Halacha

הלכה א
אַרְבָּעָה דְּבָרִים יֵשׁ בֵּין נְדָרִים לִשְׁבוּעַת בִּטּוּי. שֶׁבִּשְׁבוּעַת בִּטּוּי אֵין שְׁבוּעָה חָלָה עַל שְׁבוּעָה. וּבִנְדָרִים יָחוּל נֵדֶר עַל נֵדֶר. הַמַּתְפִּיס בִּשְׁבוּעָה פָּטוּר וּבִנְדָרִים חַיָּב. אֵין שְׁבוּעַת בִּטּוּי חָלָה אֶלָּא עַל דִּבְרֵי הָרְשׁוּת. וּנְדָרִים חָלוֹת עַל דִּבְרֵי מִצְוָה כְּדִבְרֵי הָרְשׁוּת. שְׁבוּעַת בִּטּוּי חָלָה עַל דָּבָר שֶׁיֵּשׁ בּוֹ מַמָּשׁ וְעַל דָּבָר שֶׁאֵין בּוֹ מַמָּשׁ. וּנְדָרִים אֵינָן חָלִין אֶלָּא עַל דָּבָר שֶׁיֵּשׁ בּוֹ מַמָּשׁ:
כסף משנה
1.
There are four differences between a vow and a sh'vuat bitui:
a) With regard to a sh'vuat bitui, one oath cannot take effect while another is already in effect,1See Hilchot Sh'vuot 4:9-10. The reverse ruling with regard to vows is described in Halachah 2. and with regard to vows, a vow can take effect while another is already in effect.
b) When one attempts to extend the scope of an oath taken previously, he is not liable,2See Hilchot Sh'vuot 2:8-9. The reverse rulings with regard to vows are described in Halachot 3-5. and with regard to vows, one is.
c) A sh'vuat bitui can take effect only with regard to actions that are left to one's choice,3See Hilchot Sh'vuot 5:14-16. The reverse ruling with regard to vows is described in Halachot 6-9. while vows take effect with regard to mitzvot as well as actions that are left to one's choice.
d) A sh'vuat bitui can take effect with regard to an entity of substance and an entity that is not of substance, 4This concept can be explained as follows: As stated in Halachah 6, an oath creates a prohibition on the person taking the oath (the gavra), i.e., the article is essentially permitted, he has accepted a prohibition on himself not to partake of it. Hence, it is not significant whether the article is of substance or not. With regard to vows, by contrast, the article itself (the cheftzah) becomes forbidden. Hence, for that prohibition to take effect, the article must be of substance (Radbaz). See Halachah 10 for an illustration of how this principle is effective with regard to vows. while vows take effect only with regards to entities of substance.

הלכה ב
כֵּיצַד יָחוּל נֵדֶר עַל נֵדֶר. הָאוֹמֵר הֲרֵי עָלַי קָרְבָּן אִם אָכַלְתִּי כִּכָּר זוֹ. הֲרֵי עָלַי קָרְבָּן אִם אֹכָלֶנָּה וַאֲכָלָהּ חַיָּב עַל כָּל אַחַת וְאַחַת. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
2.
What is meant by the statement that a vow can take effect while another is already in effect? If a person says: "I will be obligated to bring a sacrifice if I eat this loaf [of bread]," [repeats]: "I will be obligated to bring a sacrifice if I eat it," he is liable [to bring a sacrifice] for every vow that he takes. Similar laws apply in all analogous situations.

הלכה ג
כֵּיצַד הַמַּתְפִּיס בִּנְדָרִים חַיָּב. שָׁמַע חֲבֵרוֹ שֶׁנָּדַר וְאָמַר וַאֲנִי כְּמוֹתְךָ בְּתוֹךְ כְּדֵי דִּבּוּר הֲרֵי זֶה אָסוּר בְּמַה שֶּׁנֶּאֱסַר בּוֹ חֲבֵרוֹ. שָׁמַע הַשְּׁלִישִׁי זֶה שֶׁאָמַר וַאֲנִי וְאָמַר וַאֲנִי אֲפִלּוּ הָיוּ מֵאָה וְכָל אֶחָד מֵהֶן אוֹמֵר וַאֲנִי בְּתוֹךְ כְּדֵי דִּבּוּרוֹ שֶׁל חֲבֵרוֹ הֲרֵי כֻּלָּן אֲסוּרִין:
כסף משנה
3.
What is meant by the statement that one who extends the scope of a vow taken previously is liable? He heard his colleague take a vow and said: "And I am like you" immediately thereafter,5This term refers to a specific span of time, the time it takes to say: Shalom Elecha Rebbi (Hilchot Sh'vuot 2:17). he is forbidden [to partake of] the substance that his colleague deemed forbidden.6I.e., he is extending the scope of his colleague's vow, so that it includes not only his colleague, but he himself.
Here also the concept can be explained according to the above difference. Since an oath involves an obligation on the person taking the oath (gavra), it cannot be extended to include another individual, for each person must take his own oath. With regard to a vow, by contrast, since the prohibition caused by the vow is associated with a substance (cheftzah), another person can also extend the prohibition to himself (Rabbenu Nissim).
If a third person heard the second person say: "And I am like you," and he also said: "I am like you," [he is also forbidden]. Even if there are one hundred and each one says: "And I am like you" immediately thereafter the statements of the previous one," they are all forbidden.

הלכה ד
וְכֵן הָאוֹמֵר הַבָּשָׂר הַזֶּה עָלַי אָסוּר וְחָזַר וְאָמַר אֲפִלּוּ אַחַר כַּמָּה יָמִים וְהַפַּת הַזֹּאת כַּבָּשָׂר הַזֶּה הֲרֵי הַפַּת נִתְפְּשָׂה וְנֶאֶסְרָה. חָזַר וְאָמַר וּדְבַשׁ זֶה כַּפַּת הַזֹּאת וְיַיִן זֶה כִּדְבַשׁ זֶה אֲפִלּוּ הֵן מֵאָה כֻּלָּן אֲסוּרִין:
כסף משנה
4.
Similarly, when one says: "This meat is considered forbidden to me,' and even after several days7In this instance, it is not necessary to make the statement immediately thereafter the first vow. Since the meat is visible before us, one can attach a vow to it. With regard to the previous halachah, by contrast, we are speaking about a subject that cannot be seen. Hence, unless the statements are made immediately after each other, there is no way we can be certain of the meaning of the statement: "And I am like you" (Radbaz). says: "This bread is like this meat," [the prohibition] is extended to the bread and it becomes forbidden. If afterwards, he said: "And this honey is like this bread, and this wine is like this honey," even if he mentions 100 [substances], they are all forbidden.

הלכה ה
הֲרֵי שֶׁמֵּת אָבִיו אוֹ רַבּוֹ הַיּוֹם וְנָדַר שֶׁיָּצוּם אוֹתוֹ הַיּוֹם וְצָם. וּלְאַחַר שָׁנִים אָמַר הֲרֵי יוֹם זֶה עָלָיו כְּיוֹם שֶׁמֵּת בּוֹ אָבִיו אוֹ רַבּוֹ הֲרֵי זֶה אָסוּר לֶאֱכל בּוֹ כְּלוּם שֶׁהֲרֵי הִתְפִּיס יוֹם זֶה וַאֲסָרוֹ כַּיּוֹם הָאָסוּר לוֹ. וְכֵן כָּל כַּיּוֹצֵא בְּאֵלּוּ:
כסף משנה
5.
[The following rules apply when a person's] father or teacher died on a particular day and he took a vow to fast that day8This is a common practice in many communities. and [actually] fasted.9If, however, he never fasted on that day, he cannot attach another day to this vow (Chazon Yechezkel). If after years passed, he said: "Let this day10I.e., any given day. be considered as the day on which my father - or my teacher - died," he is forbidden to eat on that day. For he attached this day [to his existing vow] and caused it to be forbidden as the day which is forbidden for him. Similar laws apply in all analogous situations.

הלכה ו
כֵּיצַד חָלִים הַנְּדָרִים עַל דִּבְרֵי מִצְוָה כְּדִבְרֵי הָרְשׁוּת. הָאוֹמֵר הֲרֵי הַמַּצָּה בְּלֵילֵי הַפֶּסַח אֲסוּרָה עָלָיו. הֲרֵי יְשִׁיבַת הַסֻּכָּה בֶּחָג הַסֻּכּוֹת אֲסוּרָה עָלָיו וַהֲרֵי הַתְּפִלִּין אֲסוּרוֹת בִּנְטִילָה עָלָיו הֲרֵי אֵלּוּ אֲסוּרִין עָלָיו. וְאִם אָכַל אוֹ יָשַׁב אוֹ נָטַל לוֹקֶה. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה. וְאֵין צָרִיךְ לוֹמַר בְּמִי שֶׁאָמַר הֲרֵי עָלַי קָרְבָּן אִם אֹכַל מַצָּה בְּלֵילֵי הַפֶּסַח שֶׁהוּא חַיָּב בְּקָרְבָּן. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
6.
What is meant by the statement that vows take effect with regard to mitzvot as well as actions that are left to one's choice? When a person says: "Matzah is forbidden to me on Pesach night," "Dwelling in a sukkah on that holiday is forbidden to me," or "I am forbidden to take hold of tefillin," they are forbidden to him. If he ate matzah, dwelled in a sukkah, or took tefillin, he is liable for lashes.11For breaking his vow. The Rama (Yoreh De'ah 215:1) mentions a view that maintains that the person should be given corporal punishment for taking such a vow and should be compelled to ask to have the vow released. Similar laws apply in all analogous situations. Needless to say, one who says: "I am obligated to bring a sacrifice if I eat matzah on Pesach night," is obligated to bring a sacrifice.12For he can fulfill the mitzvah and bring the sacrifice (the Rambam's Commentary to the Mishnah, Nedarim 2:2). Similar laws apply in all analogous situations.

הלכה ז
וּמִפְּנֵי מָה נְדָרִים חָלִים עַל דִּבְרֵי מִצְוָה וּשְׁבוּעוֹת אֵין חָלוֹת עַל דִּבְרֵי מִצְוָה. שֶׁהַנִּשְׁבָּע אוֹסֵר עַצְמוֹ עַל דָּבָר שֶׁנִּשְׁבַּע עָלָיו. וְהַנּוֹדֵר אוֹסֵר הַדָּבָר הַנָּדוּר עַל עַצְמוֹ. נִמְצָא הַנִּשְׁבָּע לְבַטֵּל מִצְוָה אוֹסֵר עַצְמוֹ וּכְבָר עַצְמוֹ מֻשְׁבָּע מֵהַר סִינַי וְאֵין שְׁבוּעָה חָלָה עַל שְׁבוּעָה. וְהָאוֹסֵר דָּבָר זֶה בְּנֵדֶר זֶה הַדָּבָר הוּא שֶׁנֶּאֱסַר וְאוֹתוֹ הַדָּבָר אֵינוֹ מֻשְׁבָּע מֵהַר סִינַי:
כסף משנה
7.
Why do vows take effect with regard to mitzvot and oaths do not take effect with regard to mitzvot? Because when a person takes an oath he forbids himself from [partaking of] the entity mentioned in the oath.13I.e., the prohibition involves the gavra, the person himself. It cannot take effect if he is already bound to act otherwise. When, by contrast, one takes a vow, he causes the entity mentioned in the vow to be forbidden to him.14I.e., the prohibition involves the cheftzah, the article. Once it is forbidden, it is forbidden to fulfill the mitzvah by partaking of it or using it, for a positive commandment does not supercede a negative commandment. It would be a mitzvah fulfilled through a transgression which is a forbidden act (the Rambam's Commentary to the Mishnah, loc. cit.). Thus when a person takes an oath to nullify a mitzvah, he is placing a prohibition upon himself and he is already bound by an oath [to observe that mitzvah] from Mount Sinai, and one oath does not take effect if another is already in effect. When, by contrast, a person causes an entity to be forbidden through a vow, the prohibition involves the entity itself and that entity is not under oath from Mount Sinai.

הלכה ח
כְּשֶׁאַתָּה מִתְבּוֹנֵן בַּכָּתוּב תִּמְצָא שֶׁהַדְּבָרִים מַרְאִין כֵּן כְּמוֹ שֶׁקִּבְּלוּ חֲכָמִים מִפִּי הַשְּׁמוּעָה. שֶׁהֲרֵי אוֹמֵר בִּשְׁבוּעַת בִּטּוּי (ויקרא ה ד) "לְהָרַע אוֹ לְהֵיטִיב" בְּדִבְרֵי הָרְשׁוּת כְּמוֹ שֶׁבֵּאַרְנוּ. שֶׁיֹּאכַל וְיִשְׁתֶּה הַיּוֹם אוֹ שֶׁיָּצוּם וְכַיּוֹצֵא בָּהֶן. וּבִנְדָרִים הוּא אוֹמֵר (במדבר ל ג) "כְּכָל הַיֹּצֵא מִפִּיו יַעֲשֶׂה" וְלֹא חִלֵּק בֵּין דִּבְרֵי מִצְוָה לְדִבְרֵי הָרְשׁוּת:
כסף משנה
8.
When you contemplate [the wording of] the Torah, it appears that their interpretation matches the explanation which our Sages received according to the Oral Tradition. For with regard to a sh'vuat bitui, [Leviticus 5:4] states: "Whether he will do harm or do good," i.e., speaking about permitted activities as we explained,15Hilchot Sh'vuot 5:16. e.g., whether I will eat or drink today, whether I will fast, or the like. With regard to vows, by contrast, [Numbers 30:3] states: "He shall do everything uttered by his mouth," without differentiating between matters associated with mitzvot and those left to our own volition.

הלכה ט
הַנּוֹדֵר שֶׁיָּצוּם בְּשַׁבָּת אוֹ בְּיוֹם טוֹב חַיָּב לָצוּם. שֶׁהַנְּדָרִים חָלִים עַל דִּבְרֵי מִצְוָה כְּמוֹ שֶׁבֵּאַרְנוּ. וְכֵן הַנּוֹדֵר שֶׁיָּצוּם יוֹם רִאשׁוֹן אוֹ יוֹם שְׁלִישִׁי כָּל יָמָיו וּפָגַע בּוֹ יוֹם זֶה וַהֲרֵי הוּא יוֹם טוֹב אוֹ עֶרֶב יוֹם הַכִּפּוּרִים הֲרֵי זֶה חַיָּב לָצוּם וְאֵין צָרִיךְ לוֹמַר רֹאשׁ חֹדֶשׁ. פָּגַע בּוֹ חֲנֻכָּה וּפוּרִים יִדָּחֶה נִדְרוֹ מִפְּנֵי הַיָּמִים הָאֵלּוּ הוֹאִיל וְאִסּוּר הַצּוֹם בָּהֶם מִדִּבְרֵי סוֹפְרִים הֲרֵי הֵן צְרִיכִין חִזּוּק וְיִדָּחֶה נִדְרוֹ מִפְּנֵי גְּזֵרַת חֲכָמִים:
כסף משנה
9.
When a person takes a vow to fast on the Sabbath or a festival, he is obligated to fast16Despite the fact that by doing so he negates the mitzvah of taking pleasure in the Sabbath and festivals. The Ra'avad clarifies that the matter is dependent on the wording he used in his oath. If on the Sabbath, he said: "I will fast today," he is forbidden to keep his vow. for vows take effect even when they involve [the nullification of] a mitzvah as explained.17In the three preceding halachot. Similarly, if a person takes an oath to fast every Sunday or every Tuesday throughout his life and a festival or the day preceding Yom Kippur18When it is a mitzvah to eat in preparation for the fast (Rosh HaShanah 9a; Shulchan Aruch, Orach Chayim 604:1). falls on that day, he is obligated to fast. Needless to say, this applies with regard to Rosh Chodesh. If, however, Chanukah or Purim fall [on these days], his vow is superceded by [the celebrations of] these days. Since the prohibition against fasting on them is based on Rabbinic decree, reinforcement is necessary.19In contrast to the Sabbath and festivals where the obligation to eat is of Scriptural origin. This is a general principle in Talmudic Law. There are times when our Sages gave their decrees greater power than Scriptural Law, for Scriptural Law is revered by the people at large and does not require reinforcement. If, by contrast, Rabbinic Law was abrogated in such instances, it might lead people to take leniencies even when uncalled for (see Ta'anis 17b; Kessef Mishneh). The Radbaz explains that if keeping one's vow was allowed to override a Rabbinic decree, then there would be no point in making such decrees. For people could nullify them by taking vows. For example, a person could take a vow to drink ordinary gentile wine.
The Kessef Mishneh also explains that although the obligation to eat on Rosh Chodesh and the day preceding Yom Kippur is also of Rabbinic origin, since our Sages found an allusion to it in the Torah, it is less likely that people will treat it lightly.
Hence, his vow is superceded by the Rabbinic decree.

הלכה י
כֵּיצַד אֵין הַנְּדָרִים חָלִים אֶלָּא עַל דָּבָר שֶׁיֵּשׁ בּוֹ מַמָּשׁ. הָאוֹמֵר דִּבּוּרִי עָלֶיךָ קָרְבָּן אֵינוֹ אָסוּר מִלְּדַבֵּר עִמּוֹ שֶׁהַדִּבּוּר אֵין בּוֹ מַמָּשׁ. וְכֵן אִם אָמַר לוֹ דִּבּוּרִי אָסוּר עָלֶיךָ אֵין זֶה כְּאוֹמֵר פֵּרוֹתַי אֲסוּרִין עָלֶיךָ אוֹ פֵּרוֹתַי קָרְבָּן עָלֶיךָ שֶׁהֵן אֲסוּרִין עָלָיו. לְפִיכָךְ הָאוֹמֵר לַחֲבֵרוֹ קָרְבָּן שֶׁאֵינִי מְדַבֵּר עִמְּךָ אוֹ שֶׁאֵינִי עוֹשֶׂה עִמְּךָ אוֹ שֶׁאֵינִי מְהַלֵּךְ עִמְּךָ. אוֹ שֶׁאָמַר קָרְבָּן שֶׁאֵינִי יָשֵׁן שֶׁאֵינִי מְדַבֵּר שֶׁאֵינִי מְהַלֵּךְ. אוֹ שֶׁאָמַר לְאִשְׁתּוֹ קָרְבָּן שֶׁאֵינִי מְשַׁמְּשֵׁךְ אֵין הַנֵּדֶר חָל בְּכָל אֵלּוּ. וַהֲרֵי זֶה כְּאוֹמֵר דִּבּוּרִי וְהִלּוּכִי וַעֲשִׂיָּתִי וְשִׁמּוּשִׁי קָרְבָּן שֶׁהֵן דְּבָרִים שֶׁאֵין בָּהֶן מַמָּשׁ:
כסף משנה
10.
What is meant by the statement that vows take effect only with regards to entities of substance? If one says: "My speech is like a sacrifice for you,"20I.e., he takes a vow against the other person listening to his speech. he is not forbidden to speak to him, because speech is not an entity of substance. Similarly, if he tells him: "My speech is forbidden to you," it is not like his saying: "my produce is forbidden to you," or "My produce is like a sacrifice for you," in which instance, [the produce] would be forbidden.
Therefore, if a person tells a colleague: "[It is like a vow for] a sacrifice that I will not speak with you," "...that I will not act on your behalf," or "...that I will not go with you," or he told his wife, "[It is like a vow for] a sacrifice that I will not be intimate with you," his vow does not take effect in all these instances. For this is as if he is saying: "My speech, going, actions, or intimacy is like a sacrifice, and none [of these are] entities of substance.21If, however, he states: "The satisfaction that I receive from any of the above is forbidden," his vow is effective, for the satisfaction is considered substantial. See Chapter 12, Halachah 9.

הלכה יא
אֲבָל הָאוֹמֵר יֵאָסֵר פִּי לְדִבּוּרוֹ וְיָדַי לְמַעֲשֵׂיהֶן וְרַגְלַי לְהִלּוּכָן וְעֵינַי לִשְׁנָתָן הֲרֵי הַנֵּדֶר חָל עֲלֵיהֶן. לְפִיכָךְ הָאוֹמֵר לַחֲבֵרוֹ קָרְבָּן פִּי מִלְּדַבֵּר עִמְּךָ וְיָדַי מִלַּעֲשׂוֹת עִמְּךָ וְרַגְלַי מִלְּהַלֵּךְ עִמְּךָ הֲרֵי זֶה אָסוּר. וְכֵן הָאוֹמֵר הֲרֵי עָלַי קָרְבָּן אִם אֲדַבֵּר עִם פְּלוֹנִי אוֹ אִם לֹא אֲדַבֵּר עִמּוֹ וְעָבַר עַל דְּבָרוֹ חַיָּב בְּקָרְבָּן. וְכֵן אִם נָדַר דִּבַּרְתִּי וְלֹא דִּבַּרְתִּי וְכַיּוֹצֵא בָּהֶן שֶׁאֵין אֵלּוּ נִדְרֵי אִסָּר שֶׁאָנוּ מְבָאֲרִין מִשְׁפְּטֵיהֶם אֶלָּא נִדְרֵי הֶקְדֵּשׁ:
כסף משנה
11.
When, by contrast, a person says: "Let my mouth be forbidden to speak, my hands to act, my feet to walk, and my eyes to sleep," his vow is effective with regard to them.22For these organs are objects of substance (Nedarim 13b). Therefore if a person tells a colleague: "My mouth is like a sacrifice with regard to speaking with you, my hands [are so] with regard to acting on your behalf, and my feet [are so] with regard to going with you," he becomes forbidden.
Similarly, one who tells a colleague: "I will be obligated to bring a sacrifice if I speak to so-and-so" or "...if I don't speak to so-and-so," he is obligated to bring a sacrifice if he violates this commitment. Similarly, if he took a vow in which he said: "[If] I spoke [to so-and-so, I must bring a sacrifice]" or "[If] I did not speak..." or the like, [he is liable]. For these are not vows in which he accepts prohibitions upon himself23And apply only to entities of substance. whose ground rules we are explaining here, but vows of dedication.24Which are described in Hilchot Ma'aseh HaKorbanot, chs. 6 and 9. See also Chapter 1 where the Rambam makes a distinction between these two types of vows.

הלכה יב
הַנּוֹדֵר בִּדְבָרִים שֶׁאֵין בָּהֶם מַמָּשׁ וַאֲסָרָן אַף עַל פִּי שֶׁאֵין הַנֵּדֶר חָל עֲלֵיהֶם אֵין מוֹרִים לוֹ שֶׁיִּנְהֹג בָּהֶן הֶתֵּר הוֹאִיל וְאָסַר עַצְמוֹ בָּהֶן וּבְדַעְתּוֹ שֶׁהַנֵּדֶר חָל עֲלֵיהֶן. אֶלָּא פּוֹתְחִין לוֹ פֶּתַח מִמָּקוֹם אַחֵר וּמַתִּירִין לוֹ נִדְרוֹ אַף עַל פִּי שֶׁלֹּא נֶאֱסַר כְּדֵי שֶׁלֹּא יִנְהֲגוּ קַלּוּת רֹאשׁ בִּנְדָרִים:
כסף משנה
12.
Although when a person takes a vow concerning entities that are not of substance and forbids them, the vow does not take effect with regard to them, we do not rule that he should act as if they are permitted. [Instead,] since he willingly [took a vow] forbidding them to him, [according to Rabbinic decree]25See Nedarim 15a. Similarly, in his Commentary to the Mishnah (Nedarim 2:1), the Rambam writes that the prohibition against desecrating one's word applies with regard to these vows. Compare to Chapter 4, Halachah 4. the vow took effect with regard to them. Although they are not forbidden, we give him an opportunity [to ask for the vow's release] from another vantage point and then release the vow, so that he will not act frivolously with regard to vows.26See Chapter 2, Halachot 12-13.

הפלאה הלכות נדרים פרק ג
Haflaah Nedarim Chapter 3