Today’s daf finds us in the midst of a series of mishnahs exploring the implications of vows forbidding consumption of various foods. The overarching question animating much of this material is whether a vow concerning a particular food also applies to byproducts of that food or to other similar foods. And as we’ve seen over and over in Nedarim, the answer depends to some extent on the specific wording of the vow.
Consider the mishnah that begins at the bottom of yesterday’s daf:
One who vows milk is forbidden, he is nonetheless permitted whey. But Rabbi Yosei prohibits it. If one vows that whey is forbidden, he is permitted milk.
Abba Shaul says: One who vows cheese is forbidden, it is prohibited whether salted or unsalted. One who vows meat is forbidden, gravy and sediments of boiled meat are both permitted. But Rabbi Yehuda prohibited them.
For the non-cheesemongers among you, whey is what is left over after an enzyme is added to warmed milk to curdle the proteins which are then strained off. It is, for all intents and purposes, refined milk. But for the rabbis, the change was sufficient that a vow concerning milk does not apply to whey and vice versa. Likewise for gravy and meat droppings. The majority opinion holds that these meat products are sufficiently removed from meat itself that a vow concerning the latter does not apply to the former.
This is in keeping with the larger thrust of the laws we’ve been studying on these pages. A mishnah later on today’s daf rules that one who vows not to consume grapes can still consume wine, while someone who vows not to consume olives can still consume its oil. As with milk and whey, fermenting wine from grapes or pressing oil from olives changes the substance sufficiently that the rabbis consider a vow about the former not to apply to the latter.
The exception is a case where one specifically vowed not to taste one of these forbidden foods. In this case, the vow isn’t about the food, but the taste of the food. So if one vows not to taste wine, then even a dish cooked in wine is forbidden. And if one vows not to taste olives or grapes, then oil and wine are also prohibited. This too is in keeping with broader principles we’ve been seeing throughout this tractate.
Back on Nedarim 47, we learned that if a father vows that his son cannot benefit from him, the son still inherits from the father after his death — except in a case where the father explicitly vowed that this shouldn’t happen either. The rabbis were highly attuned to the specific language of vows. A vow barring a son from benefiting from his father only applies to inheritance if the vow specified that it did. And a vow about grapes only applies to wine if the vow specifies that it’s the taste of grapes that is prohibited.
So if that’s the principle, what’s the deal with Rabbi Yosei prohibiting someone from eating whey when they only vowed about milk? The Gemara explains it like this:
In the rabbis’ locale they call milk, “milk” and whey, “whey.” In Rabbi Yosei’s locale, they also call whey, “milk whey.”
The difference is simply local custom. Where Rabbi Yosei lived, whey was called “milk whey,” so if someone there vowed about milk, it also applies to whey.
As we’ve seen many times already, the particular language of vows is of enormous significance. One word change can have real legal implications. But it’s also true that words don’t have objective and universal meaning across time and space. They mean different things in different places — which is as true in our day as it was in the time of the rabbis. If you make a vow, the precise words you use matters. But so does how those words are commonly understood in the place you live.
Read all of Nedarim 52 on Sefaria.