Mishnah 11 is the final mishnah of the chapter, and the last of the four cases in which Beis Hillel retracted and ruled like Beis Shammai. Its subject is the transmission of tumah by means of an ohel (a covering), and it appears in a simpler form in Maseches Keilim (chapter 9, mishnah 2). Let us first lay out the background and present the subject of the mishnah from the outside, as we have done with the previous mishnayos, and afterward return to its own wording.
Four categories of things that can contract tumah:
Adam - human beings.
Keilim - vessels.
Ochlin - food.
Mashkin - liquids.
The seven raw materials from which vessels are made:
Beged - woven cloth.
Sak - goat hair.
Metal.
Or - animal hides.
Etzem - the hard materials of animals, such as bones and hooves.
Wood.
The first six materials are collectively called kelei shetef, because vessels made from them can be immersed in a mikvah in order to become pure. The seventh material is earthenware - fired clay - and it differs from the others: it is not considered a kli shetef, since it cannot go into a mikvah. This means that once an earthenware vessel has become tamei, there is no longer any way to purify it.
The unique nature of earthenware:
Another interesting feature of earthenware: unlike the other vessels, it does not become tamei through direct contact with the source of tumah. A wooden or metal cup that a dead mouse touched becomes tamei, whereas if the dead mouse is only suspended in the airspace inside it, the cup remains pure. With earthenware the rule is the reverse: the outer surface does not contract tumah, so if a dead mouse touched the outer wall of an earthenware cup, the cup remains pure; but if it was suspended within the airspace inside it, the vessel becomes tamei. It emerges that an earthenware vessel contracts tumah through the airspace within it.
"Tzamid pasil":
The Torah sets out a special law regarding an earthenware vessel that is tightly sealed, known as "tzamid pasil". 'Pasil' means a seal or covering, and 'tzamid' means tightly fastened. That is, if the mouth of the earthenware cup was sealed with clay or a similar substance, so that there is no access to the airspace within it, tumah has no way of entering it.
One of the seven ways in which tumah is transmitted is called ohel: being under one roof together with a corpse or with a significant part of one. Everything under that roof becomes tamei, including wooden and metal vessels. But an earthenware vessel sealed with a tzamid pasil does not become tamei through an ohel, and moreover, even its contents are protected from tumah. If a sealed earthenware cup contains coffee, the coffee remains pure; and if a sewing thimble is lying inside it, the thimble remains pure.
This protection is stated on one condition: that both the vessel itself and the seal covering it be pure. But if the vessel is tamei to begin with, the tumah of the ohel passes through it as though it were not there at all.
The purification process:
Something that became tamei is generally purified by immersion in a mikvah, and at nightfall it is tahor. One important exception is tumah from a corpse: a vessel that contracted tumah from a corpse - whether by touch, by carrying, or by being under the same roof - is not helped by a mikvah alone. It must first be sprinkled with the waters of the Red Heifer on the third day and on the seventh day, and only afterward immersed in a mikvah.
Chaverim and amei ha'aretz:
Chazal divided the world into two categories of people: chaverim and amei ha'aretz. A 'chaver' is a member of the fellowship, someone who formally commits to living by the stringent rules of tumah and taharah; anyone who has not accepted this commitment upon himself is considered an am ha'aretz. Since an am ha'aretz is not necessarily well versed in the ways of tumah and taharah, the Sages treated him rabbinically as an av hatumah, and the chaver assumes that everything belonging to an am ha'aretz - his foods, his drinks and his vessels - is tamei.
For this reason a chaver's contact with his am ha'aretz neighbor is limited: he will never eat a meal with him and never share food with him. Vessels, however, they did share with one another, apparently because vessels were in short supply. If the wife of a chaver needed a thimble for sewing, she would borrow it from her neighbor, the wife of an am ha'aretz, immerse it in a mikvah, and it was tahor.
It is worth emphasizing: amei ha'aretz are considered tamei not because they are suspected of dishonesty or bad intentions, but because they are not sufficiently knowledgeable in the halachos to be relied upon. Their word, however, is believed. Therefore, when the wife of a chaver borrows a thimble from her neighbor, she relies on her: if the neighbor tells her that the thimble contracted tumah from a corpse, she will know that a mikvah does not suffice and that a full purification process is needed; and if she says nothing, she will assume that immersion in a mikvah is enough.
The case in the Mishnah:
The wife of an am ha'aretz is careful to keep her cup in a state of taharah, and she wants to keep a thimble tahor for her neighbor. So she places the thimble inside the cup and seals the cup with a tightly sealed lid. Now, even though someone died in the house and everything in it became tamei through being under the same roof, she believes that the sealed earthenware cup protected its contents, that the thimble inside it is tahor, and she will happily lend it to her neighbor the chaverah.
But here lies the problem: since the Sages said that everything belonging to an am ha'aretz is presumed tamei, the earthenware cup itself is tamei, at least rabbinically. And a tamei vessel does not form a barrier - even though it has a tightly sealed lid, it does not protect its contents from the tumah of being under the same roof. The result is that by Torah law, and according to the best intentions of the am ha'aretz's wife, the thimble is tahor; but in practice, rabbinically, it is tamei, and tamei from a corpse.
And since the wife of the am ha'aretz does not know this, she will not inform her neighbor that the thimble is tamei. The neighbor, the chaverah, will indeed assume that the thimble is tamei as any vessel of an am ha'aretz is, but she will think that immersion in a mikvah suffices for it, and it will never occur to her that it requires sprinkling on the third day and on the seventh day. She ends up failing in her guarding of taharah.
The conclusion of the Sages:
Therefore the Sages said: an earthenware vessel with a tightly sealed lid does save food, drink and even an earthenware vessel inside it, because there is no concern of a stumbling block there - the am ha'aretz will act as he always does, a chaver will in any case never take food or drink from him, and a tamei earthenware vessel is not lent out. But regarding a rinsable vessel, such as a metal thimble, which people do lend to one another - we will protect the chaverim and rule that a thimble inside a sealed earthenware vessel is tamei in any case, and that a sealed earthenware vessel does not save from the spread of tumah.
Let us return to the wording of the Mishnah:
"Kli cheres matzil al hakol k'divrei Beis Hillel" - the initial position of Beis Hillel: a sealed earthenware vessel protects everything inside it from the tumah of an ohel, even when a corpse lies in the same room, provided that the cup and its seal are themselves tahor.
"U'Veis Shammai omrim: eino matzil ela al ha'ochlin v'al hamashkin v'al klei cheres" - Beis Shammai limit this protection to the food and drink inside the sealed vessel, and to another earthenware vessel lying within it, concerning which we may likewise assume that it can remain tahor, since in any case a chaver does not borrow such items. A metal thimble, however, we assume is tamei.
"Amru lahem Beis Hillel: mipnei mah?" - the Torah established that a sealed earthenware vessel forms a barrier against tumah, so why should you say that the thimble is tamei?
"Amru lahem Beis Shammai: mipnei shehu tamei al gav am ha'aretz, v'ein kli tamei chotzetz" - we are dealing with the cup of an am ha'aretz, and that cup is tamei, and a vessel that is itself tamei does not form a barrier against the spread of tumah. It turns out that the thimble has become tamei, while the am ha'aretz believes it is tahor and lends it to his neighbor.
"Amru lahem Beis Hillel: v'lo tiharatem ochlin u'mashkin shebesocho?" - how can you say that the sealed earthenware vessel protects the food and drink inside it from becoming tamei, yet does not protect a metal thimble? The two positions do not sit together.
"Amru lahem Beis Shammai: k'shetiharnu ochlin u'mashkin shebesocho - l'atzmo tiharnu" - when we ruled that the food and drink inside the earthenware vessel are tahor, we ruled so for the am ha'aretz alone. After all, who is going to eat that food and drink that beverage? The am ha'aretz himself, and he will act as he always does. A chaver will neither eat nor drink of them, so we have no concern that he will stumble.
"Aval k'shetetaher es hakli - tiharta lecha v'lo" - but when we declare that a kli shetef (a vessel that is purified by immersion in a mikvah) lying inside the sealed earthenware vessel is tahor, while in truth it may well be tamei, since the earthenware vessel itself is presumed tamei - this is not a ruling of taharah for him alone, for the am ha'aretz, but for you as well, for the chaver. In other words, the entire purpose of the decree is to protect the chaver from coming to grief, lest he think the vessel is tahor when in fact it is tamei, or think that immersion in a mikvah suffices when in fact it carries the tumah of a corpse.
Therefore, in order to protect the chaverim, it was established that an earthenware vessel does not protect a kli shetef inside it - a vessel whose normal purification is immersion in a mikvah - lest a chaver stumble through it. And this rule was stated for all vessels, whether the vessels of an am ha'aretz or the vessels of a chaver, for if the vessels of a chaver were governed by a different rule, the am ha'aretz would learn from him and err. True, we assume that the amei ha'aretz have learned certain things and know a fair amount, but not enough, and a little knowledge can be dangerous. For this reason the rule was stated across the board: all earthenware vessels, by rabbinic law, even when sealed with a tight-fitting lid, do not protect their contents when those contents are a kli shetef.
"V'chazru Beis Hillel l'horos k'divrei Beis Shammai" - Beis Hillel accepted the argument that the chaverim must be protected, changed their position, and ruled like Beis Shammai: an earthenware vessel sealed with a tight-fitting lid does not protect, by rabbinic law, a vessel inside it from the tumah of a corpse in an ohel, when that vessel is a kli shetef, lest a chaver borrow it and content himself with immersion in a mikvah, not knowing that it requires the full seven-day purification process with the waters of the red heifer.
In summary: in this Mishnah we examined the laws of earthenware vessels - that such a vessel is not a kli shetef and is not purified in a mikvah, and that it becomes tamei through its inner airspace rather than by external contact - and the power of a tight-fitting lid to save its contents from the tumah of an ohel, provided that the vessel and its seal are tahor. We saw the distinction our Sages drew between chaverim and amei ha'aretz, and the assumption that everything belonging to an am ha'aretz is presumed tamei, and from this the stumbling block liable to be placed before a chaver who borrows a vessel taken from a sealed cup. Beis Shammai limited the protection to food, drink and earthenware vessels alone, and Beis Hillel, recognizing the need to protect the chaverim from stumbling, reversed themselves and ruled as Beis Shammai did - and this is the last of the four cases in this chapter in which Beis Hillel came to rule like Beis Shammai.