The Laws Governing Vows and Oaths
4. Should a person desire to establish a fixed period for the study of
Torah or desire to perform a particular mitzvoh, and fear that he will
alter fail to do so out of laziness; alternatively, should he fear that the
evil inclination will tempt him to transgress a prohibition or prevent him
from doing a mitzvoh, he is permitted to spur his determination by making a
vow or oath. [Nedorim 8a] quotes Rav as saying:
What is the source which teaches that one may make an oath to fulfill a
mitzvoh to spur his determination, even though he is bound by the oath made
at Mount Sinai? [Psalms 119:106 states]: "I have sworn and I will fulfill
[my oath] to observe your righteous commandments."
Even if one did not make such a statement in the form of an oath or vow,
but merely made a promise, it is considered to be a vow and he is obligated
to carry it out. Therefore, whenever a person makes a commitment to fulfill
a mitzvoh, he should always say "Bli neder" (without obligating myself
through a vow). It is proper for a person to train himself to add that
phrase even when promising to do matters of a secular nature, so that,
Heaven forbid, he will not err and transgress the prohibitions concerning vows.
5. A person who makes vows in order to rectify his character traits is
considered meticulous and praiseworthy; e.g., a glutton who took an oath
not to eat meat for a specific period, a drunkard who forbade for himself
the drinking of wine or other alcoholic beverages, a vain person -
preoccupied with his appearance - who vowed to be a Nazirite. Vows of this
nature are aspects of the service of G-d, blessed be His name, and
concerning such oaths, [Ovos 3:13] teaches: " Vows are a curb for
abstinence." Nevertheless, a person should not become accustomed to making
even such vows. Rather, he should attempt to control his desires without vows.
6. A vow does not take effect unless one's statements reflect the
intentions of one's heart. However, if one erred when making a vow and
intended to make a different statement from what he actually said - or
thought about making a vow, but did not make a statement to that effect -
it is not considered a vow.