Bli NederBy Rabbi Jack Abramowitz
Moshe told the heads of the Tribes the laws of vows. If a person makes a vow to G-d or takes an oath forbidding something to himself, he must fulfill his word.
If a girl still living in her father’s house makes a vow or an oath, her father can annul it. If he learns of it and does not object, he has given his tacit approval and she must keep her word. He has until nightfall on the day he learns of her vow or oath to annul it.
Next, the Torah speaks of a “betrothed” woman. Betrothal is more than engagement; it’s “half-married” and breaking off a betrothal would require a divorce. A betrothed woman’s vow or oath must be jointly annulled by both her fiancé and her father, since she has a foot in each one’s domain. On the other hand, a widow or divorcee has left her father’s house and no longer has a husband, so she must keep her vows and oaths “as is.”
When it comes to vows and oaths, a married woman’s husband has the same authority as her father had when she was single. He can annul it on the day he learns of it. If he doesn’t do so, he has given tacit approval and the oath or vow must be fulfilled.
The aliyah only speaks of a woman having her vows annulled by her father or husband. While not explicit in the text, vows could also be permitted by a Torah scholar or a beis din (ritual court) of commoners. (See Talmud Nedarim 78a.) Judaism takes oaths rather seriously, which is why Jews tend to “affirm” rather than “swear” in court and many are careful to say “bli neder” when making a tentative commitment, so as to ensure that their words do not have the force of a vow. (The Talmud in Gittin, 35a, relates a story in which disaster ensued when a widow thought she was swearing a vow truthfully, but she was mistaken. We try to avoid swearing altogether, just in case.)