Niddah, Chapter 4, Mishnah 7. This mishnah continues the chapter's discussion of a woman in difficult labor, a makashah, whose childbirth is accompanied by pain. Blood that comes together with such pains is not treated as ordinary blood; it belongs to the category of blood of childbirth. Here, however, the case is more intricate: the pains are the pains of a miscarriage, and they come while the woman is still inside the days of purity that followed an earlier birth.
The case
"Hamakashah besoch shemonim shel nekeivah." A woman gave birth to a baby girl, and the Torah grants her eighty days following such a birth during which blood that she sees is dam tohar, pure blood. Within those eighty days she becomes pregnant again, and now she is in labor pains connected with the loss of that new pregnancy. What is the status of the blood she sees during those pains?
The mishnah rules: "kol damim shehi ro'ah tehorim ad sheyeitzei havlad" - all the blood she sees is pure until the new fetus emerges. She is still inside the eighty days of the daughter she bore earlier, and those days of purity continue to govern her blood, including the blood that accompanies these labor pains, right up to the moment the new fetus comes out.
Rabbi Eliezer disagrees
"Rabbi Eliezer metamei." Rabbi Eliezer holds that this blood is not pure. In his view, blood that comes with the pains of delivering this second child is not covered by the purity of the first birth at all. It stands on its own and carries the status of blood that renders her tamei.
The kal vachomer of the Chachamim
The Chachamim countered Rabbi Eliezer with an a fortiori argument, a kal vachomer. The mishnah records it in two balanced halves. The opening half: "Umah bimkom shehechmir", in a setting where the halacha took a stringent stance, "bedam hashofi", with respect to blood seen while no pain is present, it nevertheless ruled leniently, "heikel bedam hakoshi", with respect to blood that comes along with the pains. The closing half draws the conclusion: "makom sheheikel", in a setting where the halacha is already lenient "bedam hashofi", "eino din", is it not only right, "sheneikel bedam hakoshi", that we rule leniently about the blood of the pains?
Their argument runs as follows. In the ordinary case of a woman approaching childbirth, the halacha is strict with dam shofi, the blood she sees during the quiet intervals when she is not in pain, and yet it is lenient with dam hakoshi, the blood that comes together with the labor pains themselves. Now consider our woman: she is inside the eighty days, so even her dam shofi is pure, it is dam tohar. If in a situation where dam shofi is treated strictly the blood of the pains is nevertheless treated leniently, then surely in a situation where even dam shofi is already pure, the blood of the pains should be pure as well. It is a strong and elegant argument.
Rabbi Eliezer's response: dayo
Rabbi Eliezer's answer opens with "Amar lahen", he said to them. He does not attack their reasoning; he limits how far it can reach: "Dayo lavo min hadin", a halacha that arrives through such reasoning need go no further, "lihyos kanidon", than the case that served as its starting point. He then presses them with a question: "Mimeh heikel aleha?" Where precisely did the leniency you are invoking come from? And he supplies the answer: "Mitumas zivah". In that original case the woman stood in her days of zivah, and the entire leniency amounted to this, that blood accompanying her pains would not make her a zavah. "Aval temei'ah tumas niddah", yet with regard to the tumah of niddah she remains tamei.
In other words, the kal vachomer can transfer only the leniency that existed at its source, and that leniency reached no further than tumas zivah. It therefore cannot purify our woman completely. According to Rabbi Eliezer, then, the blood she sees with these labor pains within the eighty days leaves her with tumas niddah.
Our mishnah thus preserves both the ruling and the debate behind it: the accepted position that the days of purity following the birth of a daughter govern all the blood she sees until the new fetus emerges, and Rabbi Eliezer's insistence that a kal vachomer, however compelling, may carry a leniency only as far as its own source allows.