Kiddushin, Chapter Three, Mishnah Eight
The main topic discussed in this mishnah is when a man is believed with regard to statements he makes that impact his childrens personal status. The general rule is that a man is believed to say that he has done something which he currently has the legal ability to do. We shall see examples of this in the mishnah.
1) [If a man declares] I have given my daughter in betrothal, [or] I gave her in betrothal and divorced her while she was still a minor, and she is [now] a minor, he is believed.
2) I gave her in betrothal and divorced her while she was still a minor, and she is now of majority age, he is not believed.
3) She was taken captive and I redeemed her, whether she is a minor or of majority age he is not believed.
4) If a man declares at the time of his death I have sons, he is believed;
a) I have brothers, he is not believed.
5) If one betroths his daughter without specifying which, the daughters of majority age are not included.
Section one: As we have learned already, a man has the legal right to betroth his daughter before she reaches majority age. He also has the legal right to accept a get on behalf of his married daughter as long as she has not reached majority age. If the daughter about whom this father is testifying is now a minor, he is believed to say that he betrothed her, or that he betrothed her and then accepted her get, since he currently has the power to perform either activity. The ramification of his being believed to state that he accepted her get, is that she will be disqualified from subsequently marrying a priest.
Section two: If she is now an adult (past 12 1/2 years old), he is no longer believed if he makes these statements, since he no longer has the legal right to either accept betrothal or a get on her behalf. We should note that this limits the power of the father over his daughter. Once she is past a relatively young age, he has no legal right to make decisions regarding her kiddushin, nor can he make any statement which would severely impact her status.
Section three: A woman who was taken captive is forbidden from subsequently marrying a priest (see Ketubot 2:5). This is because it is assumed that her non-Jewish captors had sexual relations with her and a woman who has had intercourse with a non-Jew is forbidden from marrying a priest. The father is not believed if he states that his daughter was taken captive, no matter how old she is when he offers such testimony. A father does not have the legal right to give his daughter in marriage to a non-Jew and therefore he doesnt have any special right to testify about this having happened in order to thereby prohibit her to a kohen. Note that when she is a minor the father does have another means by which to prohibit his daughter to the priesthood; he can testify that he betrothed her and then accepted her divorce. Nevertheless, he does not have the right to testify that she was taken captive.
Section four: This section discusses a man who offers testimony which will impact his wifes subjectivity to the laws of yibbum. By stating that he has sons he is exempting her from yibbum. He is believed because if all he wanted to do was exempt her from yibbum he could divorce her. However, he is not believed to state that he has brothers, thereby obligating her for yibbum. Unless we know that he has brothers, he (or others) would have to bring evidence to make his wife subject to yibbum.
Section five: This section connects back to the previous mishnah as well as to the next mishnah. If a father states that he betrothed one of his daughters, but does not remember which one he betrothed, all of his minor daughters are in a state of possible betrothal, since he has the legal right to betroth any of them. None of them can marry until the matter is clarified. However, the girls who are of majority age are not doubtfully betrothed since the father has no legal right to betroth them.