Negaim, Chapter 5, Mishnah 1. Our mishnah deals with one of the simanei tumah of a nega, the se'ar lavan, two hairs inside the white patch that have turned white, and with the question of sequence: did the bahares appear first, or did the white hair come first? Before we open the words of the mishnah, there is a Gemara that belongs right beside it, because this very halachah was once debated in shamayim.
When the Yeshiva Shel Ma'alah Was Divided
The Gemara in Bava Metzia 86a, in perek HaSocher es HaPoalim, tells about Rabbah bar Nachmani, the stepfather and rebbe of Abaye. Informers denounced him to the Persian authorities, he fell out of favor with the government, and he was forced to flee. He moved from place to place while his pursuers, who wanted his life, closed in on him. He sat down by the water, beside the fence around a palm tree, and he learned.
At that same hour, in the mesivta derakiya, the academy on high, a question was under debate. The halachah in its plain form was never in doubt: should the bahares have shown itself first and the hair whitened only afterward, the man bears tumah; should the whitened hair have already been standing there before the bahares surfaced, he remains tahor. What they were weighing was the doubtful case, where nobody can establish the order. Hakadosh Baruch Hu, kevayachol, held that such a man is tahor. Ranged against that view stood the entire heavenly yeshiva, the malachim together with the chachamim of the generations that had passed on, all of them holding tamei.
The question then arose, "Man nochach?" Who is able to bring this to a resolution? The response was that Rabbah bar Nachmani should be the one to rule, since he had testified about himself, "ani yachid benega'im," that in the halachos of nega'im no one matched him, and "ani yachid be'oholos," that in the halachos of oholos too he had no peer.
An emissary was dispatched to fetch him, yet the Malach Hamaves was unable to draw near, since Torah did not stop issuing from his lips for even a moment. The Gemara describes something similar with Dovid Hamelech, whose learning shielded him from the Malach Hamaves until his attention was diverted and the opening was created. Here, a gust of wind set the reeds rattling. Rabbah bar Nachmani took the noise for Persian cavalry bearing down on him, and he cried out that he would rather his soul be taken than that he fall into the hands of the government. As his neshamah was departing, shamayim posed the question to him, the doubtful case of the order between the bahares and the se'ar lavan, and his reply was, "Tahor, tahor."
A heavenly voice rang out over him: "Ashrecha, Rabbah bar Nachmani," praiseworthy are you, "shegufcha tahor veyatz'ah nishmascha betahor," for your body is pure and your soul went out with the word tahor. And in Pumbedisa, his own city, a slip of paper came fluttering down from above with the message "nisbakesh biyeshiva shel ma'alah": Rabbah bar Nachmani has been called to the academy above.
The mishnah
Now to the language of the mishnah itself. "Bahares kechatzi gris": someone is carrying a white patch that measures only half a gris, "ve'ein bah kelum," and it contains nothing whatsoever, not a single siman tumah. "Noldah bahares kechatzi gris": afterward a further half-gris of bahares breaks out, so that the patch now reaches a full gris, the minimum measure for a nega, "uva bah shtei se'aros," and within it two hairs appear, two black hairs that have turned white. "Harei zu lehachlit": we declare him a metzora muchlat outright. A complete gris of bahares was standing there before those hairs whitened, so the se'ar lavan counts as a genuine siman tumah, and no period of hesger is called for.
The mishnah then supplies its own justification: "she'amru," for the chachamim taught, "im bahares kadmah lise'ar lavan tamei," that a bahares which arrived ahead of the whitened hair renders him tamei, and "ve'im se'ar lavan kodem labahares tahor," that hair which whitened before the bahares emerged leaves him tahor. "Safek, tamei": where the sequence cannot be established, the Tanna Kamma holds him tamei.
Lo bashamayim hee
The Rambam paskens like the Tanna Kamma of our mishnah, that the safek is tamei. In other words, he rules against the ruling of Hakadosh Baruch Hu in that Gemara and against Rabbah bar Nachmani, and together with the mesivta of shamayim, because the Rabbanan of the time of the mishnah paskened tamei. And that is the rule: heaven does not decide these questions. Halachah is determined by the chachamim, by the majority of the chachamim of a given time, who establish what is assur and what is muttar.
The well known case is the tanur shel Achnai, in Bava Metzia 59b. There Hakadosh Baruch Hu sided with Rebbe Eliezer ben Hyrcanus in holding that oven tahor, and Rebbe Yehoshua ben Chananya countered with the words "lo bashamayim hee": Torah is not kept above anymore, it was handed over to us down here, and Torah's own directive, "acharei rabbim lehatos," tells us to go after the majority of chachamim. The Gemara goes on to relate that one of the chachamim afterward encountered Eliyahu Hanavi and inquired how Hakadosh Baruch Hu had reacted in that moment when Rebbe Yehoshua declared lo bashamayim hee. Eliyahu replied that He smiled and said, "nitzchuni banai, nitzchuni banai," repeating twice that His sons had bested Him.
Rabbi Yehoshua keihah
Three words bring the mishnah to a close: "VeRabbi Yehoshua keihah." Rabbi Yehoshua's teeth were set on edge by this halachah. The verdict of tamei in a case of doubt sat badly with him, yet he offered no definite alternative of his own, and the reason for his discomfort is plain: throughout the halachos of nega'im the accepted principle runs in the opposite direction, that a doubtful case leaves a person tahor. This case alone is the exception, where uncertainty about the sequence of the bahares and the white hair still leaves the man tamei. That is the halachah we follow, even though the very same question was once contested in the academy of shamayim.