Our daf begins with a mishnah:
One who says: “This fruit is forbidden for me,” “it is forbidden upon my mouth,” or “it is forbidden to my mouth,” — it is forbidden to eat its replacements or what grows from it.
One who says, “These fruits are forbidden that I eat them” or “that I taste them,” — its replacements or what grows from it are permitted, for something that the seeds cease to exist (after it is sown). However, for something that the seeds do not cease to exist, even what grows from its growth is forbidden.
Depending on how the vow is stated, according to this mishnah, the derivatives of the fruit that the person has vowed to abstain from are also forbidden. Tosafot Yom Tov, otherwise known as Rabbi Yom-Tov Lipmann Heller, the 17th-century Polish talmudic commentator, points out that this mishnah seems to contradict another mishnah found in Tractate Terumot (9:4):
What grows from terumah (produce set aside for the priests, and therefore forbidden to the one who grew it) is terumah.
What grows from the growth of terumah is chullin (unsanctified produce which is permitted to the one who grew it) … the growth of hekdesh (dedicated for Temple use) and ma’aser sheni (set aside to be consumed in Jerusalem) is chullin and can be redeemed at the time it was planted.
In this second mishnah, we are talking about terumah, ma’aser sheni and hekdesh — different kinds of produce dedicated for Temple personnel, consumption within the city where the Temple stands or Temple use — and not produce that a person has vowed not to consume. But the consequences are similar: Both that which has been forbidden by vow and that which are set aside for priests, consumption in Jerusalem, or Temple use, are in fact, forbidden. The language of the vow even suggests that the nature of the prohibition is similar.
The inconsistency Tosafot Yom Tov points out is that the growth of the growth of terumah and the growth of hekdesh are all chullin — ordinary foods, not forbidden in any way. But in today’s mishnah, when someone makes a vow forbidding produce to him or herself, the growth — and in some cases even the growth of the growth — is forbidden. So why would the sages have thought derivatives were permitted in some cases but not others?
Tosafot Yom Tov and others answer that the difference is that when the growth is permitted, it is because these particular items are in a category called davar sheyesh lo matirin, something that is forbidden for now but is in some way permitted in the future. The concept is employed in other cases, for example: Hametz is forbidden on Passover, but once Passover has ended, the hametz is permitted.
The Jerusalem Talmud (Nedarim 6:4) discusses whether or not, like hekdesh (things consecrated for the Temple), for example, items one has vowed not to consume are included in the category of davar sheyesh lo matirin, items whose prohibition is not indefinite. They are included, the Jerusalem Talmud argues, because one can be released from one’s vow by asking a sage to annul it. In a few pages, on Nedarim 59, we will learn a similar view.
This view dramatically limits the power of a vow: One can make a vow (meant to be something permanent) knowing it is not necessarily permanent. At the same time, perhaps, this limitation makes vows more feasible for fallible humans. Humans make mistakes, encounter unforeseen situations and sometimes cannot fulfill what they wish they could. With the ability to annul a vow, one can make a vow knowing that, in the extreme case where one cannot fulfill it, one will not be stuck. It allows us to strive for something without being held back by a fear of being unable to attain it.
Read all of Nedarim 57 on Sefaria.