Hilchot Nedarim

As the minutiae are great and the practicality of taking a Neder in Mishnaic Hebrew is not, it may be too confusing to attempt translating accurately into English. Hence, many specific cases and their discussions have been omitted.

Precautions and Circumstances for Taking Nedarim

General Warnings

1. One should not regularly take a Neder: even if he fulfills it, he is called a Rasha and sinner.
2. If one delays fulfilling a Neder, his account is "opened" in Heaven.
3. Taking a Neder is equivalent to building a Bamah at a time in which doing so is prohibited, and following through with it is equivalent to bringing a Korban on that Bamah. Instead, it's better he have it anulled. This is only true, however, with respect to regular Nedarim. It's actually a Mitzvah to fulfill Nidrei Hekdesh, and one should only attempt to anull them in very drastic situation.

Tzedaka

1. It's preferable to not even pledge Tzedaka in the form of a Neder. Rather, if he has the money, he should donate it right away. If he doesn't, it's better not to take the Neder until he does.
2. If one does have to pledge with the community, he should add "Bli Neder."

General Leniencies

1. One may take a Neder in a challenging, trying time ("Et Tzarah").
2. Nedarim and Shevuot may be taken as means of strengthening one's religious commitment, both in terms of fulfilling positive Mitzvot and evading the violation of negative ones.
3. However, one must be extremely careful when taking a Neder or Shevua in the context of Mitzvot, because even the more innocuous formulation will actually be binding.
4. Nedarim Siyag LePrishut: Taking a Neder to adjust one's personal attributes and tendencies is a form of serving Hashem. Examples include controlling one's extravagant appetite for meat and wine by taking a Neder against eating them for a period of time. Similarly, forbidding oneself from general indulgences is a means of bringing oneself to lesser focus on materialism. Nevertheless, one shouldn't become accustomed to taking Nidrei Issur (Prohibitive Nedarim). Instead, one should abstain from the actions and entities that he wishes to abstain from but without taking a Neder in the first place.

Formulating Nedarim

Ikar HaNeder & Hatfasah BaDavar HaNadur

1. The essential form of a Neder entails declaring that a permitted object be prohibited and be associated with an object which itself is the product of a previous vow (Davar HaNadur). For example, "This loaf of bread should be prohibited to me like a Korban," because a Korban is an inherently permitted animal that is sanctified via a Neder.
2. Similarly, if one already prohibited an object upon himself, he can then subsequently prohibit another object by associating it with this one. For example, "This loaf of bread should be prohibited to me like that one (which he already prohibited via a Neder)."
3. The associated object need not be a Korban, but, rather, it can be anything that is sanctified with one's speech.
4. If one hears his fellow declare a Neder and then himself says "And me like you!" within Toch Kedei Dibbur, he creates a bona fide Neder. This is true even if a hundred people follow, one at a time, each within Toch Kedei Dibbur of the last.

Hatfasah baDavar HaAssur (Inherently Prohibited Objects)

1. If one associated the object with an object that is inherently prohibited, such as a non Kosher animal or idol (Hatfasah baDavar HaAssur), the Neder is not binding on a Torah level. For example, declaring that "This meat should be prohibited unto me like pig meat" is ineffective.
2. Some argue that, on a rabbinic level, any such a Neder with association to an inherently prohibited object is effective on an Am HaAretz. Additionally, basic Charatah would be insufficient, and he would instead require a Petach from a different approach (MiMakom Acher) to annul it. Many others, however, argue that this stringency by Am HaAretz only applies when his ineffective Neder is taken to prohibit his wife unto him. This opinion also claims that, nowadays, everyone has the status of Am HaAretz.
3. The Chachamim did not impose their penalty in a case in which one was forced to take a Neder against his wife, and he associated her with an inherently prohibited object.
4. Granted an individual cannot declare his wine as "Yayin Nesech" or "Pat Akum" through a standard Neder, if he did it as a penalty to others for violating a stipulation he made, some claim it's effective, while others disagree.
5. A community can take punitive measures against members who act inappropriately and prohibit the objects of such individuals on others.

The Absence of Innumerable Specific Examples

1. There are many complicated minutia discussed in the Talmud and its commentaries regarding specific formulations of Nedarim, but they don't make it to the page of Shulchan Aruch for practical reasons.

Items Subject to Prohibition via Nedarim

1. One can declare a Neder on an item that is not yet in existence (Davar SheLo Ba LaOlam) to be prohibited once it comes into existence.

Yadot Nedarim

1. An incompletely formulated Neder, otherwise known as a Yad, can take effect just as a regular Neder does or it can not, depending on the level of ambiguity. If one's intention is mostly apparent (ידים מוכיחות), it is a valid Neder. That is to say, that if one says "I vow from you that I won't eat from you," (מודרני ממך שאיני אוכל לך) without saying "prohibited" or "Korban," it is nevertheless valid.
2. If the formulation is further lacking (ידים שאינן מוכיחות), i.e. it can be interpreted in more than one way, then some hold that we default to the most apparent interpretation, while others say the entire Neder is invalid.
3. If the formulation lacks any implication of a neder altogether, such as saying "That I won't ) it is not valid .
4. "I vow to you from eating and benefiting." (מודרני לך מאכילה או מהנאה) creates a Neder prohibiting eating and benefiting both ways between the one who took the vow and the one to whom he said it.
5. "I vow from you from eating and benefiting." (מודרני ממך...) only creates a one way prohibition on the one who took the vow receiving benefit from the one he said it to.
6. Due to the fact that wicked people are more oft to take Nedarim, one who takes a Neder "Like the vows of the wicked, this should be assur to me," (נדרי רשעים) it would be effective. Inversely, Tzaddikim never take Nedarim, so a Neder formulated on "Like the vows of Tzaddikim" (כנדרי צדיקים), would not be effective. However, Tzaddikim do volunteer Mitzvot, so a Neder formulated on "Nidvot Tzaddikim" (נדבות צדיקים), would be effective.

Neder Formulated as a Shevua

1. A Neder fundamentally differs from a Shevua in that a Neder is a prohibition that takes effect on the item vowed upon, while a Shevua takes effect on the person. As such, the subject of a Neder must be the item at hand ("This item should be prohibited to me"), and the subject of a Shevua must be the person ("It should be prohibited for me to do this action"). If a Neder is formulated in the language of a Shevua, there's is a great debate if it takes effect at all or at least on the level of a Yad, and many opine that it is ineffective, unless it's with respect to performing a Mitzvah. Nevertheless, because it has become commonplace to take Nedarim in such a language, one should not be lenient, lest people become even more lax with Nedarim.
2. Some argue that Nezirut is outside the scope of this discussion and would take effect regardless, while others disagree.

Kinui Nedarim

1. The Torah's mandate enabling one to take upon himself a Neder, Korban, Shevua, or Nezirut is not limited to the perfect pronunciation of the keywords (Neder, Korban, Shevua, and Nazir). Even a mispronunciation would take effect, given it's common to pronounce the word that way by some people in the place one is taking the Neder. For example, "Konam" could legitimately substitute for "Korban" in the time and communities of the Talmud. Gross mispronunciations (Kinuiyei Kinuiyim), however, are not effective.
2. The effectiveness of usage of the above keywords also depends on one's own understanding of them. If he doesn't understand what he's saying, his statement is invalid.

Miscellaneous

1. If one forgot if he took a Neder or if he took a Shevuah, he must act under the stringencies of both Nedarim and Shevuot. Similarly, if he isn't sure if he took a Shevuah in the first place, he must be stringent due to the uncertainty.