The Mishna on our daf teaches that a person who vows not to drink wine “today” only needs to refrain from drinking wine until nightfall. In the Gemara, Rav Yirmeya bar Abba rules that the Mishna’s ruling notwithstanding, in such a case the person must go to a rabbi to be sho’el on his neder (to request that the vow be annulled).
The Shitta Mekubetzet and others write that Rav Yirmeya is not explaining the Mishna, rather he is adding an additional injunction to the basic law; according to the Mishna, there would be no need to be sho’el on the neder at nightfall. The Rashba writes that even Rav Yirmeya would agree that in a case where a person vows to fast for the day, he can begin eating at nightfall, since it is clear that the person’s intention was to fast only until nightfall.
Two reasons are presented by the Gemara in explanation of Rav Yirmeya’s ruling:
- Rav Yosef says that it is a rabbinic injunction that is applied because we are afraid that a person may confuse a case of taking a vow “today” with a case where a person vows to refrain from drinking wine “for one day.” According to the Mishna, taking a vow not to drink wine “for one day” obligates the person to keep the neder for a 24 hour period.
- Ravina quotes Rav Yosef as saying that Rav Yirmeya is following the ruling of Rabbi Natan who believes that making nedarim and keeping them is equivalent to building a forbidden altar and sacrificing on it (see yesterday’s daf). Thus, even if the vow was fulfilled, we still recommend that it be annulled by a rabbi.
According to many of the rishonim (Tosafot, the Rosh, the Rashba, the Ran), Ravina is not disagreeing with Rav Yosef’s original explanation, rather he is adding a further reason for Rav Yirmeya’s ruling. The Rosh and Ran add that according to this explanation, if the neder that was made was a mitzva, there would be no need to annul it.