Nedarim, Chapter Eleven, Mishnah Seven
Yesterday we learned that if when the husband/father annulled his wife/daughters vow he did not have full comprehension of who vowed, what type of vow they took, or what they prohibited, he must annul it again.
Generally the vow may be annulled only on the day that the husband/father hears of the vow (see 10:5). However, in this case he may annul the vow when he learns the details, even though the day that he heard the vow has passed, because for him the day that he learns of the vows correct details is considered the day that he heard the vow.
Our mishnah discusses a husband who did not know that he could annul the vow, or that there was even a vow to annul. The question is can he annul the vow when he learns that he has such a power, or that it was a vow.
1) [If the husband declares,] I knew that there were vows, but I did not know that they could be annulled, he may annul them [now].
2) [But if he says:] I knew that I could annul them, but I did not know that this was a vow,
a) Rabbi Meir says: he cannot annul it,
b) But the Sages say: he can annul.
Section one: In this case the husband/father knew that there was a vow, but did not know that he could annul the vow or that in general he can annul vows. The mishnah rules that he may annul the vow later when he learns that he has such a right. The day that he learns that he can annul vows is considered the day that he heard the vow.
Section two: In this case the father/husband knew that he has the right to annul vows in general, but did not know that what his daughter/wife had said was considered a vow. Hence he did not annul the vow on the day that he heard the original remark. When he later learns that this was a vow, Rabbi Meir says he can no longer annul it. Since he knew on the day that he heard the vow that he can annul vows, he should have annulled what she had said in any case, even though he was not sure that it was a vow. The Sages, however, rule that he may still annul the vow when he learns that it was truly a vow. According to their opinion, this is the day that is actually called the day that he heard the vow.