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מי שאמר הריני נזיר מגלח יום שלשים ואחד – for an unspecified Naziriteship is thirty days.

Introduction We have already had several opportunities to mention that a nazirite vow of unspecified duration is thirty days. Our mishnah deals with two related rulings.

ואם גלח יום שלשים יצא – for part of a day is considered an entire day.

If one says, “Behold, I am a nazirite,” he shaves on the thirty-first day. If he shaved on the thirtieth day, he has fulfilled his obligation. One who takes an nazirite vow of unspecified duration should shave on the thirty-first day, after he has observed thirty full days of naziriteship. However, if he shaves on the thirtieth day, he has still fulfilled his obligation to complete his naziriteship. This is because observing part of the day is counted as if he had observed the full day. Since he observed part of the thirtieth as a nazirite, it can count. You might note the similarity between this rule and the customs of shiva (the seven days in which one mourns close relatives). The seventh day of shiva is only observed in the morning because of this principle, that part of the day is as the full day. After “sitting shiva” in the morning of the seventh day, people customarily end shiva.

הריני נזיר שלשים יום אם גלח יום ל' לא יצא – for since he specified thirty complete days as stated.

[If, however, he says] “Behold, I am a nazirite for thirty days,” and shaves on the thirtieth day, he has not fulfilled his obligation. In this case he specifies that he will be a nazirite for thirty days. Since he said “thirty days” he must observe thirty full days. Should he shave on the thirtieth day he will not have fulfilled his obligation.