In this mitsvah, Rambam takes what could have been a narrow, technical mitsvah and gives it broader ethical ramifications. In its original context, the relevant verses, one in Parshat Matot and the other in Ki Tetsei, warn one who makes a neder (a vow, as we will discuss) to fulfill it. In Matot, the Torah says, ke-khol hayotsei mi-piv ya`aseh, he should do whatever comes out of his mouth, while in Ki Tetsei the verse says motsa sefatekha tishmor, you should keep that which your lips emit. Rambam connects the two verses, saying that they are meant as a general obligation to fulfill whatever we accept upon ourselves, whether a sacrifice, a neder, a shevu`ah, or even just a promise to give tsedakah.

We might have thought that he meant to expand that to any verbal commitment, but he does not go that far. Whatever falls under one of the four categories mentioned, a fairly broad group, becomes obligatory on a de-oraita level. A sacrifice means that one verbally declares his intent to offer a particular animal as a sacrifice or to donate some object to the Temple creates a de-oraita obligation to follow through. A promise to give tsedakah works the same way- simply deciding to do so verbally (tsedakah may even work purely internally, although that is a different discussion) creates this obligation.

Neder and shevu`ah are slightly less clear terms, so let’s spend a moment on them. Shevu`ah refers to a shevu`at bitui, a shevu`ah in which a person accepts upon him/herself to either actively perform or to refrain from a certain action. One could, for example, declare one’s intention to eat a certain food the next day (or to refrain from that food) and create a de-oraita obligation to do so. As long as the verbal declaration fit the form of a shevu`at bitui—meaning it had the word shevu`ah or other similar words, as well as a direct mention of God’s Name, or sufficiently close references to the Creator—the verses mentioned above tell us that that person is now as obligated to fulfill his promise.

At the beginning of Hilkhot Nedarim, Rambam delineates two kinds of nedarim. The first, which we have already discussed, consists of those in which a person promises something to God or the Temple (a sacrifice or a donation that will support the upkeep of the House). The second, more common type, are those in which a person prohibits a certain item to oneself (as opposed to shevu`ah, which can also be used to obligate oneself to perform a certain act). There, too, the prohibition will take on both negative (Mitsvot Lo Ta`aseh 157) and positive de-oraita status.

Most surprisingly, Rambam defines these nedarim as not needing particular terminology, either in the word neder or a Divine Name. For Rambam, then, the statement "Apples will always be prohibited to me," qualifies as a neder, and the person will have to fulfill that declaration (on a de-oraita level) unless s/he finds a sage who is able to be matir the neder. Seeing that Rambam rules this way about nedarim, we can see a rationale, at least in the case of prohibitions, to say beli neder before a statement. If someone wants to say that eating a certain food will be prohibited to them, for example, saying beli neder would avoid the problem of having created an issur de-oraita according to Rambam.

Ramban objects to two elements of that presentation, significantly altering our picture of this mitsvah. First, he thinks Rambam conflated two separate mitsvot, one for each of the verses mentioned above. He sees the first as applying to general statements (such as a shevuah or a neder about ordinary actions), while the second only applies to nedarim that offer objects or money to hekdesh, the Temple and its properties. That seems to be a technical dispute about how to count the mitsvot of the Torah, which is surprising in light of Ramban’s views earlier in the Sefer haMitsvot.

Rambam opens up the Sefer haMitsvot with a discussion of how he went about enumerating them. One of his fundamental principles was that there were 613 total mitsvot, based on Talmudic statements. Ramban, in his gloss to that discussion, seems to say that he does not believe the number 613 is obligatory; one rabbi asserted that number, but he (Ramban) saw no reason to be ruled by it. Having said that, it is odd that he would choose to debate Rambam as to whether a certain mitsvah was one or two. I would suggest that the question of one or two mitsvot, certainly for Ramban and possibly for Rambam, indicates the level of relationship among two Torah ideas. In our case, Rambam, by taking these two mitsvot as one, lumps them together as cases where the Torah obligates us to carefully fulfill our word. Ramban, by distinguishing promises made to the Temple from those made in general, maintains that our conduct towards the Temple is a separate realm from ordinary conduct, and is always treated as such by the Torah.

Ramban raises a more substantive point when he claims that nedarim also need a specific language to be used. Where Rambam had said that a simple declaration of prohibition creates a neder, Ramban requires the language of a neder, or related terms, much as had been the case with shevu`ah. For Rambam, then, a neder consists of a decision to treat something as prohibited; for Ramban, it depends on a more formal declaration.

Rambam’s view of neder fits in nicely with his phrasing, that the Torah really wishes to obligate us to fulfill all the commitments we make. It is not primarily, then, an issue of a technical set of declarations with their various complicated rules, but just the desire to have us be careful with what we say, to have us take seriously the commitments we make with our mouths. Shabbat Shalom.