the gemara asks which of the 2 laws(a riviet of blood and the law of a barley sized bone)is a halacha moshe me'sinai(HMM) and which is learned from a kal vachomer.
my question: i understand how the law of a bone could be HMM and the law of blood is learn from it by a kal vechomer (as mentioned in the mishna: since the level of tumah of blood is greater than that of bone such that it is metameh by ohel, then certainly the stingency by bone(causes a nazir to shave) should apply to blood as well). however how is there a kal ve'chomer if the HMM is the blood, being that it appears that blood is the more chamur thing?
ike sultan, west orange, NJ
Tosfos explains that the Gemara's question is not which teaching is derived from a Kal v'Chomer, but rather which Halachah's starting point is a Halachah l'Moshe mi'Sinai. Everyone agrees that the teaching is deriving Revi'is Dam from Etzem k'Se'orah that it should also cause a Nazir to shave etc. The second possibility in our Gemara is that Revi'is Dam is a Halachah l'Moshe mi'Sinai that it is Metamei b'Ohel in general, after which we would derive from Etzem k'Se'orah via Kal v'Chomer that it should also cause a Nazir to shave etc. [When the Gemara says "Etzem k'Se'orah Kal v'Chomer," it means that we would derive that a Nazir shaves due to a Revi'is Dam b'Ohel using a Kal v'Chomer from Eztem k'Se'orah.]
All the best,
Yaakov Montrose