Negaim, Chapter 13, Mishnah 12. Until now the chapter has dealt largely with a bayis hamenuga, the house that is itself afflicted, and with people and objects that enter it. This mishnah turns the picture around. Here the house is perfectly tahor, and it is the person who is the source of tumah: a metzora walks in. The metzora conveys tumah not only by touch but by his very presence, and the mishnah asks how far that presence reaches.
How high does his tumah rise?
"Metzora shenichnas labayis": a metzora comes inside a house. "Kol hakeilim sheyeish shom temeiyim": whatever vessels are found there contract tumah, and the mishnah adds, "afilu ad hakoros," even ones resting as high as the beams. The reference is to the utensils and furnishings already sitting in the house, and the ruling is that his tumah saturates the whole airspace, from ground level up to the rafters.
"Rebbe Shimon omer": Rebbe Shimon disagrees, holding "ad arba amos," that the tumah extends upward only four amos. As the Rav explains it, whatever lies above four amos counts as a domain of its own, territory in which the metzora is simply not situated, so nothing of his tumah arrives there. And why is four the number? A typical man stands three amos tall, and the mishnah adds "ve'amah achas lifshot yodayim veraglayim," a further amah allowing for the space he takes up when he extends his arms and legs. Together those measurements mark out his own domain; past its upper limit his tumah accomplishes nothing.
A word about the measurement itself. An amah is generally reckoned somewhere between a foot and a half, that is eighteen inches, and two feet. Three amos would therefore not describe a man of six feet, but at the shorter reckoning it comes out to something in the neighborhood of five and a half feet, which is quite plausible for average height in earlier generations, when people were generally shorter than today.
The mishnah closes the dispute with "ve'ein halacha keRebbe Shimon." His limitation was not accepted; we rule instead like the opening view, that whatever stands in the house is rendered tamei, right up to the beams overhead.
"Keilim miyad temeiyim"
The mishnah continues: "keilim miyad temeiyim," the vessels are tamei immediately. The straightforward reading is that this refers to the very same vessels just discussed, namely those in the house, and it tells us that no waiting period is required: the moment the metzora enters, they are tamei.
The Rav reads the phrase differently. He takes it as speaking of the keilim that contract tumah "ad hakoros" in the view of the first tanna, and within four amos according to Rebbe Shimon, and he appends the words "keshenichnas imohem labayis hamenuga," meaning that the metzora came into the afflicted house together with those vessels. The Tosefos Yom Tov shows that such a reading cannot be maintained: the Rav has fused two separate approaches and thereby contradicted himself. Our mishnah speaks of vessels already positioned inside the house rather than ones the metzora brought along, and the house in question is not afflicted in the first place. The comment makes no sense on its own terms, and the Tosefos Yom Tov therefore rules that the Rav's language here is mistaken.
Rebbe Yehuda and the time to light a lamp
The claim that the vessels inside are tamei at once does not go unchallenged. "Rebbe Yehuda omer": Rebbe Yehuda maintains that they are affected only "im shoha kedei hadlokas haneir," if the metzora lingered inside for as long as it takes to kindle a lamp.
The Rav's treatment of this measure is remarkable. Rebbe Yehuda is not arguing across the board. Should the metzora have come in birshus, at the householder's invitation, Rebbe Yehuda agrees that the vessels are tamei at once. His position addresses only the case of one who walked in unbidden. The tumah at issue operates through the metzora's moshav, the spot where he settles, and it is a settled presence that transmits it. An invited guest acquires a moshav the moment he halts inside, since his being there enjoys the consent of the one who lives there. An uninvited entrant, by contrast, has no moshav at all, unless he remains long enough for a lamp to be lit.
Why should that particular span of time create a moshav? Because if the metzora stood there that long and the owner did not eject him, his remaining there has become an accepted presence, and he has acquired a moshav. If he was not there even that long, no moshav has been established, and the owner's failure to remove him proves nothing: he was simply preoccupied with lighting the lamp. The mishnah is picturing the hour of bein hashmoshos, when it has grown dark inside the house, whether it is erev Shabbos and he is kindling the Shabbos lights, or an ordinary weekday and he is lighting the lamps that illuminate the house as the daylight fades. Being busy with the lamp, he cannot throw the metzora out just yet, but the instant he finishes he will. Only if the metzora outlasts that interval has his presence become a moshav that conveys tumah.
The Rav offers no verdict at this point, though we may assume that we follow the tanna kamma: the moment the metzora steps inside, the utensils standing there are already tamei.