Nazir chapter 7, mishnah 4. This mishnah deals with the remaining laws connected to the question of which forms of tumah require the nazir to shave and which do not, first among them the liability for entering the Temple.
The words of Rabbi Eliezer in the name of Rabbi Yehoshua:
"Kol tumah min hames shehanazir megaleiach alehah" - any tumah from a corpse for which the nazir shaves also carries liability for entering the Temple. One who enters the Temple while bearing such tumah is liable to bring a korban if he did so unwittingly, and is liable to kareis if he did so deliberately.
"Kol tumah min hames she'ein hanazir megaleiach alehah" - any tumah from a corpse for which the nazir does not shave carries no liability for entering the Temple.
It emerges that the distinction between the two categories of tumah is not relevant to the nazir's shaving alone, but also to the liability for entering the Beis HaMikdash in a state of tumah.
Rabbi Meir's objection:
Rabbi Meir disagrees and says: "Lo yehei zeh kal min hasheretz" - it stands to reason that the forms of corpse tumah for which the nazir does not shave should not be treated more leniently than a sheretz. One of the eight creeping creatures listed in the Torah, which convey tumah to a person when dead, does not carry the severity of corpse tumah in halachah, and nevertheless one who touches a dead sheretz, a mouse for example, is liable for entering the Beis HaMikdash. How, then, could these forms of tumah be treated more leniently than that? Rabbi Meir therefore holds that for every form of corpse tumah a person is liable for entering the Temple.
The point stands out all the more, since the tumah of a sheretz does not interrupt the nezirus at all and the nazir continues counting, whereas the other forms of corpse tumah, even though he does not shave for them and they do not turn the clock back, do prevent the time from counting toward his nezirus as long as the tumah is upon him. So even with regard to nezirus the sheretz is the more lenient case.
Rabbi Akiva's kal vachomer:
Rabbi Akiva relates: "Danti lifnei Rabbi Eliezer" - I presented the following kal vachomer before him:
A bone the size of a barley grain - a piece of bone the size of a barley grain does not convey tumah to a person in a tent, since tumah in a tent requires a quarter of a kav of bones. Even so, if a nazir touched it or moved it, he shaves for touching it and for carrying it.
A quarter-log of blood - a quarter-log of blood from a corpse does convey tumah to a person in a tent, and it is therefore more severe than a bone the size of a barley grain. "Eino din sheyehei hanazir megaleiach al maga'ah ve'al masa'ah?"
That is, if for a barley-grain of bone, the more lenient case, the nazir shaves for touching and carrying and turns the clock back, then all the more so for a quarter-log of blood, whose touching and carrying should not be treated as less than that of a barley-grain of bone.
And Rabbi Eliezer's response: "Mah zeh Akiva, ein danin kan kal vachomer" - one may not employ a kal vachomer in this case, and he did not explain his reasoning.
Rabbi Akiva continues: "Ucheshebati vehirtzeisi hadevarim lifnei Rabbi Yehoshua" - when I presented this argument before Rabbi Yehoshua, he said to me: "Yafeh amarta" - the kal vachomer is a sound argument, "ela kein amru halachah" - but this is a halachah handed down to us from Sinai: a barley-grain of bone conveys tumah and the nazir shaves for it, while for a quarter-log of blood he does not shave, even though according to the kal vachomer this does not seem to fit with logic. In any case, one cannot argue against a halachah from Sinai.
In summary: in this mishnah we learned that the distinction between the forms of tumah for which the nazir shaves and those for which he does not shave applies to the liability for entering the Temple as well, according to Rabbi Eliezer in the name of Rabbi Yehoshua. Rabbi Meir disagreed and argued that these forms of tumah cannot be more lenient than a sheretz, for which one who touches it is liable for entering the Temple. Finally we examined Rabbi Akiva's kal vachomer from a barley-grain of bone to a quarter-log of blood, and Rabbi Yehoshua's reply: although the argument is sound, the halachah from Sinai rules otherwise, and it is not subject to a kal vachomer.