Ketubot, Chapter Eleven, Mishnah Six
The last mishnah of our chapter deals with cases where a marriage was prohibited or was ended by the wifes refusal of the marriage or by her being found to be an aylonit. To remind ourselves, a girl who is married off by her brothers or mother when she is a minor may refuse the marriage when she becomes of majority age.
An aylonit is a woman who never reaches puberty. Categorically she cannot have children (a woman who can have children cannot be called an aylonit). In both of these cases the marriage is annulled.
1) [A minor] who refused her husband, a secondary incest prohibition, or an aylonit is not entitled to a ketubah or to the usufruct [of her dowry] or to maintenance, or to the worn-out articles [of her dowry].
a) If from the outset he had married on the understanding that she is an aylonit she is entitled to a ketubah.
2) A widow who was married to a high priest, a divorced woman or a halutzah who was married to a regular priest, a mamzereth or a netinah who was married to an Israelite, or the daughter of an Israelite who was married to a Natin or a mamzer is entitled to a ketubah.
Section one: The rule in all of these cases is that the woman does not receive a ketubah, nor is the husband liable to pay for her maintenance, nor does she receive the usufruct from her dowry which he used while they were married, nor does she receive compensation for things that she brought into her marriage which her husband has used up. In other words she gets no financial benefits from her husband that would accrue to her by being married to him, nor does he does have to return to her any benefits that he received during the marriage.
The girl who refused the marriage loses her benefits because by refusing the marriage she is in essence annulling it.
The aylonit loses her benefits because her marriage is considered to be mistaken. That is to say, since the man didnt know that she was an aylonit and had he known he would not have married her, the marriage is annulled. That is why in the next section the mishnah states that had he married her knowing that she was an aylonit, he is obligated to give her a ketubah.
The secondary incest prohibitions (see Yevamot 2:4) do not receive a ketubah because the Sages fine them for not having observed the laws of incest. Below we shall see that these fines exist only for those who transgress rabbinic marital prohibitions but not Biblical ones.
Section two: The prohibitions in this mishnah are called prohibitions of holiness in Yevamot 2:4. Even though all of these marriages were prohibited, the women still receive their Ketubot, and according to the Talmud they also receive all of the other benefits listed in this mishnah.
What is seemingly strange here is that although the prohibitions in this section are from the Torah and those in the previous section of the mishnah are only rabbinic prohibitions, in these latter cases the woman is not fined whereas in the former cases she was. The answer is that the rabbis felt the need to strengthen their own prohibitions with penalties; a woman who marries a man prohibited to her only through rabbinic law does not receive benefits. Hence she will not agree to be married in such a case. In contrast, Biblical prohibitions are sufficiently strong to stand on their own, without additional sanctions. Hence, these women do receive the benefits.