We have already been introduced to Rabbi Yehuda’s teaching (see daf 55) that a person’s neder must be evaluated both by the words that are used as well as by external indicators of the person’s intentions. In our Mishna we find this idea presented by Rabbi Yehuda in the context of time. For example, if a person vows to drink no wine ad she-yehei ha-Pesah – “until it will be Passover” – we interpret it to mean that he will refrain from wine until the night of the seder. Given that a person is obligated to drink wine at the seder, we assume that he did not intend for his vow to extend to that night. Rabbi Yehuda’s son, Rabbi Yosei, adds another case. If a person vows to refrain from eating garlic ad she-tehei Shabbat – “until it will be Shabbat” – he is allowed to eat garlic on Friday night, since that is the common practice.
The novelty in Rabbi Yehuda’s position is that although the expression ad she-yehei is usually understood to mean until the end of the time that is mentioned, in these cases we will interpret the neder based on external evidence of his intentions, rather than on the usual meaning of the words. Both the Rambam and the Ramban suggest that Rabbi Yehuda disagrees with the position stated in the earlier Mishna, which would insist that a vow’s meaning be determined by common word usage. The Ramban explains that Rabbi Yosei goes one step further in suggesting that Rabbi Yehuda’s rule applies not only when the vow would affect a mitzva (like drinking wine at the seder) but even when it was just a minhag – an established tradition – like the case of eating garlic on Friday nights.
During Talmudic times (as well as afterwards) it was considered Jewish tradition to eat garlic. The Gemara (Bava Kamma 82a) offers a list of the many health benefits accrued by eating that vegetable. Cooked garlic was understood to increase sperm, which is why it was traditional to eat on Friday nights when marital relations are encouraged. In fact, eating garlic is listed as one of the ordinances established by Ezra HaSofer.