Last week’s parsha, Matos, opens with a discussion about vows, and the circumstances under which they may (or may not) be broken. The passage (Bamidbar 30:2-17) distinguishes between a neder (usually translated as “vow”) and a shvua (usually translated as “oath”). These seem like the same thing in English, but there is an important distinction between the two in halacha: a neder changes the status of some external thing, while a shvua initiates an internal change in the one who swears the oath. For example, if I swear that I will never again eat a burger, that’s a neder, because it changes the status of the burger from permitted to forbidden (but only for me, of course). But if I swear that I will learn a mishnah a day for the next year, that’s a shvua, because I’ve changed something within myself – I used to have the option of learning a mishnah a day or not, but now I’m required to learn a mishnah a day. Are you with me so far?
Now, here’s what puzzles me. I frequently hear people use the phrase “bli neder” when using language of promising – “I’ll be there at three, bli neder” or “I’ll call you after Shabbos, bli neder.” I’ve also seen people write “bli neder,” or simply b”n, after their name on Tehillim sign-up sheets and the like. Let’s assume, for simplicity’s sake, that it’s proper to say something like this to avoid the possibility of making an actual, binding vow. In all these examples, shouldn’t one say “bli shvua” instead? Clearly, these kinds of promises are of the second sort – the sort that creates a new internal obligation, rather than changing the status of an external object. So why is it that the phrase “bli neder” – which is undoubtedly correct in some, but not most, circumstances – is so popular, while “bli shvua” – by far the more useful of the two – is totally neglected?