Nedarim 75b

כְּגוֹן דְּאַתְפֵּיס אַחֲרִינָא בְּהָדֵין נִדְרָא. אִי אָמְרַתְּ חָלִין — הָוְיָא תְּפִיסוּתָא. אִי אָמְרַתְּ לָא חָלִין — לָא אִיכָּא מְשָׁשָׁא.

The Gemara answers: There is a difference in a case where another person associated his own vow with this vow. If someone else heard her vow and declared his vow to be like hers, the status of his vow depends on this question. If you say that such vows take effect, then the association of the other person’s vow takes effect. If you say that such vows do not take effect at all, then the vow of the other person has no substance, as the vow with which he associated it never existed.

מַאי? תָּא שְׁמַע, אָמַר רַבִּי אֱלִיעֶזֶר: אִם הֵפֵר נְדָרִים שֶׁבָּאוּ לִכְלַל אִיסּוּר, לֹא יָפֵר נְדָרִים שֶׁלֹּא בָּאוּ לִכְלַל אִיסּוּר? שְׁמַע מִינַּהּ לָא חָלִין!

What, then, is Rabbi Eliezer’s opinion? Come and hear the mishna: Rabbi Eliezer said: If one can nullify vows that have reached the status of a prohibition, shall he not nullify vows that have not reached the status of a prohibition? Learn from it that such vows do not take effect at all, as they are described as not having reached the status of a prohibition.

מִי קָתָנֵי ״שֶׁאֵינָן בָּאִין״? ״שֶׁלֹּא בָּאוּ״ קָתָנֵי, עֲדַיִין לֹא בָּאוּ.

The Gemara rejects this conclusion: Does the mishna teach using the words: That do not reach the status of a prohibition? It teaches: That have not reached the status of a prohibition, which could mean that they have not yet reached the status of a prohibition, but they may take effect, momentarily, when she actually takes the vow.

תָּא שְׁמַע, אָמַר לָהֶן רַבִּי אֱלִיעֶזֶר: וּמָה בִּמְקוֹם שֶׁאֵין מֵיפֵר נִדְרֵי עַצְמוֹ מִשֶּׁנָּדַר, מֵיפֵר נִדְרֵי עַצְמוֹ עַד שֶׁלֹּא יָדוּר. מְקוֹם שֶׁמֵּפֵר נִדְרֵי אִשְׁתּוֹ מִשֶּׁתִּדּוֹר, אֵינוֹ דִּין שֶׁיָּפֵר נִדְרֵי אִשְׁתּוֹ עַד שֶׁלֹּא תִּדּוֹר?

Come and hear a baraita from the Tosefta ( Nedarim 6:5): Rabbi Eliezer said to them: And just as in a situation where he cannot nullify his own vows once he has vowed, he can nullify his own vows before he vows by stipulating beforehand that the vows he takes should not take effect, all the more so in a situation where he can nullify his wife’s vows even after she vows, is it not logical that he should be able to nullify his wife’s vows before she vows?

מַאי לָאו, דְּאִשְׁתּוֹ דּוּמְיָא דִּילֵיהּ, מָה [הוּא] דְּלָא חָיְילִין — אַף אִשְׁתּוֹ נָמֵי דְּלָא חָיְילִין? לָא, הָא כִּדְאִיתָא וְהָא כִּדְאִיתָא.

The Gemara explains the proof: What, is it not referring to where his wife’s vows are similar to his own in that just as his vows, which were nullified in advance, do not take effect at all, so too the vows of his wife do not take effect at all when nullified in advance? The Gemara rejects this: No, this case of his nullifying his own vows prior to taking them is as it is, and that case of his nullifying her vows prior to her taking them is as it is; the similarity between the two cases is sufficient for an a fortiori inference, but they are not similar in all respects.

תָּא שְׁמַע, אָמְרוּ לוֹ לְרַבִּי אֱלִיעֶזֶר: וּמָה מִקְוֶה שֶׁמַּעֲלֶה אֶת הַטְּמֵאִין מִטּוּמְאָתָן — אֵין מַצִּיל עַל הַטְּהוֹרִים מִלִּיטָּמֵא, אָדָם שֶׁאֵין מַעֲלֶה אֶת הַטְּמֵאִין מִטּוּמְאָתָן — אֵינוֹ דִּין הוּא שֶׁלֹּא יַצִּיל עַל הַטְּהוֹרִין מִלִּיטָּמֵא?

Come and hear a baraita : They said to Rabbi Eliezer: Your a fortiori inference is flawed, as can be seen from this example: And just as with regard to a ritual bath, which elevates the impure from their ritual impurity when they immerse in it but does not save the pure from becoming impure if they come into contact with impurity after immersion, so too, with regard to a person, who does not elevate the impure from their impurity, e.g., when a person swallows a ritually impure object and then immerses in a ritual bath, the object remains impure, is it not logical that he should not save pure items from becoming impure? When one who has swallowed a ritually pure object comes into contact with impurity, the object he has swallowed should also become impure. This is not the case, as a swallowed object does not become impure when the person who swallowed it does. Therefore the a fortiori argument is flawed, and one cannot derive from the ability to change a status, like the husband’s ability to nullify his wife’s vows or the ability of the ritual bath to render something ritually pure, that the source of the change can also prevent a change of status or preserve that status.

שְׁמַע מִינַּהּ לָא חָיְילִין!

However, learn from this baraita that, according to Rabbi Eliezer, vows nullified by the husband from the outset do not take effect at all, as the Rabbis’ objection presumes that according to Rabbi Eliezer, the vows do not take effect at all. Their argument is based on the analogy between preemptive nullification and preemptive prevention of impurity. Preemptive prevention of impurity is understood to be saving an item from ever becoming impure and analogously, preemptive nullification is understood to be preventing a vow from ever taking effect.