Nedarim, Chapter Three, Mishnah Two
The first section of the mishnah illustrates vows of exaggeration and the second illustrates vows that were made in error.
1) Vows of exaggeration:
a) If one says, Konam if I did not see on this road as many as departed from Egypt; If I did not see a snake [as thick as the] the beam of an olive press.
2) Vows in error:
a) [If one says, Konam,] if I ate or drank, and then remembered that he had;
b) If I eat or drink and then forgot [his vow] and ate or drank;
c) Konam be any benefit which my wife has from me, because she stole my purse or beat my child, and it was subsequently learnt that she had not beaten him nor stolen;
d) If one saw people eating [his] figs and said to them, Let the figs be a korban to you, and then discovered the people to be his father or his brothers.
i) If others were with them:
(1) Beth Shammai says: his father and brothers are permitted, but the rest are forbidden.
(2) Beth Hillel says: all are permitted.
Section one: Vows of exaggeration need not be kept, because the person did not really intend to take a vow. His only intention was to exaggerate.
Section two: This section teaches the important principle that vows made in error are invalid, and that a person has not broken his vow if he broke it in error. Furthermore, vows made based on false assumptions, such as that ones wife stole something or beat ones child, or the false presumption that people eating ones figs should not be eating them, are also invalid.
The final question in the mishnah is whether or not a vow can be half-valid, in other words valid with regard to some people and invalid with regard to others. In the case of the figs, both Beth Shammai and Beth Hillel agree that the brothers and father can eat, because the person who vowed intended to prohibit the figs only to strangers. However, Beth Shammai holds that the figs are prohibited to others who are there eating with them. Beth Hillel holds that since part of the vow isnt valid, the whole vow is invalid.