One who vows that dates are forbidden to him is permitted to eat date honey. One who vows that late grapes are forbidden to him is permitted to eat vinegar of late grapes.
Rabbi Yehuda ben Beteira says: In the case of any food that the name of its derivative is called after its name, and one vows that the item is forbidden, he is also prohibited from consuming the liquid that emerges from it. But the rabbis permit this.
Here, the mishnah sets up parameters for when a derivative is permitted, and when it is forbidden. Although Rabbi Yehuda ben Beteira disagrees, the rabbis rule that in general, the liquid that comes out of a food — e.g., date honey or grape vinegar — is permitted. How does the Gemara understand their difference of opinion?
Rabbi Shimon ben Elazar said this principle: Anything that is commonly eaten, and it is also common to eat what emerges from it, for example, dates and date honey, if one vowed that it is forbidden to him, he is also prohibited from consuming what emerges from it.
Similarly, if one vows that what emerges from it is forbidden to him, he is also prohibited from partaking of it. And with regard to anything that is not commonly eaten as it is, and it is common to eat what emerges from it, if one vowed that he will not eat from it, he is prohibited from consuming only what emerges from it.
As we have seen before (Nedarim 49), the Gemara explains that the difference in ruling comes down to local custom. A person can consume derivatives of items that they vowed not to eat (e.g., no to dates, but yes to date honey) in places where the rawer form is not usually consumed.
The next mishnah deals with something a little different: Similar derivatives that are made from different items.
One who vows that wine is forbidden to him is permitted to partake of apple wine (i.e., cider). One who vows that oil is forbidden to him is permitted to partake of sesame oil. One who vows that honey is forbidden to him is permitted to eat date honey.
Does the Gemara agree? It depends.
It is taught in a beraita: With regard to one who vows that oil is forbidden to him, if he is in the land of Israel he is permitted to eat sesame oil and is prohibited from eating olive oil. And if he is in Babylonia, sesame oil is forbidden to him, and it is permitted for him to eat olive oil. If he takes the vow in a locale where people use both types of oil he is prohibited from eating both.
Similar to the ruling we encountered about local language on Nedarim 49, the Gemara rules that local custom will dictate the parameters of the vow. If she vowed not to consume “oil,” and oil is understood to mean olive oil when not used with a modifier, then sesame oil (my favorite) would be permitted, as it has a modifier and is uncommonly used. But, in a place where sesame oil is the more common variety and people use the word “oil” with no modifier to refer to it, then it would be prohibited, and olive oil permitted.
Several sources — biblical and halakhic — bear out these rulings. For example, those that abstain from wine during the nine days of semi-mourning prior to the commemoration of Tisha B’Av are permitted to drink beer and hard cider (the “apple wine” of our mishnah). While these beverages might be intoxicants, they are not prohibited because they are not, strictly speaking, wine. (Shaarei Teshuvah 551:10)
While this recital of case after case about such similar details might feel repetitive, I actually find the rabbis’ process fascinating. One of the things I find most interesting about this section of our tractate — and the Talmud as a whole — is the attempt of the rabbis to define rulings with both clarity and enough flexibility that they make practical sense to people living in different times and places — even, perhaps especially — to us, two millennia into the future.
Read all of Nedarim 53 on Sefaria.