Explanation: They did not say exactly the same thing;

Shimon ha'Tzadik holds that only a Nazir Tamei is called a sinner. It is not because he pained himself, rather, because he regrets [his Nezirus];

R. Shimon and R. Elazar ha'Kapar hold that even a Nazir Tahor is called a sinner.

However, all agree that there is sin in Nezirus.

Explanation: This is why they enacted Konam, so he will say just Konam. If he would say Korban, he would say [also] "la'Shem", like the verse says.

Implied question: Regarding Cherem, in Yehudah it does not suffice to say just "Cherem", for Stam Cherem in Yehudah is [for Kohanim, and] not for Bedek ha'Bayis! (In any case he must say la'Shem!)

Answer: If he says Cherem, he will say [also] "la'Shem", like the verse says;

However, when he says Cherech, since it is not from a verse, he will not say "la'Shem", rather, "l'Bedek ha'Bayis."

Explanation: R. Shimon ben Gamliel comes to explain our Mishnah. When it says Nadar b'Mohi, he did not say just Mohi;

Rather, he said "the Mumsa that Mohi said", i.e. the Shevu'ah that Moshe swore, like it says "va'Yo'el Moshe Lasheves Es ha'Ish."

This is why the Mishnah says Nadar b'Mohi. Had he said Shevu'ah or Shekukah b'Mohi, this would imply that he said only b'Mohi;

Therefore, it taught Nadar, to teach that we require that he mention the Neder of Moshe, i.e. his Shevu'ah.

This is what R. Shimon ben Gamliel says, the Mumsa that Mohi said.

Alternate text: Some texts say [if he said] "b'Mumi [or] b'Mumsa", his words have no effect. "Mumi [and] Mumsa' are Kinuyim for Shevu'ah.

Explanation: R. Shimon ben Gamliel comes to teach that if he said with a "Beis", this is not a Kinuy for Shevu'ah;

When the Mishnah said b'Mohi, this does not mean that he said it with a Beis. Rather, he said it without a Beis.

Implied question: According to this text, why didn't the Mishnah teach "Shevusah Shekukah Mumi, and rather taught Nadar b'Mumi?

Answer: It is because Shevusah Shekukah are derived from Shevu'ah, unlike Mumi. Since they are different [classes of] Kinuyim, the Mishnah interrupted between them with "Nadar".

Explanation: In all of these, there is a Patach under the Lamed. Therefore, he is forbidden, for it connotes "Lo (not) Chulin", rather, Korban. "Lo Kasher", rather, Asur. Lo Dachi (Tahor)", rather, Asur.

We find Dachi regarding Heter, like we say (Eduyos 8:4) Yosi ben Yo'ezer testified that Ayil Kamtza (a species of grasshopper) is Dachen (Tahor, i.e. permitted to eat);

Also a verse writes "Kol Tzipor Tehorah", i.e. permitted. (It does not teach that it is not Tamei. Just the contrary, one who eats a Neveilah of a permitted species of birds becomes Tamei, but the forbidden species of birds have no Tum'ah at all!)

Therefore, when he said "Lo Kasher" or "Lo Dachi", he means, rather it is Asur.

Question: Perhaps he forbids due to Isur, and not due to Neder. This is like Matfis b'Devar ha'Asur (he makes something forbidden like a matter forbidden not due to Hekdesh or a Neder), which does not become forbidden!