Question (Abaye): The Seifa of Mishnah #1 is unlike R. Eliezer!

(Seifa): Regarding a Safek Bechor, whether human or animal, whether it is a Kosher or Tamei species, the burden of proof (that it is a Bechor) is on the one who wants to take (the Kohen, who wants to get five Shekalim, the animal, or a Seh in place of a donkey).

(Beraisa): One may not shear (a Safek Bechor Beheimah) or work with it. (We are stringent, unlike R. Eliezer!)

Answer (R. Zeira): We are stringent about automatic Kedushah. We are lenient about Kedushah imposed by man (man does not intend to forbid doubtful cases).

Question (Beraisa - R. Meir and R. Eliezer): If a liquid became doubtfully Tamei, it has Tum'as Atzman (it itself is considered Tamei), but it is not Metam'ei other things.

Contradiction (Beraisa - R. Eliezer): Liquids cannot become Tamei at all (mid'Oraisa).

Support (R. Eliezer, for himself): Yosi ben Yoezer testified that Ayil Kamtza (a kind of locust) is Kosher, and that liquids (blood and water) of Beis Mitbechai (where they rinse Korbanos) are Tahor. (Tum'ah of liquids is only mid'Rabanan. Chachamim did not decree about them in the Mikdash.)

Answer: Shmuel explains 'they are Tahor', i.e. they are not Metam'ei other things, but they have Tum'as Atzman (mid'Oraisa). Therefore, we are stringent about Safek Tum'as Atzman.

Question: Rav holds that they lack even Tum'as Atzman (mid'Oraisa). How can he explain why R. Eliezer is stringent about a Safek?

Answer #2 (to contradiction 4a, 18b): Mishnah #1 is like R. Yehudah (he is lenient about Safek Nezirus), and our Mishnah is like R. Shimon (he is stringent):

(Beraisa #1 - R. Yehudah): If one said 'I am a Nazir if this pile is at least 100 Kor (a volume)', and the pile was stolen or lost, he is permitted (he is not a Nazir);

R. Shimon forbids.

Contradiction: Elsewhere, R. Yehudah holds that a person forbids himself through Safek!

(Mishnah - R. Yehudah): In Yehudah, if he said Terumah Stam, he is forbidden. In Galil, he is permitted, for there people are not familiar with Terumas ha'Lishkah.

Inference: If they were familiar with it, he would be forbidden (even though we are unsure what he intended)!

Answer #1 (Rava): In Beraisa #1, R. Yehudah holds that a person does not enter a Safek, for it is more stringent than Vadai (Nezirus).

A Vadai Nazir can shave (at the end of Nezirus) and bring Korbanos, and the Korbanos are eaten. A Safek Nazir cannot do so!

Question (Rav Huna bar Yehudah): If he said that he will be a Nazir Olam (for life), a Safek is not more stringent (in any case he can never shave)!

Answer (Rava): A Vadai Nazir Olam is more lenient. If his hair gets too long, he may cut it and bring three Korbanos. A Safek Nazir Olam may not do so.

Question (Rav Huna): If he said that he will be a Nazir (like) Shimshon (who may not cut his hair), a Safek is not more stringent!

Answer (Rava): No Beraisa says that R. Yehudah is lenient about Nezirus Shimshon. Our Beraisa discusses Stam Nezirus, not discuss Nezirus Shimshon.

Question (Rav Huna): R. Ada bar Ahavah said that a Beraisa explicitly says that R. Yehudah is lenient about Nezirus Shimshon!

Rava: I cannot answer this. (Alternatively - they argue about R. Yehudah's opinion.)

Answer #2 (Rav Ashi): In Beraisa #1, R. Yehudah cites R. Tarfon. He himself disagrees:

(Beraisa - R. Yehudah citing R. Tarfon): If David and Levi saw a man walking towards them, and David accepted Nezirus on condition that it is Ploni, and Levi accepted Nezirus on condition that it is not Ploni, neither of them is a Nazir, for Nezirus requires Hafla'ah (a definite acceptance).

Question: If so, why did the Beraisa say that the pile was stolen or lost? In any case he is not a Nazir!

Answer: The Beraisa discusses when it was stolen or lost to show the extremity of R. Shimon's opinion. Even in such a case, he holds that a person forbids himself due to Safek.

(Mishnah - R. Yehudah): In Yehudah, if he said Terumah Stam... (In Galil, he is permitted, for there people are not familiar with Terumas ha'Lishkah.)

Inference: If they were familiar with it, he would be forbidden. This shows that he is stringent about a Safek (what he intended).

Contradiction (Seifa): If he said Cherem Stam, in Yehudah he is permitted. In Galil he is forbidden, for people there are not familiar with Cherem of Kohanim.

Inference: If they were familiar with it, they would be permitted. This shows that he is lenient about a Safek!

Answer (Abaye): R. Elazar b'Ribi Tzadok taught the Seifa:

(Beraisa - R. Yehudah): In Yehudah, if one said Terumah Stam, he is forbidden;

R. Elazar b. R. Tzadok says, if one said Cherem Stam in Galil, he is forbidden.