changed? The mishnah spells out the two disqualifications: "she'ein lahem shulayim", that they lack a flat base, their underside being curved instead, and "ve'einan machzikim arba'im se'ah", that their volume falls short of forty se'ah "belach", measured in liquid, "shehem korayim beyovesh", a quantity equal to two kor of dry goods.
To understand why this matters, we have to remember why such a container is not mekabel tumah in the first place. A vessel of this size cannot be carried when it is full. It is simply too heavy, and if you attempted to move it loaded, it would come apart. A vessel that cannot be moved when full is not treated as a vessel at all for tumah, and therefore it can stand as a chatzitza. But if the bottom is rounded, you can shift it and roll it along even when it is full. And if it does not hold forty se'ah of liquid (two kor of dry produce), it is small enough to be picked up while loaded. In either case it is a genuine keli, it is mekabel tumah, and once something is capable of receiving tumah it can no longer block tumah.
The two features have to be present together. Should the vessel hold less than forty se'ah of liquid, that is, two kor of dry produce, a perfectly flat base will not help it: it remains susceptible to tumah. And should its underside be curved, its sheer size will not help it either. The exemption belongs only to a container that is both flat based and large, for about such a vessel we can say that a person cannot budge it while it is loaded, that it would fall apart if he tried, and that it therefore never enters the category of a keli that receives tumah. Missing one of the two features, it is susceptible, and susceptibility rules out blocking, since nothing that can catch tumah is able to stop it.
Coverings that were not made into a tent
The list then moves on to fabrics and coverings: "vehayeri'ah", a curtain; "vehaskartya", a leather apron; "vehaktavla", a leather spread; "vehasadin", a sheet of cloth; "vehamapatz", a mat woven from soft, bendable reeds; and "vehamachatzeles", a mat woven from hard reeds. All six of these show up as well in the roster of items that hold tumah back. What disqualifies them here?
The mishnah supplies the reason itself: "she'ein asuyin ohel", no tent was made out of them. Erected as a tent, with both sides and covering formed from the material, any one of them does serve as a barrier. In our case it was simply laid out flat. The Bartenura sketches the situation: a roof has an opening in it, and someone draws one of these coverings across the roof above, the way a person stretches out a tarpaulin.
One might object: in that scenario there are walls and there is a roof, so why is this not an ohel that blocks? The answer is that the walls are not produced by the covering. Only the roof comes from the sheet or the mat; the walls belong to the house. For these materials to form an ohel that holds tumah back, the entire tent, walls and roof alike, must be made of them.
Animals that have died
The mishnah turns next to living creatures: "uvheimah vechayah shemeisu", domesticated beasts and wild animals that have died. Cattle and wild animals pressed close together in the required manner constitute an ohel, and as long as they are alive such a cluster both conveys tumah and stops it. That dual role depends entirely on their being alive. Once they are dead they still form a covering that conveys the tumah, but they have lost the power to hold it back.
Why should death make the difference? An animal that expired on its own is a neveila, and a neveila is tamei in itself, so it plainly cannot serve as a barrier, since nothing tamei ever does. But take a kosher animal that a qualified shochet slaughtered properly, where no neveila is involved at all. Even there, blood drains out of the carcass, and dam belongs to the group of seven mashkin, those liquids whose contact makes food capable of receiving tumah. And food that one of those liquids has touched, though it has not yet turned tamei, has already forfeited its standing as a barrier against tumah.
Food that is susceptible
The mishnah adds "v'ochalim tmeiyin". This is not restricted to food that actually contracted tumah. As explained, it includes food that was huchshar lekabel tumah, food that came into contact with one of the shiv'ah mashkin. From that moment it is too late: such food will not stand as a chatzitza against tumah. Once it is fit to receive tumah, it does not block tumah.
The pattern of the mishnah
Every item until now was already taught in the previous mishnah among the things that do block tumah. Only the case has changed:
- The earlier mishnah dealt with the shida, the teiva, the migdal, the straw kaveres, the reed kaveres and the water tank of the Alexandrian ship in the condition of having a flat base along with the necessary volume. Our mishnah takes up those same six when one of the two features is absent.
- The earlier mishnah dealt with the yeri'ah, skartya, ktavla, sadin, mapatz and machatzeles after they had been set up as a tent. Here no tent was fashioned out of them, so they do not block, not even when spread across an opening in a roof, since an ohel that stops tumah needs its sides no less than its covering to come from the material itself.
- The earlier mishnah dealt with beheimah vechayah while alive: bunched together properly, such animals both carry tumah and stop it. Ours speaks of them after death, when they carry and no longer stop.
- The earlier mishnah dealt with ochalim tehorim, food that never met one of the seven liquids. Ours speaks of food that did meet one of them, so that even before it is actually tamei it has become capable of becoming tamei.
Musaf aleihem: the hand mill
The closing entry has no counterpart in the earlier list; it was never raised there at all. That is precisely why the mishnah prefaces it with "musaf aleihem", an addition to everything that came before: "harechayim shel adam". The reference is to a millstone worked by hand, the small sort that a person turns himself, in contrast to the heavy mills powered by water or pulled by an animal. A mill of that kind carries the status of a keli, and being a keli is exactly what limits it: it can spread over whatever lies beneath and deliver tumah there, yet it will never seal the tumah off.
The thread running through the entire mishnah is a single principle: whatever is itself susceptible to tumah cannot stand in tumah's way. A container light enough to be carried when full, food already made fit to receive tumah, a carcass or the blood that flows from a slaughtered animal, a hand mill that is a vessel in its own right: each of them can form a covering that carries tumah downward, but none of them can form a barrier that stops it.