(Mishnah): Stam (unspecified) Nezirus is 30 days.

If one said 'I am a Nazir for one long [term]' or 'I am a Nazir for one short [term]', even if he said 'from here to the end of the world', he is a Nazir for 30 days.

If one said 'I am a Nazir and one day' or 'I am a Nazir and one hour' or 'I am a Nazir once and a half', he is a Nazir twice.

If one said 'I am a Nazir 30 days and an hour', he is a Nazir for 31 days, since a term of Nezirus is (a whole number of) days, and not hours.

(Gemara - Bar Kapara) Opinion #1: [We learn the duration of Stam Nezirus from the Gematriya of] Yihyeh - 30.

Opinion #2 (R. Shmuel bar Nachman citing R. Yehonason): It is [29,] corresponding to the 29 times in the Torah written in Parshas Nazir 'Neder', 'Nazir' [or other forms, e.g.] 'Lehazir.'

Question: There are 30 occurrences!

Answer (R. Yosi bei R. Bun): One is [needed] for its Chidush [to teach the laws of Nazir].

According to Bar Kapara, if one shaved on day 30, he was not Yotzei (30 full days are required). According to R. Yehonason, if one shaved on day 30, he was Yotzei (29 full days are required. It is better to say that the text here says 'R. Yehonason', like above, for he was the Rav Muvhak of R. Shmuel bar Nachman, rather than to change the text above to say 'Yochanan', like here. Also, below (11a) this opinion is attributed to R. Yonason. The Yerushalmi often omits the 'Hei' (and says Yudah or Yonason in place of Yehudah or Yehonason - PF)

Opinion #3: Some want to learn from "Gadel Pera Se'ar Rosho" - how much growth of hair is Pera? It is 30 days. (MAR'EH HA'PANIM - Aharon and his sons were told "Rosheichem Al Tifra'u" in their Aveilus, and for many matters, we find that Aveilus is 30 days.)

NOTE: The 30 days of Aveilus are mid'Rabanan! Perhaps we learn from the 30 days that Bnei Yisrael cried over Aharon (Bamidbar 20:29) and Moshe (Devarim 34:8). The Torah explicitly mentions seven days of Aveilus (Bereishis 50:10)! Perhaps we can join this to KORBAN HA'EDAH's Perush, that Gadel Pera is when one's hair feels heavy. It is hard to say that this is after seven days; it is reasonable to say so after 30 days.

Opinion #4: Some want to learn from "u'Vachsah Es Aviha v'Es Imah Yerach Yamim" - just like the days said there are 30, also the days said here ("Ad Melos ha'Yamim") are 30.

Opinion #5: Some want to learn from "veha'Yamim ha'Rishonim Yiplu Ki Tamei Nizro" - days that were additional, for Moshe and his Beis Din added them (i.e. the 30th day that is added to a month - NO'AM YERUSHALMI). It cannot be less than 30.

NOTE: He changes the text or reads it to say 'she'Hosiru' and 'she'Hosiran.' Every Beis Din of Kidush ha'Chodesh does so; perhaps the Gemara mentions Moshe, to teach that this Limud applied already from the time of Matan Torah. (PF)

Opinion #6: Some want to learn from "Ad Melos ha'Yamim." How much are full days? They are 30 days (i.e. a month that is made full).

Suggestion: If so (we learn from Melos, they must be full days, so), if one shaved on day 30, he was not Yotzei! (This is not a difficulty. Even though a Mishnah below says that he was Yotzei, above we said that Bar Kapara (a Tana) holds that he was not Yotzei. Indeed, some of the previous opinions must hold like him. We ask whether also this opinion must hold like him.)

Rejection (R. Yitzchak bar Elazar): "Yamim" is written Chaser, missing a Yud (to teach that a Chaser month of 29 days suffices. We explained this like MEICHAL HA'MAYIM.)