Keilim, Chapter 1, Mishnah 5. The chapter is constructed as a set of rising ladders. Already we were given the ten avot hatumah, each rung heavier than the rung below it. Here a second group of ten opens up, counting the impurities whose origin lies inside a human being himself, and once again the order runs from the mildest upward toward the most severe.
One clarification is needed before we begin. Mishnah 5 is not speaking about impurity that a person contracts from something outside of him. A met, for example, is itself an av hatumah, and whoever touches it is rendered impure; there the impurity has been transferred to the person from without. Our list confines itself to the opposite situation: impurity that wells up from within the person's own body, so that he himself is where it begins.
The Mishnah's method is elegant. It follows a single individual who becomes tamei with one form of tumah after another, and at each stage it notes the new restriction or obligation that now falls upon him, which had not applied at the previous, lighter stage.
The heading comes first: "Eser tum'ot" - ten impurities - "porshot min ha'adam," which issue forth from a human being, and the ten are presented in climbing order of weight.
One: Mechusar kippurim
The bottom rung belongs to the "mechusar kippurim," literally one whose atonement is still outstanding. Four people fall into this category: a zav, a zavah, a yoledet and a metzora, each of whom owes korbanot as part of his taharah process and has not yet offered them. Such a person has already gone down to the mikveh and the sun has already set on him, and yet as long as those korbanot remain unbrought, kodashim are closed to him and so is entry into the Beit Hamikdash. The Mishnah's ruling is "asur bakodesh umutar baterumah uvema'aser": the consecrated meat of korbanot is forbidden to him, while terumah (should he be a kohen) and ma'aser sheni are permitted even before the offerings are brought. Once his day has come and he has immersed, those two are already open to him.
Terumah is the share set aside from the produce for the kohanim alone, consumed by a kohen and by the members of his household. Ma'aser sheni is a tenth of the harvest taken off in years one, two, four and five of the Shemittah cycle; it bears sanctity, and the owner eats it himself, but only inside the holy city of Yerushalayim.
Two: Tevul yom
"Chazar lihyot tevul yom" - our man then becomes tamei again, immerses in a mikveh, but nightfall has not yet arrived. Immersion alone does not finish the job; until the sun sets he is not fully tahor, and he is called a tevul yom, one who immersed that day. In this state he is "asur bakodesh uvaterumah umutar bema'aser": barred from kodashim and from terumah, yet still permitted to eat ma'aser sheni. Notice that one restriction has been added to the previous case.
Three: Ba'al keri
"Chazar lihyot ba'al keri" - he then has a seminal emission and becomes tamei on that account. Here the Mishnah says he is "asur bisheloshtan," forbidden in all three: kodashim, terumah and ma'aser sheni. Another rung up the ladder.
Four: Bo'el niddah
"Chazar lihyot bo'el niddah" - our man then cohabits with a niddah and contracts impurity through that. Something entirely new now enters the list: "metamei mishkav tachton ka'elyon." Bedding underneath him receives tumah with the same force by which a zav's impurity reaches an object resting on top of him. Should he press his weight down on a mattress, or on a whole stack of mattresses, each of them turns into a rishon letumah. Until this point his impurity governed nothing beyond his own eating; from this rung onward he begins to pass tumah outward to objects.
Five and Six: The zav
Rungs five and six concern the zav. Zivut means an abnormal discharge produced by illness, and the discharges are counted toward zav status when they occur within a single day or on two successive days. The Mishnah separates the halachot that attach once two such sightings have taken place from the further obligation created by a third.
The Mishnah continues, "chazar lihyot zav" - he becomes a zav - "shera'ah shtei re'iyot," one who has had two sightings. Now "metamei mishkav umoshav": he transmits impurity to a mishkav, an object set aside for lying on, and to a moshav, an object set aside for sitting on, turning each of them into an av hatumah in its own right. Beyond that, "vetzarich bi'at mayim chayim": his taharah calls for immersion specifically in living spring water rather than in an ordinary mikveh. Seven clean days are counted first, and only then does he immerse in flowing spring water; without such water taharah is unavailable to him. At this stage, though, he is "patur min hakorban," with no offering required of him.
"Ra'ah shalosh, chayav bekorban" - a third sighting places upon him an obligation of a korban, two torim or two benei yonah, before his taharah is finished. The tally works the same way whether all three sightings appeared within one day or were spread over three days in a row.
Seven and Eight: The metzora
Rungs seven and eight belong to the metzora. When the relevant marks appear on a person's skin, a kohen inspects them and shuts him away for a week in order to watch what the marks will do. Throughout that week his status is metzora musgar, a quarantined metzora. A second inspection follows: should the marks be unchanged, a further week of quarantine is imposed, and should the second week likewise end with no development, the kohen sets him free. If, however, additional symptoms surface at any stage of the process, or the kohen determines that the tzara'at has spread, the man is declared a metzora muchlat, a confirmed metzora. Impurity attaches to the quarantined man and to the confirmed man alike, yet the stringencies borne by the muchlat are not all laid upon the musgar.
"Chazar lihyot metzora musgar, metamei bevi'ah" - as a quarantined metzora his mere entry transmits impurity: the moment he steps into a house, the people and the vessels present inside are rendered tamei. On the other side of the ledger he is "patur min haperi'ah umin haperimah," released from letting his hair grow long and from rending his clothing. He is equally "patur min hatiglachat umin hatzipporim": at the point when he is pronounced clean, neither the shaving nor the bird service is demanded of him. The usual procedure for a metzora entering taharah is that all the hair of his body comes off and a pair of birds is presented before a kohen, who carries out a prescribed order with them; the Mishnah is teaching that this belongs to the muchlat exclusively. The musgar, when the kohen declares him free of tzara'at, has only to immerse his body and his garments in a mikveh.
"Ve'im haya muchlat" - where his status was that of a confirmed metzora - "chayav bekulan," every one of those obligations rests upon him: his hair grows wild, his clothing is torn, and when he is pronounced clean he shaves and brings the pair of birds as part of becoming tahor. These are rungs seven and eight.
Nine and Ten: A limb severed from a living person
The last two cases deal with a limb detached from a living person. Such a limb, once fully separated, conveys tumah like a corpse, but only if it carries a sufficient amount of flesh. A limb, for these purposes, means the bone together with its flesh and the sinews that belong to it. The bone must be intact; if flesh is missing, whether it still transmits tumah depends on how much is missing, as the Mishnah now explains.
The Mishnah states, "peirash mimenu ever" - a limb has come away from him - "she'ein alav basar kara'ui," carrying less flesh than the required amount. In that case "metamei bemaga uvemasa ve'eino metamei be'ohel": touching it or carrying it brings impurity, while sharing a roof with it does not. "Ve'im yesh alav basar kara'ui" - where the necessary flesh is present - then "metamei bemaga uvemasa uve'ohel": contact, carrying and ohel alike, exactly as with a met.
What amount qualifies as "proper"? The Mishnah defines: "shiur basar kara'ui" - the measure of fitting flesh - is "kedei leha'alot arucha," enough for healing to occur. Picture the limb still attached to the body and ask whether the flesh left on it could have grown and closed over what is missing. Where hardly any flesh survives, no regrowth would have taken place, and the limb ranks as lifeless matter. Where enough remains that the body could have rebuilt the rest and clothed the limb once more, the measure is satisfied and ohel applies as well. Clearly the actual quantity shifts with how large the limb happens to be and with the circumstances of the case.
"Rebbi Yehudah omer" - Rebbi Yehudah supplies a fixed gauge for this capacity to heal: "im yesh bemakom echad" - if at one single spot on the limb there remains flesh - "kedei lehakkifo bechut erev," an amount which, drawn out into a strand as thick as the weft thread of a loom, would reach around the limb's girth - then "yesh bo leha'alot arucha," healing is within reach. In Rebbi Yehudah's understanding, a limb of any dimensions will ultimately recover provided that the flesh still upon it could encircle its own thickness by that measure.
So the Mishnah has walked one man up ten rungs. He begins as someone whose only limitation touches what he may eat, and he ends at the level of a corpse itself: from the mechusar kippurim who may still eat terumah, to bedding and seats made avot hatumah, to tumah conveyed simply by walking through a doorway, to a severed limb that spreads impurity to everything under one roof with it. Each stage adds a stringency the previous one did not carry, and read in order the list becomes a map of how tumah tightens its hold step by step.