When a young, unmarried woman living in her father's household takes a vow or accepts a personal prohibition, her father is granted the authority to intervene. If he becomes aware of her commitment and chooses to remain silent without expressing any objection, his silence serves as a binding legal endorsement, bringing the vow into full effect.
The way a father learns of the vow has specific parameters. The primary approach among commentators is that he does not need to hear the declaration directly from his daughter; being informed by others is sufficient [רלב״ג, חזקוני, תורה תמימה, מלבי״ם]. However, he must possess the physical ability to hear; a deaf father cannot legally uphold or annul his daughter's vows [בעל הטורים, תורה תמימה, מלבי״ם]. Furthermore, he must know the exact details of her commitment. If he operates under a misunderstanding—such as believing she swore off figs when she actually swore off grapes, or assuming she vowed to bring an offering when she actually took a Nazirite vow—his silence or intervention is entirely invalid. He cannot rely on general assumptions; his legal authority only activates once he comprehends precisely what she vowed [תורה תמימה].
The father's silence must also be consciously directed toward his daughter. If he overhears a vow but mistakenly assumes his wife made it, or fails to realize the speaker was his daughter, his lack of response does not validate the vow. In such cases, he retains the right to annul it the moment the truth becomes clear [רלב״ג, תורה תמימה, מלבי״ם]. For his silence to constitute absolute approval, he must refrain from objecting until the end of the natural day, marked by sunset [רש״ר הירש].
There is a discussion regarding which types of vows fall under the father's jurisdiction. The primary approach among commentators is that his authority is limited, much like a husband's, to vows that involve self-affliction and threaten her physical well-being, or commitments that would damage their interpersonal relationship. This limitation serves as a preparation for her future life as a married woman. In contrast, another perspective maintains that a father possesses absolute, unrestricted authority to annul any vow his daughter makes, regardless of its nature [רש״ר הירש].
The laws governing these vows also address their complexity and finality. A single vow might encompass multiple specific prohibitions, such as swearing off both figs and grapes simultaneously. In such complex cases, upholding or annulling one specific detail can have profound implications for the status of the entire vow [אור החיים]. Ultimately, the father's decision is absolute. If he approves and upholds the vow even for a single moment, it remains permanently binding, and he forever loses the right to retract his approval and annul it at a later time [תורה תמימה, מלבי״ם].