Kesubos, Chapter 11, Mishnah 6. Our Mishnah lists several irregular marriages, together with the laws governing the kesubah and the additional sum written into the kesubah, and how they are affected by these marriages.
Three marriages in which there is no kesubah:
Hamema'enes - a girl whose father is not available, and who was married off by her mother and brothers under a rabbinic arrangement. She has the right to refuse the marriage and to declare that she does not want it, and she leaves without needing a get.
Shniyah - a relative forbidden by rabbinic law: relatives who are not forbidden by the Torah, but who fall within the general framework of forbidden relatives and are prohibited by the words of the Sages.
Ailonis - a woman who is incapable of bearing children, because she lacks the essential biological features that would have enabled her to have children.
In all three of these cases the Mishnah rules that there is no kesubah, and each for a different reason:
Hamema'enes - she is not divorced by her husband; rather, she leaves on her own initiative.
The shniyah - this is a fine and a punishment imposed upon her by the Sages.
The ailonis - this is a mistaken transaction: the marriage was entered into on false premises, since the husband assumed that she was capable of having children, and in fact this is not so.
The Gemara points out that this affects only the basic kesubah - a maneh for a widow and two hundred for a virgin. But the additional sum, whatever the husband added of his own accord, whose status is that of a gift, is not forfeited.
The conditions of the kesubah:
The Mishnah goes on to list the conditions of the kesubah, those additional provisions that accompany the kesubah, which are likewise affected:
"velo peiros" - the husband need not repay her for the produce he consumed from her property. And some say even more than this: even if the produce is still in his possession and he has not consumed it, he need not return it. This is so even though the marriage has been annulled, and it is possible that it was never valid even retroactively, and nevertheless he is permitted to keep the produce for himself.
"velo mezonos" - he is not obligated to support her.
"velo velaos" - he is not responsible to pay for wear and tear: if her property wore out while he was using it, he is not liable to pay for that.
Regarding support, we must understand what the Mishnah means in the case of the girl who refuses, for as long as they were married the husband was obligated to support her. The Gemara therefore explains that the case is one where the husband traveled abroad, and she borrowed money in order to support herself, and afterwards she refused the marriage - in such a case he need not repay the loan. But with the shniyah and the ailonis the reference is to the period of the marriage itself, that he is not obligated to pay for her support.
The law of wear and tear is likewise not identical in the three cases:
With the girl who refuses: he need not repay for wear and tear, neither of nichsei melog nor of nichsei tzon barzel.
With the shniyah: he need not repay for wear and tear of nichsei melog, but for nichsei tzon barzel he is liable.
With the ailonis: he need not repay for nichsei tzon barzel that wore out, but for nichsei melog he is liable.
However, whatever remains of this property intact, she takes back.
And with the ailonis the Mishnah adds a qualification: if a man marries a woman knowing that she is an ailonis, so that there is no mistaken transaction here and no false claim - "yeish lah kesubah" - she has a kesubah, and of course produce, support and wear and tear as well, for her status is that of an ordinary wife.
Marriages forbidden by the Torah:
From here the Mishnah turns to cases in which the marriage is not legitimate by Torah law:
"almanah leKohen Gadol" - a widow who married a Kohen Gadol.
"gerushah vachalutzah leKohen hedyot" - it is worth noting that the prohibition of a chalutzah to an ordinary kohen is rabbinic, and so either it is included here in any case, or it does not properly belong on this list, and at times it is mentioned there incidentally along with the divorcee.
"mamzeres unesinah leYisrael" - a mamzeres or a nesinah who married a Jew who is forbidden to her by the Torah.
"bas Yisrael lemamzer venasin" - the reverse: a Jewish woman who married a mamzer or a nasin.
In all these cases, surprisingly enough, she does have a kesubah. They receive a kesubah, and they have produce, support and wear and tear.
The reason for this: since these prohibitions are forbidden by the Torah, the Sages held that matters whose character is biblical do not require reinforcement by means of an enactment that denies the kesubah. The cases listed at the beginning of the Mishnah, on the other hand, whose prohibition stems from the words of the Sages, do require reinforcement, and therefore the Sages instituted these penalties, which result in there being no kesubah and no conditions of the kesubah.