The mishnah before us is the longest mishnah in all of Shas - three hundred and nineteen words, which tells us that we have a great deal of material ahead. Its subject is the status of a part that has separated from a limb severed from a living person.
All agree that a limb severed from a living person, which contains a whole bone with flesh around it in an amount that would have allowed it to survive and heal had it remained attached, and with the flesh connected by sinews - such a limb is a source of tumah, and it conveys tumah not only through touching and carrying but even through a tent, that is, by the mere fact of being under one roof with it, just like a corpse. The question under discussion is how far this limb resembles an actual corpse.
Three opinions in the dispute:
The dispute concerns the law of flesh or bone that became separated from the severed limb - the amputated leg, for example. We will begin with the language of the mishnah, and afterward summarize the various positions.
"Kezayis basar happoresh me'ever min hachai" - had this been a corpse, an olive's volume of flesh that separates from it conveys tumah. What is the law when the limb was separated from a person who was alive at the time of the separation? "Rabbi Eliezer metamei" - it is like a corpse, and it is a source of tumah. "VeRabbi Yehoshua veRabbi Nechunya metaharin" - the two Sages, from among the same three mentioned in the previous mishnah, say that once the flesh has separated from the severed limb, it no longer conveys tumah at all.
"Etzem kis'orah happoresh me'ever min hachai" - a fragment of bone the size of a barley grain, which, had it separated from a corpse, would convey tumah through touching and carrying. "Rabbi Nechunya metamei" - this bone fragment is tamei, not through a tent, but through touching and carrying. "VeRabbi Eliezer veRabbi Yehoshua metaharin" - bone fragments that separated from a severed limb do not convey tumah at all.
A summary of the three positions:
Rabbi Eliezer: the flesh that separated from the limb is tamei, but not the bone.
Rabbi Nechunya: the bone that separated from the limb is tamei, but not the flesh.
Rabbi Yehoshua: a limb from a living person must remain a complete limb; once flesh or bone has been separated from it, they no longer have any special status, and both are tahor.
The Sages' challenge to Rabbi Eliezer:
"Amru lo leRabbi Eliezer: mah ra'isa letamei kezayis basar happoresh me'ever min hachai?" - why do you declare the flesh tamei to begin with? "Amar lahem: matzinu ever min hachai kemeshulam" - a limb from a living person is compared to a complete corpse, "umah hameis - kezayis basar happoresh mimenu tamei, af ever min hachai - kezayis basar happoresh mimenu yitma": just as an olive's volume of flesh that separates from a corpse is a source of tumah, so too an olive's volume of flesh that separates from a severed limb.
Rabbi Yehoshua and Rabbi Nechunya answered him that his position does not hold together: you yourself distinguish between bone and flesh, a distinction that does not exist regarding a corpse, where bone and flesh are equally tamei. The very fact that you declare the bone tahor shows that you do not equate the limb with an actual corpse, and if so, there is no basis for saying that the flesh conveys tumah.
In the language of the mishnah: "Im timeisa kezayis basar happoresh min hameis - sheken timeisa etzem kis'orah happoresh mimenu" - with a corpse both are indeed tamei, and the reasoning works out well. "Tetamei kezayis basar happoresh me'ever min hachai - sheken tiharta etzem kis'orah happoresh mimenu?" - how can you declare tamei the flesh that separates from the severed limb, when in your own view the bone fragment that separates from it is tahor? Rabbi Eliezer offers no answer to this.
The same question to Rabbi Nechunya:
"Amru lo l'Rabbi Nechunya: mah ra'isa l'tamei etzem k'se'orah haporesh me'ever min hachai?" - Why, in your view, is a fragment of bone that separated from a severed limb tamei? "Amar lahem: matzinu ever min hachai k'meshulam" - a severed limb has the status of a complete corpse, "u'mah hameis - etzem k'se'orah haporesh mimenu tamei, af ever min hachai - etzem k'se'orah haporesh mimenu tamei": just as a fragment of bone from a corpse, even the size of a barley grain, is tamei, so too is a fragment of bone that comes from a limb severed from a living person.
Here too they answered him: if you equate the severed limb to a corpse, there is no room at all to distinguish between bones and flesh, yet you rule the bone tamei and the flesh tahor. In the words of the Mishnah: "Im timeisa etzem k'se'orah haporesh min hameis - shekein timeisa k'zayis basar haporesh mimenu" - with a corpse the two are of equal status. "T'tamei etzem k'se'orah haporesh me'ever min hachai - shekein tiharta k'zayis basar haporesh mimenu?" - and Rabbi Nechunya too has no answer.
Why does Rabbi Eliezer distinguish between flesh and bone?
"Amru lo l'Rabbi Eliezer: mah ra'isa lachlok midosecha? O tamei bishteihen o taher bishteihen!" - Why did you see fit to split the application of the laws between bone and flesh that come from a severed limb? Either make both tamei or make both tahor. Rabbi Eliezer answers with two reasons why flesh is more stringent than bone:
"Merubah tumas habasar mitumas ha'atzamos, shehabasar noheg bin'veilos u'vishratzim, mah she'ein kein ba'atzamos" - the carcass of a neveilah, a horse or a cow or a pig or a sheep, conveys tumah, but only its flesh and not its bones. So too with sheratzim, those small creeping creatures, a dead mouse or a mole and the like: the flesh conveys tumah while the bones do not. It emerges that flesh is a stronger source of tumah than bone.
"Davar acher: ever sheyeish alav basar kara'ui - metamei b'maga u'v'masa u'v'ohel" - as long as the limb has a proper amount of flesh on it, even if it is not one hundred percent, the limb conveys tumah not only through contact and through carrying, meaning direct touch and bearing its weight, but even through ohel. "Chasar habasar - tamei": if a little flesh is missing, as long as it could have healed over had the limb remained attached, it is still considered a limb and is tamei. "Chasar ha'etzem - tahor": if even the slightest bit of the bone is missing, so that it does not contain a whole bone, it is no longer a limb and it is tahor. It emerges that the bone must be one hundred percent complete, whereas with flesh ninety percent suffices - so flesh is the stronger source of tumah.
Why does Rabbi Nechunya distinguish between bone and flesh?
"Amru lo l'Rabbi Nechunya: mah ra'isa lachlok midosecha? O tamei bishteihen o taher bishteihen!" - and Rabbi Nechunya answers with three reasons why bone is more stringent than flesh:
"Merubah tumas ha'atzamos mitumas habasar, shehabasar haporesh min hachai tahor, v'ever haporesh mimenu v'hu bivri'aso tamei" - what makes the limb a source of tumah is the bone inside it. Flesh cut from a living person, even a large piece, even the entire tongue or the kidneys, is tahor; whereas a tiny limb, like a baby's little finger, as long as it is whole as it was created and has a bone inside it, is tamei and a source of tumah. Clearly, then, the bone is the essential element and not the flesh.
The shiurim of tumah: with flesh, a k'zayis conveys tumah in every way - through contact, through carrying and through ohel; whereas less than the shiur, even ninety-nine percent of it, is completely tahor. With bones, one of the shiurim is the majority of the bones, one hundred and twenty-five bones of the skeleton, which likewise convey tumah in every way; but if the shiur is lacking and one hundred and twenty-four bones remain, although they no longer convey tumah through ohel, they still convey tumah through contact and through carrying, since even a bone the size of a barley grain conveys tumah through contact and through carrying. It emerges that bones hold on to their tumah longer, which means they are a stronger source of tumah than flesh.
"Davar acher: kol b'sar hameis shehu pachos mik'zayis - tahor" - even a complete body, if it is tiny and its flesh does not amount to a k'zayis, is tahor. Whereas "rov binyano v'rov minyano shel meis" convey tumah regardless of any shiur: rov binyano is the majority of a person's frame, such as the thighs and the spine, even if a thigh bone or another bone is missing; and rov minyano is one hundred and twenty-five bones, even if they do not have the volume required for bone fragments gathered together, which is a rova hakav, about five hundred cubic centimeters. So, for example, with a tiny stillborn that was miscarried: even though all its flesh does not amount to a k'zayis, if it has the majority of a skeleton, its tiny bones convey tumah regardless of any shiur. Clearly, then, bones have a unique power that flesh does not have.
Rabbi Yehoshua's view:
Rabbi Yehoshua holds that neither bones nor flesh that separated from a severed limb convey tumah. There is a law called ever min hachai, a limb from a living person, and it is a source of tumah, but only when it is a complete limb. Once it has lost its status as a limb, because it lacks the required amount of bone or flesh, nothing is left of it, and it is not compared to a corpse at all, but is a separate law unto itself.
"Amru lo l'Rabbi Yehoshua: mah ra'isa l'taher bishteihen?" - Why did you see fit to rule tahor both the bone and the flesh that separated from a severed limb? "Amar lahem: lo, im amartem b'meis - shekein rov u'vinyan v'rakav, tomru b'chai she'ein bo rov u'vinyan v'rakav".
A corpse has unique categories of tumah: rov (the majority of the body), binyan (its skeletal structure), and rekev (decay). Rekev is the residue left by decomposition: a person who was laid without any clothing on a marble slab and remained there for many years - whatever remains of him transmits tumah even by way of a tent (ohel). With a limb severed from a living person, by contrast, there is no such thing as the majority of the limb, or the majority of its bones, or its rekev, serving as a source of tumah. Clearly, then, a corpse carries unique laws that do not apply at all to a severed limb.
Rabbi Yehoshua therefore says: a complete limb - the entire bone, the sinews that connect it, and all of its flesh, apart from a small amount that would have healed had the limb remained attached - is a category unto itself, called eiver min hachai (a limb from a living person). But anything less than that, whether it is missing bone or missing flesh, and likewise flesh or bone that separated from the limb, is completely tahor.
The halachah follows Rabbi Yehoshua, the third opinion: a complete limb from a living person is tamei, but anything less than that, as well as anything that separated from the limb, is completely tahor.