Halacha

הלכה א
מֵפֵר אָדָם אוֹ מְקַיֵּם דִּבְרֵי אִשְׁתּוֹ אוֹ בִּתּוֹ בִּכָל לָשׁוֹן וְאַף עַל פִּי שֶׁאֵינָהּ מַכֶּרֶת. שֶׁאֵין הָאִשָּׁה צְרִיכָה לִשְׁמֹעַ הַהֲפָרָה אוֹ הַקִּיּוּם:
כסף משנה
1.
A man may nullify or accept the [vows] of his wife or daughter in any language, even though she does not understand it, for the woman need not hear the nullification or the acceptance [of her vow].1See Chapter 12, Halachah 18, which explains that even if the woman intended to transgress, if her father or husband nullified the vow beforehand, she is not liable.

הלכה ב
וְכֵיצַד מֵפֵר. אוֹמֵר מוּפָר אוֹ בָּטֵל אוֹ אֵין נֵדֶר זֶה כְּלוּם וְכַיּוֹצֵא בִּדְבָרִים שֶׁעִנְיָנָם עֲקִירַת הַנֵּדֶר מֵעִקָּרוֹ. בֵּין בְּפָנֶיהָ בֵּין שֶׁלֹּא בְּפָנֶיהָ. אֲבָל אִם אָמַר לָהּ אִי אֶפְשִׁי שֶׁתִּדֹּרִי אוֹ אֵין כָּאן נֵדֶר הֲרֵי זֶה לֹא הֵפֵר. וְכֵן הָאוֹמֵר לְאִשְׁתּוֹ אוֹ לְבִתּוֹ מָחוּל לִיךְ אוֹ מֻתָּר לִיךְ אוֹ שָׁרוּי לִיךְ וְכָל כַּיּוֹצֵא בְּעִנְיָן זֶה לֹא אָמַר כְּלוּם. שֶׁאֵין הָאָב וְהַבַּעַל מַתִּיר כְּמוֹ הֶחָכָם אֶלָּא עוֹקֵר הַנֵּדֶר מִתְּחִלָּתוֹ וּמְפֵרוֹ:
כסף משנה
2.
How does he nullify [the vow]? He says: "It is nullified," "It is void," "This vow is of no consequence,"2Although the Shulchan Aruch (Yoreh De'ah 234:37) mentions the Rambam's view, it also mentions that of Rabbenu Asher who maintains that this last phrase is not effective in nullifying a vow. or uses other terms that imply that the vow is nullified from the outset, whether in the woman's presence or in her absence.
If, however, he tells her: "I cannot bear your taking a vow" or "This is not a vow," he did not nullify it.3For his wording does not imply that the vow is nullified. Similarly, if he tells his wife or his daughter: "[Your vow] is forgiven," "[It] is released," "[It] is absolved," or the like, his statements are of no consequence.4I.e., although these expressions are effective for a sage when absolving a vow, they are not effective for a husband or a father. For a father and a husband do not release a vow like a sage does, but instead, uproot the vow from the outset and nullify it.5In his Commentary to the Mishnah (Nedarim 13:8), the Rambam explains the statements he makes here. The term "nullify" implies nullifying an entity to the extent that it is as if it never existed. "Releasing," by contrast, implies that a connection existed, but it was released and will not have any effect in the future.
The Rambam's statements have aroused the attention of the commentaries for they appear to run contrary to the understandings of other authorities and the Rambam's own rulings. To explain: From Halachah 15 of this chapter and from Chapter 12, Halachah 19, it appears that until a father or a husband nullifies a vow, the vow is binding. Even when he nullifies it, the nullification affects only the future. See Hilchot Nazirut 9:11. When a sage absolves a vow, by contrast, it is as if the vow was never taken. See Hilchot Ishut 7:8-9, Hilchot Nazirut 3:10.
The Kessef Mishneh explains that the terminology employed by the Rambam here can be explained as follows: A sage does not "uproot" a vow, he causes it to be considered as if a vow not taken originally. A father or a husband, by contrast, uproot a vow, causing an entity that did exist to be nullified.

הלכה ג
וְכֵיצַד מְקַיֵּם. כְּגוֹן שֶׁיֹּאמַר לָהּ קַיָּם לֵיכִי אוֹ יָפֶה נָדַרְתְּ אוֹ אֵין כְּמוֹתֵךְ אוֹ אִלּוּ לֹא נָדַרְתְּ הָיִיתִי מַדִּירֵךְ וְכָל כַּיּוֹצֵא בִּדְבָרִים שֶׁמַּשְׁמָעָן שֶׁרָצָה בְּנֵדֶר זֶה:
כסף משנה
3.
How does one express his acceptance of a vow? He says to her: "I uphold your vow," "It was good that you vowed," "There is no one like you," "Had you not taken the vow, I would have administered it to you," or any analogous statement that implies that he is happy with this vow.

הלכה ד
הַמְבַטֵּל נִדְרֵי אִשְׁתּוֹ אוֹ בִּתּוֹ אֵינוֹ צָרִיךְ לוֹמַר כְּלוּם וְנִתְבַּטְּלוּ כָּל הַנְּדָרִים:
כסף משנה
4.
When a person voids the vows of his wife or daughter, it is not necessary for him to say anything6I.e., the Rambam is making a distinction between hafarah, "nullification," and bittul, voiding as he proceeds to explain. See also his Commentary to the Mishnah, loc. cit.,, where he elaborates on the distinction between these two activities. and all of the vows are nullified.

הלכה ה
וּמַהוּ הַבִּטּוּל שֶׁיָּכֹף אוֹתָהּ לַעֲשׂוֹת דָּבָר שֶׁאָסְרָה אוֹתוֹ. אֲבָל הַהֲפָרָה אֵינוֹ כּוֹפֶה אוֹתָהּ אֶלָּא מֵפֵר לָהּ וּמְנִיחָהּ אִם רָצְתָה עוֹשָׂה וְאִם רָצְתָה אֵינָהּ עוֹשָׂה:
כסף משנה
5.
What is meant by voiding? That he forces her to do something that she forbade herself to do.7E.g., if she took a vow not to drink wine, he causes her to drink wine.
The Ra'avad differs with the Rambam, maintaining that there is no concept of voiding a woman's vow by causing her to break it. Such concepts apply only with regard to servants. The Radbaz explains the Rambam's wording, stating that with regard to servants, it is necessary to actually compel them to break their vows. Such conduct is not appropriate with regard to one's wife or daughter. Nevertheless, if a husband or a father gently cause a woman to break their vow, that vow is nullified. The Shulchan Aruch (Yoreh De'ah 234:39) mentions both views though it appears to favor the Ra'avad's view.
Nullification, by contrast, does not involve forcing her. Instead, he nullifies the vow verbally and allows her [to do as she desires]. If she desires, she may act [in violation of the vow]. If she desires, she need not.8I.e., since the vow has been nullified, she is under no obligation to keep it. On the other hand, she is not obligated to perform the act forbidden by the vow..

הלכה ו
כֵּיצַד. נָדְרָה אוֹ נִשְׁבְּעָה שֶׁלֹּא תֹּאכַל אוֹ שֶׁלֹּא תִּשְׁתֶּה וְאָמַר לָהּ מוּפָר לָךְ הֲרֵי זֶה הֵפֵר וּמֻתֶּרֶת לֶאֱכל וְלִשְׁתּוֹת. נָטַל וְנָתַן לָהּ וְאָמַר לָהּ טְלִי וְאִכְלִי טְלִי וּשְׁתִי הֲרֵי זוֹ אוֹכֶלֶת וְשׁוֹתָת וְהַנֵּדֶר בָּטֵל מֵאֵלָיו:
כסף משנה
6.
What is implied? She took a vow or an oath not to eat or not to drink and he told her: "It is nullified for you." It is nullified and she is permitted to eat and to drink. If he took it and gave it to her, saying: "Take this and eat it," "Take this and drink," she may eat and drink and the vow is automatically nullified.9Without him saying anything.

הלכה ז
הַמֵּפֵר נִדְרֵי בִּתּוֹ אוֹ אִשְׁתּוֹ צָרִיךְ לְהוֹצִיא בִּשְׂפָתָיו. וְאִם הֵפֵר בְּלִבּוֹ אֵינוֹ מוּפָר. אֲבָל הַמְבַטֵּל אֵינוֹ צָרִיךְ לְהוֹצִיא בִּשְׂפָתָיו אֶלָּא מְבַטֵּל בְּלִבּוֹ בִּלְבַד וְכוֹפֶה אוֹתָהּ לַעֲשׂוֹת בֵּין עָשְׂתָה בֵּין לֹא עָשְׂתָה בָּטֵל הַנֵּדֶר:
כסף משנה
7.
When a person nullifies the vows of his wife or daughter, he must make a verbal statement of nullification. If he nullifies it within his heart, [the vow] is not nullified. When, however, he voids [their vows], he does not have to make a verbal statement. Instead, he nullifies the vow in his heart and compels her to perform [the deed]. Whether she performs it or not, the vow is nullified.

הלכה ח
מְפֵרִין נְדָרִים בְּשַׁבָּת בֵּין לְצֹרֶךְ הַשַּׁבָּת בֵּין שֶׁלֹּא לְצֹרֶךְ הַשַּׁבָּת. וְלֹא יֹאמַר לָהּ בְּשַׁבָּת מוּפָר לִיךְ כְּדֶרֶךְ שֶׁאוֹמֵר בְּחל אֶלָּא מְבַטֵּל בְּלִבּוֹ וְאוֹמֵר לָהּ טְלִי אִכְלִי טְלִי וּשְׁתִי וְכַיּוֹצֵא בָּזֶה:
כסף משנה
8.
We may nullify vows on the Sabbath, whether for the sake of the Sabbath10I.e., she took a vow not to wear jewelry or not to partake of a particular food. or not.11Even though the vow has no connection to the Sabbath and it is forbidden to perform any activity for the weekdays on the Sabbath, we allow him to nullify it. The rationale is that, otherwise, he will not be able to nullify it on Saturday night, because the time for nullification will have already passed. As stated in Hilchot Sh'vuot 6:6, on the Sabbath, a sage may absolve only those vows that concern the Sabbath (Kessef Mishneh). On the Sabbath, however, one should not, however, tell [his wife or daughter]: "[Your vow] is nullified," as one would say during the week.12Because it is the Sabbath, it is preferable to change the wording one uses. Even if one uses this wording during the week, the vow is nullified, as indicated by Halachah 6. Instead, he should nullify [the vow] in his heart and tell her: "Take this and eat it," "Take this and drink," or the like.

הלכה ט
הָאוֹמֵר לְאִשְׁתּוֹ אוֹ לְבִתּוֹ כָּל הַנְּדָרִים שֶׁתִּדֹּרִי מִכָּאן וְעַד שֶׁאָבוֹא מִמָּקוֹם פְּלוֹנִי הֲרֵי הֵן קַיָּמִין אוֹ הֲרֵי הֵן מוּפָרִין לֹא אָמַר כְּלוּם. עָשָׂה שָׁלִיחַ לְהָפֵר לָהּ אוֹ לְקַיֵּם לָהּ אֵינוֹ כְּלוּם שֶׁנֶּאֱמַר (במדבר ל יד) "אִישָׁהּ יְקִימֶנּוּ וְאִישָׁהּ יְפֵרֶנּוּ". וְכֵן הָאָב בְּעַצְמוֹ וְלֹא בִּשְׁלוּחוֹ:
כסף משנה
9.
When a person tells his wife or his daughter: "All the vows that you will take from now until I come from this and this place are upheld" or "...are nullified," his words are of no substance.13This concept is also derived from the prooftext cited below. Until a vow comes into existence and can be upheld, it cannot be nullified (Turei Zahav 234:28).
If he appointed an agent to nullify her vows or to uphold them, his act is of no substance, as [implied by Numbers 30:14]: "Her husband will uphold them, her husband will nullify them." Similarly, her father must act on his own, not through an agent.

הלכה י
אָסְרָה עַצְמָהּ בִּתְאֵנִים וַעֲנָבִים בֵּין בְּנֵדֶר בֵּין בִּשְׁבוּעָה. בֵּין שֶׁאָסְרָה עַצְמָהּ בְּכָל הַמִּין. בֵּין שֶׁאָמְרָה תְּאֵנִים וַעֲנָבִים אֵלּוּ. וְקִיֵּם לִתְאֵנִים וְהֵפֵר לַעֲנָבִים. אוֹ שֶׁקִּיֵּם לַעֲנָבִים וְהֵפֵר לִתְאֵנִים. מַה שֶּׁקִּיֵּם קַיָּם וּמַה שֶּׁהֵפֵר מוּפָר. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה. וְאֵין אוֹמְרִין בַּהֲפָרָה נֵדֶר שֶׁהוּפַר מִקְצָתוֹ הוּפַר כֻּלּוֹ כְּדֶרֶךְ שֶׁאוֹמְרִין בְּהַתָּרָה:
כסף משנה
10.
[When a woman takes a vow,] forbidding herself to [partake of] figs and grapes, whether through a vow or through an oath, whether she forbade herself from [partaking of] all types of the species or she said: "These figs and these grapes," if [her husband] upheld [the vow] concerning figs and nullified that concerning grapes or upheld [the vow] concerning grapes and nullified that concerning figs, what he upheld is binding and what he nullified is nullified. Similar laws apply in all analogous situations. With regard to the nullification of a vow, we do not say that when a portion of a vow has been nullified, the entire vow is nullified, as is said with regard to the absolution of vows.14See Chapter 4, Halachah 11, Chapter 8, Halachah 6. The rationale is that a sage nullifies the vow from the outset, causing it to be considered as if it were never taken. Therefore the entire vow is considered as a single entity. A husband, by contrast, nullifies a vow as it exists. Hence, each element of the vow can be considered independently.
The Rambam's ruling is quoted by the Shulchan Aruch (Yoreh De'ah 234:36). The Tur and the Rama differ and maintain that a husband must also nullify the entire vow. Once a portion of a vow is upheld, the vow cannot be nullified.

הלכה יא
מִי שֶׁנָּדְרָה אִשְׁתּוֹ וְשָׁמַע וְהִתְפִּיס עַצְמוֹ בְּנִדְרָהּ אֵינוֹ יָכוֹל לְהָפֵר שֶׁהֲרֵי קִיֵּם לָהּ. נָדַר הוּא וְהִתְפִּיסָה עַצְמָהּ בְּנִדְרוֹ מֵפֵר אֶת שֶׁלָּהּ וְשֶׁלּוֹ קַיָּם:
כסף משנה
11.
When a man's wife takes a vow and he hears it and extends the vow to apply to him,15See Chapter 3, Halachah 3, for an explanation regarding the convention of extending a vow. he cannot nullify it. [The rationale is that] he [already] upheld it.16For by attaching himself to her vow, he shows that he considers it a viable entity. If he took a vow and she extended it and applied it to herself, he may nullify her vow, but his vow is binding.

הלכה יב
כֵּיצַד. שָׁמַע אִשְׁתּוֹ אוֹ בִּתּוֹ אוֹמְרִין הֲרֵינִי נְזִירָה וְאָמַר וַאֲנִי. אֵינוֹ יָכוֹל לְהָפֵר וּשְׁנֵיהֶם נְזִירִים. אָמַר הוּא הֲרֵינִי נָזִיר וְשָׁמְעָה הִיא וְאָמְרָה וַאֲנִי. מֵפֵר לָהּ וְשֶׁלּוֹ קַיָּם. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
12.
What is implied? He heard his wife or his daughter say: "I am a nazirite," and said: "And I am also," he cannot nullify [her vow]17As Nedarim 3a states, the laws that apply to the nullification of other vows also apply to the nullification of nazirite vows. and they are both nazirites.18For the reason mentioned in the previous halachah. If he said: "I am a nazirite," and she heard and said: "And so am I," he may nullify her vow and his vow is still binding.19For his vow is not at all dependent on hers. Similar laws apply in all analogous situations.

הלכה יג
נָדַר לְעַצְמוֹ וְהִדִּירָהּ כְּמוֹתוֹ וְגָמַר בְּלִבּוֹ לְהַדִּירָהּ וְאָמְרָה אָמֵן הֲרֵי זֶה אֵינוֹ יָכוֹל לְהָפֵר. וְאִם נָדַר וְהִדִּירָהּ דֶּרֶךְ שְׁאֵלָה לֵידַע מַה בְּלִבָּהּ כְּמוֹ שֶׁאָמַר לָהּ הֲתִרְצִי בְּנֵדֶר זֶה לִהְיוֹת כְּמוֹתִי אוֹ לֹא וְאָמְרָה אָמֵן הֲרֵי זֶה מֵפֵר לָהּ:
כסף משנה
13.
When a husband takes a vow and administers an identical vow to his wife, having made a certain decision to administer the vow to her, if she says Amen,20She must, however, state her consent, for he cannot compel her to take a vow against her will. See Chapter 2, Halachah 1. he may not nullify it. If he took a vow and administered it to her as a question to see what she felt about it, e.g., he asked her "Do you desire to be like me [by taking] this vow or not?" If she says: Amen, he may nullify her vow.

הלכה יד
כֵּיצַד. אָמַר לָהּ הֲרֵינִי נָזִיר וְאַתְּ כְּלוֹמַר וְאַתְּ נְזִירָה כְּמוֹתִי וְאָמְרָה אָמֵן אֵינוֹ יָכוֹל לְהָפֵר. אָמַר לָהּ הֲרֵינִי נָזִיר וּמַה תֹּאמְרִי הַאַתְּ נְזִירָה כְּמוֹתִי וְאָמְרָה אָמֵן הֲרֵי זֶה יָפֵר. וְאִם הֵפֵר לָהּ שֶׁלּוֹ בָּטֵל שֶׁזֶּה כְּמִי שֶׁתָּלָה נִדְרוֹ בְּנִדְרָהּ. אָמְרָה לוֹ הֲרֵינִי נְזִירָה וְאַתָּה וְאָמַר אָמֵן אֵינוֹ יָכוֹל לְהָפֵר. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
14.
What is implied? He said: "I am a nazirite and so are you," i.e., you are a nazirite just like me. If she says Amen, he may not nullify her vow.21He is forbidden to nullify his wife's vow, because by doing so, his own vow would be nullified as stated in the conclusion of the halachah. Since he is forbidden to cause his own vow to be nullified, he is forbidden to nullify her vow (see Nazir 22b).
If he says: "I am a nazirite. What do you say? Will you be a nazirite like me?" If she says Amen, he may nullify her vow.22For his commitment is not dependent on hers at all. Even if she refuses to accept a nazirite vow, he is obligated to keep his vow. Hence, his right to nullify her vow is intact. If he nullifies her vow, his vow is also nullified. It is as if he made his vow dependent on her vow.23This refers to the first clause. It is as if he made his vow and her vow a single statement. Thus nullifying her vow would cause his vow also to be nullified. This is forbidden, because he is bound to uphold his vow. Nevertheless, after the fact, if he does nullify her vow, his vow is also nullified (Radbaz). See the Nekudot HaKessef [to Shulchan Aruch (Yoreh De'ah 234:54)] who explains that the Rambam's version of Nazir 22b follows the Jerusalem Talmud and differs from the standard text of the Babylonian Talmud.
If she told him: "I am a nazirite. What about you?", if he answered Amen, he cannot nullify [her vow].24As stated in Halachah 11. Similar laws apply in all analogous situations.

הלכה טו
הָאִשָּׁה שֶׁנָּדְרָה וְשָׁמַע אַחֵר וְהִתְפִּיס עַצְמוֹ בְּנִדְרָהּ וְאָמַר וַאֲנִי. וְשָׁמַע אָבִיהָ אוֹ בַּעְלָהּ וְהֵפֵר לָהּ שֶׁלָּהּ מוּפָר וְזֶה שֶׁהִתְפִּיס עַצְמוֹ חַיָּב:
כסף משנה
15.
[The following rules apply when] a woman takes a vow and another person extends the scope of the vow to include himself, saying "And I [as well]." If her father or husband hears of the vow and nullifies it, her vow is nullified, but that of the person who extended the vow is not.25The rationale for this ruling is that the husband's nullification affects the vow only from the time he made it onward. It does not nullify it from the outset. Hence, any extension of a vow that was made before the vow is nullified is binding [Radbaz; Shulchan Aruch (Yoreh De'ah 234:51)].

הלכה טז
הָאִשָּׁה שֶׁאֵין לָהּ בַּעַל וְאֵינָהּ בִּרְשׁוּת אָב וְאָמְרָה הֲרֵי הַבָּשָׂר אָסוּר עָלַי לְאַחַר שְׁלֹשִׁים יוֹם וְנִשֵּׂאת בְּתוֹךְ שְׁלֹשִׁים יוֹם. אַף עַל פִּי שֶׁבְּשָׁעָה שֶׁחָל הַנֵּדֶר הֲרֵי הִיא בִּרְשׁוּת הַבַּעַל אֵינוֹ יָכוֹל לְהָפֵר. שֶׁבִּשְׁעַת הַנֵּדֶר לֹא הָיְתָה בִּרְשׁוּתוֹ וְעַל זֶה נֶאֱמַר (במדבר ל י) "וְנֵדֶר אַלְמָנָה וּגְרוּשָׁה" וְגוֹ'. וַאֲפִלּוּ הָיְתָה מְאֹרֶסֶת לוֹ בִּשְׁעַת הַנֵּדֶר. שֶׁאֵין הַבַּעַל מֵפֵר בְּקוֹדְמִין כְּמוֹ שֶׁבֵּאַרְנוּ:
כסף משנה
16.
[The following rules apply concerning] a woman who is unmarried and not in her father's domain who says: "Meat will be forbidden to me after 30 days" and she marries within those 30 days. Even though she is in her husband's domain at the time the vow takes effect, he cannot nullify it. [The rationale is that] at the time the vow was taken she was not in his domain. Concerning such a situation, it was said [Numbers 30:10]: "The vow of a widow or a divorcee... shall remain standing." [This applies] even if she was consecrated to [her husband] at the time she took the vow, for a husband may not nullify26I.e., alone, without the nullification of the father (Chapter 11, Halachah 10). [vows that were taken] before [the marriage is consummated], as we explained.27Chapter 11, Halachot 20, 22.

הלכה יז
נָדְרָה תַּחַת בַּעְלָהּ שֶׁיִּהְיֶה הַבָּשָׂר אָסוּר עָלֶיהָ לְאַחַר שְׁלֹשִׁים יוֹם. אוֹ שֶׁתִּהְיֶה נְזִירָה לְאַחַר שְׁלֹשִׁים יוֹם. וְהֵפֵר לָהּ בַּעְלָהּ וּמֵת אוֹ גֵּרְשָׁהּ בְּתוֹךְ שְׁלֹשִׁים יוֹם. אַף עַל פִּי שֶׁבְּשָׁעָה שֶׁהָיָה לַנֵּדֶר לָחוּל הֲרֵי הִיא גְּרוּשָׁה אוֹ אַלְמָנָה הֲרֵי זוֹ מֻתֶּרֶת שֶׁכְּבָר הֵפֵר לָהּ נֵדֶר זֶה:
כסף משנה
17.
[The following rules apply if a woman] took a vow while under her husband's domain that meat will become forbidden to her after 30 days or that she will become a nazirite after 30 days and her husband nullified her vow, but he died or divorced her within those 30 days. Although she will be a divorcee or a widow when the vow will take effect, she is not bound by it, because [her husband] already nullified this vow for her.28I.e., whether or not his nullification takes effect depends on their relationship at the time he nullifies the vow (Nedarim 89a).

הלכה יח
אַלְמָנָה אוֹ גְּרוּשָׁה שֶׁאָמְרָה הֲרֵינִי אֲסוּרָה בְּיַיִן כְּשֶׁאֶנָּשֵׂא וְנִשֵּׂאת אֵין הַבַּעַל יָכוֹל לְהָפֵר. אָמְרָה וְהִיא תַּחַת בַּעְלָהּ הֲרֵינִי אֲסוּרָה בְּבָשָׂר כְּשֶׁאֶתְגָּרֵשׁ הֲרֵי הַבַּעַל מֵפֵר וּכְשֶׁתִּתְגָּרֵשׁ תִּהְיֶה מֻתֶּרֶת:
כסף משנה
18.
When a widow or a divorcee says: "Wine will be forbidden to me when I marry," [if] she marries, her husband cannot nullify the vow.29Because he cannot nullify the vows that were taken before marriage, as explained above. [If a married woman says]: "I will be forbidden [to eat] meat when I am divorced," her husband may nullify the vow. When she is divorced, she is permitted [to eat meat].30Here also, what is important is the woman's status at the time of the vow and not what her status will be when the vow takes effect.

הלכה יט
הַמְקַיֵּם בְּלִבּוֹ הֲרֵי זֶה קַיָּם. וְהַמֵּפֵר בְּלִבּוֹ אֵינוֹ מוּפָר כְּמוֹ שֶׁבֵּאַרְנוּ. לְפִיכָךְ אִם הֵפֵר בְּלִבּוֹ הֲרֵי זֶה יָכוֹל לַחְזֹר וּלְקַיֵּם. וְאִם קִיֵּם בְּלִבּוֹ אֵינוֹ יָכוֹל לַחְזֹר וּלְהָפֵר אֶלָּא אִם חָזַר בְּתוֹךְ כְּדֵי דִּבּוּר. כְּדֵי שֶׁלֹּא יִהְיֶה כֹּחַ דְּבָרִים שֶׁבְּלִבּוֹ גָּדוֹל מִכֹּחַ הַמּוֹצִיא בִּשְׂפָתָיו:
כסף משנה
19.
When a husband upholds [his wife's vow] in his heart, it has been upheld.31As stated in Chapter 12, Halachah 18, when a husband remains silent throughout the day, his wife's vow is upheld. This is a sign that his tacit acceptance of a vow is sufficient for it to be binding (Rabbenu Nissim). If he nullifies it in his heart, it is not nullified, as we explained.32As stated in Halachah 7, he must make a verbal statement of nullification. If, however, he voids his wife's vow, her nullification is not binding, as stated in Halachot 4-5. Therefore, if he nullifies it in his heart, he can still retract and uphold it. If, by contrast, he upheld it within his heart, he cannot retract and nullify unless he retracts immediately thereafter.33This term has a specific halachic definition: the time it takes a student to tell his teacher: Shalom Elecha Rabbi (Hilchot Sh'vuot 2:17). [That leniency is granted] so that his thoughts within his heart should not have greater power than the statements he makes.34Since a person can nullify a vow or an oath if he retracts within this time, he may certainly retract his acceptance of his wife's oath in thought.

הלכה כ
הַמְקַיֵּם נִדְרֵי בִּתּוֹ אוֹ אִשְׁתּוֹ וְנִחַם הֲרֵי זֶה נִשְׁאָל לְחָכָם וּמַתִּיר לוֹ הֲקָמָתוֹ וְחוֹזֵר וּמֵפֵר לָהּ בּוֹ בַּיּוֹם. אֲבָל אִם הֵפֵר לָהּ וְנִחַם אֵינוֹ יָכוֹל לְהִשָּׁאֵל לְחָכָם כְּדֵי שֶׁיַּחֲזֹר וִיקַיֵּם:
כסף משנה
20.
When a person upholds the vows of his daughter or his wife and then changes his mind, he may appeal to a sage to absolve him of his acceptance [of the vow].35I.e., just as he can appeal to a sage to absolve him of a vow he took, so, too, he may absolve his acceptance of a vow. He may then recant and nullify it for her that day.36I.e., the day he changed his mind, even if it is several days afterwards, is equivalent to the day he heard of his wife's vow. Since he cannot have his acceptance nullified unless he changes his mind, the days when he does not change his mind are considered equivalent to days when he does not know of the vow [Tur (Yoreh De'ah 234)].
There are other Rishonim who maintain that he can ask the sage to have his acceptance absolved only on the day he heard of the vow. The Shulchan Aruch (Yoreh De'ah 234:49) mentions both views without indicating which one should be favored. The Rama maintains that we should be stringent and follow the second view.
If, by contrast, he nullifies it for her and then changes his mind, he cannot appeal to a sage to absolve it so that he can retract and maintain it.37Upholding a vow is considered equivalent to taking a vow. Hence, just as a vow can be absolved, the acceptance of one can be absolved. The nullification of a vow, by contrast, cannot be considered as a vow and cannot be absolved. The Radbaz adds that if the person does not know that he can have his acceptance absolved, the day he finds out that information is equivalent to the day he heard of the vow.

הלכה כא
נַעֲרָה מְאֹרָסָה שֶׁנָּדְרָה וְקִיֵּם לָהּ אָבִיהָ לְבַדּוֹ אוֹ בַּעְלָהּ לְבַדּוֹ וְהֵפֵר לָהּ הָאַחֵר אַף עַל פִּי שֶׁנִּשְׁאַל לְחָכָם וְהִתִּיר לוֹ הֲקָמָתוֹ אֵינוֹ חוֹזֵר וּמֵפֵר לָהּ עִם הָאַחֵר שֶׁכְּבָר הֵפֵר לָהּ. שֶׁאֵין לָהֶם לְהָפֵר אֶלָּא שְׁנֵיהֶם כְּאֶחָד:
כסף משנה
21.
When a consecrated maiden takes a vow and only one of her father or husband upholds her vow, while the other nullifies, even if the one who upheld the vow approaches a sage and has his acceptance absolved, he cannot recant and nullify the vow38The Siftei Cohen 234:16 states that this applies even if he has the acceptance absolved on the day he hears of the vow. together with the one who has already nullified it. [The rationale is that] the two may only nullify [the vow] together.39Even if the first one nullified the vow again so that they make a combined statement, their nullification is not accepted.

הלכה כב
אָמַר לְבִתּוֹ אוֹ לְאִשְׁתּוֹ קַיָּם לִיךְ קַיָּם לִיךְ וְנִשְׁאַל עַל הֲקָמָה הָרִאשׁוֹנָה הֲרֵי הַשְּׁנִיָּה חָלָה עָלָיו. אָמַר לָהּ קַיָּם לִיךְ וּמוּפָר לִיךְ וְלֹא תָּחוּל הֲקָמָה אֶלָּא אִם כֵּן חָלָה הֲפָרָה הֲרֵי זֶה מוּפָר שֶׁאֵין הַהֲקָמָה מוֹעִיל אַחַר הַהֲפָרָה. אָמַר לָהּ קַיָּם וּמוּפָר לִיךְ בְּבַת אַחַת הֲרֵי זֶה קַיָּם. אָמַר לָהּ קַיָּם לִיךְ הַיּוֹם הֲרֵי זֶה קַיָּם לְעוֹלָם. אָמַר לָהּ מוּפָר לִיךְ לְמָחָר אֵינוֹ מוּפָר שֶׁהֲרֵי קִיְּמוֹ הַיּוֹם וּלְמָחָר אֵינוֹ יָכוֹל לְהָפֵר. אָמַר לָהּ קַיָּם לִיךְ שָׁעָה אַחַת וְעָבַר הַיּוֹם וְלֹא הֵפֵר הֲרֵי זֶה קַיָּם. וְאֵין אוֹמְרִין שֶׁזֶּה כְּמִי שֶׁאָמַר לָהּ הֲרֵי מוּפָר לִיךְ לְאַחַר שָׁעָה שֶׁהֲרֵי לֹא הוֹצִיא הֲפָרָה מִפִּיו. אָמַר לָהּ קַיָּם לֵיכִי שָׁעָה אַחַת וּכְשֶׁעָבְרָה הַשָּׁעָה אָמַר לָהּ מוּפָר לִיךְ הֲרֵי זֶה סָפֵק וּלְפִיכָךְ אֲסוּרָה בְּנִדְרָהּ. וְאִם עָבְרָה עַל נִדְרָהּ אֵינָהּ לוֹקָה:
כסף משנה
22.
If a man tells his daughter or his wife: "It is upheld for you. It is upheld for you," [even] if he asks to have the first acceptance absolved, the second one takes effect.40At the time he stated his acceptance of the vow a second time, his acceptance was of no consequence, because it was unnecessary. Nevertheless, after he nullifies his first acceptance, the second acceptance becomes significant.
If he tells her: "It is upheld for you. It is nullified for you, but the acceptance will not take effect until after the nullification does," [the vow] is nullified, because the acceptance does not take effect after the nullification.41As stated in Halachah 20.
If, however, he tells her: "It is upheld for you and nullified for you at the same time,"42The Radbaz states that this ruling applies even if he does not add the words "at the same time." it is upheld.43The two statements cancel each other out. It is as if he remained silent and the vow is therefore upheld. The Kessef Mishneh explains that the Rambam's rationale is that since the nullification cannot take effect after the vow is upheld, it cannot take effect if it is made simultaneously with the upholding of the vow. If he tells her: "It is upheld for you today," it is upheld forever.44Since, as the Rambam states later on, he did not verbally express his nullification of the vow, it remains binding even after the day passes. If he tells her: "It is nullified for you tomorrow," it is not nullified, for he upheld it today and he cannot nullify it on the following day.45For a vow must be nullified on the day, the man heard about it. In his Nekudot HaKessef, the Siftei Cohen explains that the Rambam's wording implies that he may nullify it that day. The Turei Zahav 234:39-40, however, infers that he cannot nullify it at all once it takes effect for that day. If he tells her: "It is upheld for you for one hour," and the day passed without him nullifying it, he has upheld it. We do not say that this is like one who said: "It is nullified for you after an hour," because he never verbally expressed its nullification.46The instances cited by the Rambam are questions posed by Nedarim 69b, 70a. Since the Talmud continues asking questions, using one instance as a springboard for another, following the pattern of im timtzeh lomar, the Rambam concludes that each of the instances used as a basis for a further question is accepted as halachah (Kessef Mishneh).
If he told her: "It is upheld for you for one hour," and after an hour, he told her: "It is nullified for you," there is an unresolved question [as to the ruling].47This is the last of the series of instances concerning which the Talmud asks in that passage. Therefore she is forbidden in [the matters] her vow [concerned].48Lest her vow in fact be binding. If, however, she violated her vow, she is not punished by lashes.49Because punishment is not given when we are uncertain whether a prohibition exists.

הלכה כג
מִי שֶׁנָּדַר נְדָרִים כְּדֵי לְכוֹנֵן דֵּעוֹתָיו וּלְתַקֵּן מַעֲשָׂיו הֲרֵי זֶה זָרִיז וּמְשֻׁבָּח. כֵּיצַד. כְּגוֹן מִי שֶׁהָיָה זוֹלֵל וְאָסַר עָלָיו הַבָּשָׂר שָׁנָה אוֹ שְׁתַּיִם. אוֹ מִי שֶׁהָיָה שׁוֹגֶה בַּיַּיִן וְאָסַר הַיַּיִן עַל עַצְמוֹ זְמַן מְרֻבֶּה. אוֹ אָסַר הַשִּׁכְרוּת לְעוֹלָם. וְכֵן מִי שֶׁהָיָה רוֹדֵף שַׁלְמוֹנִים וְנִבְהָל לְהוֹן וְאָסַר עַל עַצְמוֹ הַמַּתָּנוֹת אוֹ הֲנָיַת אַנְשֵׁי מְדִינָה זוֹ. וְכֵן מִי שֶׁהָיָה מִתְגָּאֶה בְּיָפְיוֹ וְנָדַר בְּנָזִיר וְכַיּוֹצֵא בִּנְדָרִים אֵלּוּ. כֻּלָּן דֶּרֶךְ עֲבוֹדָה לַשֵּׁם הֵם. וּבִנְדָרִים אֵלּוּ וְכַיּוֹצֵא בָּהֶן אָמְרוּ חֲכָמִים נְדָרִים סְיָג לִפְרִישׁוּת:
כסף משנה
23.
When a person takes vows in order to establish his character traits and correct his conduct, he is considered eager and praiseworthy. What is implied? If a person was a glutton and he [took a vow] forbidding meat for a year or two, a person was obsessed with wine and he [took a vow] forbidding himself from drinking wine for a prolonged period or he forbade himself from ever becoming intoxicated, a person would continually pursue illicit gain and was overexcited about wealth [took a vow] forbidding [accepting] presents or benefit from people in a particular country, similarly, a person who would be proud of his comely appearance and took a nazirite vow,50This requires him to allow his hair to grow untrimmed and thus will prevent him from beautifying his appearance. See Nedarim 9b which relates that Rabbi Shimon ben Shetach would almost never partake of the sacrifices of a nazirite. Once, however, he saw a particularly handsome young man who had taken a nazirite vow. He asked him why he had done so and the young man explained that, because of his good looks, he was being tempted by his evil inclination. To rise above the temptation, he took the nazirite vow. Rabbi Shimon ben Shetach praised him for his actions. or the like - all of these are paths in the service of God and concerning such vows and the like our Sages said:51Avot 3:13. "Vows are a safeguard for restraint."52In his commentary to that mishnah, the Rambam explains that "taking and maintaining vows to abstain from certain [undesirable] elements [of conduct] ingrains in a person the tendency to bridle the desires he seeks to curb. This tendency will continue and it will be easy for him to acquire the quality of restraint - i.e., the tendency to protect oneself from impurity." See also Moreh Nevuchim, Vol. III, the conclusion of ch. 48, which discusses the Divine service associated with taking and maintaining vows.
Nevertheless, the Rambam is not praising restraint as a mode of conduct that is always desirable. On the contrary, in Hilchot De'ot 3:1, he explains that a nazirite is called "a sinner" because he abstains from wine and states:

Our Sages directed man to abstain only from those things which the Torah denies him and not to forbid himself permitted things by vows and oaths. Thus our Sages (Jerusalem Talmud, Nedarim 9:1) asked rhetorically: "Are not the things which the Torah has prohibited sufficient for you? [Why] must you add further prohibitions?"

In the instances mentioned here, however, the person taking the vow is not doing so because he thinks that abstinence is desirable. Instead, he wishes to develop self-control and inner discipline and feels that taking a vow is an effective means to encourage him to do so.

הלכה כד
וְאַף עַל פִּי שֶׁהֵן עֲבוֹדָה (לַשֵּׁם) לֹא יַרְבֶּה אָדָם בְּנִדְרֵי אִסּוּר וְלֹא יַרְגִּיל עַצְמוֹ בָּהֶם. אֶלָּא יִפְרשׁ מִדְּבָרִים שֶׁרָאוּי לִפְרשׁ מֵהֶן בְּלֹא נֵדֶר:
כסף משנה
24.
Although [taking vows] is an element of the service of God, a person should not take many vows involving prohibitions and should not habituate himself to taking them.53Lest he not keep the vow, and in this way transgress. Instead, he should abstain from those things from which one should abstain without taking a vow.

הלכה כה
אָמְרוּ חֲכָמִים (גמרא נדרים נט א) "כָּל הַנּוֹדֵר כְּאִלּוּ בָּנָה בָּמָה". וְאִם עָבַר וְנָדַר מִצְוָה לְהִשָּׁאֵל עַל נִדְרוֹ כְּדֵי שֶׁלֹּא יְהֵא מִכְשׁוֹל לְפָנָיו. בַּמֶּה דְּבָרִים אֲמוּרִים בְּנִדְרֵי אִסָּר. אֲבָל נִדְרֵי הֶקְדֵּשׁ מִצְוָה לְקַיְּמָן וְלֹא יִשָּׁאֵל עֲלֵיהֶן אֶלָּא מִדֹּחַק שֶׁנֶּאֱמַר (תהילים קטז יד) (תהילים קטז יח) "נְדָרַי לַה' אֲשַׁלֵּם": סְלִיקוּ לְהוּ הִלְכוֹת נְדָרִים בְּסִיַעְתָּא דִּשְׁמַיָּא
כסף משנה
25.
Our Sages stated:54Nedarim 22a. "Anyone who takes a vow is considered as having built a private altar."55During the time the Sanctuary stood at Shilo and from the time the Temple was built in Jerusalem afterwards, it was forbidden to offer sacrifices on private altars. Similarly, taking a vow is considered undesirable and comparable to building such an altar. Rabbenu Nissim explains the comparison based on the passage from Hilchot De'ot cited above, i.e., just as a person who builds a private altar offers a sacrifice to God in an undesirable manner, so, too, a person who takes a vow adds a restriction that the Torah does not require him to observe. If he transgressed and took a vow, it is a mitzvah to ask [a sage] to absolve it,56As explained in ch. 4. so that he will not have an obstacle before him.
When does the above apply? With regard to vows involving prohibitions. With regard to vows involving the consecration of articles, it is a mitzvah to uphold them and not to ask for their absolution unless one is [financially] pressed, as [Psalms 116:14] states: "I will fulfill my vows to God."

הפלאה הלכות נדרים פרק יג
Haflaah Nedarim Chapter 13