Silence is an affirmation of a Neder and not an annulment of a Neder.
An affirmation in the heart is valid but an annulment in the heart is not valid.
Once the husband affirms the Neder he may not annul it and once he annuls it he may not affirm it.
A person may be released from an affirmation but not from an annulment of a Neder. (1)
If a husbandís silence to the Neder of his wife is because he wants to distress her it is a valid affirmation of the Neder.
Even if the wife makes a Neder at the end of the day the Neder may only be annulled until dark.
If the husband heard the Neder but he did not know that he was allowed to annul the Neder he may annul the Neder at a later day. (2)
R. Meir says that if the husband heard the Neder but didnít know that the Lashon that she used is regarded as a Neder he may not annul the Neder after that day. (3)
A husband may annul Nedarim that cause discomfort such as a Neder prohibiting washing or using cosmetics.
R. Yosi says that a Neder prohibiting washing or using cosmetics is not regarded as a Neder of Inuy Nefesh. (4)
R. Yosi says that a husband may not annul a Neder prohibiting the fruit of one Medinah or prohibiting the fruit of one storekeeper. (5)
A husband may annul a Neder of Inuy Nefesh and a Neder of Devarim Beino l'Beinah.
R. Yochanan Ben Nuri says that if a wife makes a Neder prohibiting her handiwork on her husband he shall annul it because of the possibility that he will divorce her and remarry her. (6)
A Neder of Inuy Nefesh may be completely annulled but a Neder of Devarim Beino l'Beinah may only annulled for himself not for a different husband.
A BIT MORE
1. A person may go to a Chacham and have his affirmation released but he may not have an annulment released.
2. When he finds out that he is allowed to annul the Neder of his wife he may annul the Neder that day.
3. The Chachamim hold that when the husband finds out that the Lashon that she used is a Neder he may annul the Neder on that day.
4. Instead it is regarded as a Neder of Beino l'Beinah. A Neder of Inuy Nefesh according to R. Yosi is a Neder prohibiting her from eating the fruit of the world.
5. If that particular storekeeper is the only one that extends them credit he may annul the Neder since they will not be able to buy fruit anywhere else.
6. Although the Neder is not effective since her handiwork belongs to her husband however if he divorces her the Neder will go into effect and if he remarries her the handiwork will remain forbidden to him.