QUESTIONS: The Mishnah describes the situations in which a woman does not receive her Kesuvah when she is divorced. The Mishnah says that when a woman transgresses "the law of Moshe and the law of Yehudis (the Jewish woman)" she is divorced without a Kesuvah. The Mishnah gives examples of transgressions that fall into each of those two categories, "the law of Moshe" and "the law of Yehudis." A woman who feeds her husband fruit from which Ma'aser has not been separated transgresses "the law of Moshe" and is divorced without a Kesuvah. "The law of Yehudis" ("Das Yehudis") includes a woman who exits her home with her hair uncovered.
(a) If a man does not mind that his wife goes out with her hair uncovered, is he permitted to remain married to her?
(b) If he is permitted to remain married to her and chooses not to divorce her, does she still lose her Kesuvah (upon his death, or if he decides to divorce her for another reason)?
(a) This question is the subject of discussion in the Gemara in Sotah (25a), where the Gemara asks whether a man may choose to remain married to his wife who sins. It is not clear from the Gemara whether the question is resolved. The RA'AVAD (cited by the Rosh, Rashba, and Ran) writes that the question remains unanswered, and out of doubt the man is not forced to divorce his wife. The RASHBA, RITVA, and others maintain that the Gemara itself concludes that the man is not forced to divorce his wife.
The Rishonim agree that in practice Beis Din does not force a man to divorce his wayward wife, but it nevertheless is a Mitzvah for him to do so. The source for this Mitzvah, as the MORDECHAI writes, is the Gemara in Gitin (90a-b) that says that if a man sees that his wife transgresses the law of Yehudis such as by going out with her hair uncovered he should divorce her, and if he remains married to her he is acting with "Midas Adam Ra," in the way of an evil person. (It seems that the same applies to a wife who causes her husband to sin such as by feeding to him untithed food.)
Similarly, the RAMBAM (Hilchos Ishus 24:16) rules that Beis Din does not force the husband to divorce his wife, but nevertheless he fulfills a Mitzvah if he does so (Hilchos Gerushin 10:22). (The CHELKAS MECHOKEK EH 115:18, however, writes that the wording of the Rambam in Hilchos Ishus implies that there is not even a Mitzvah for the husband to do so, and that the Rambam in Hilchos Gerushin might be referring to a woman who acts in an exceedingly licentious manner.)
(b) The question whether or not she loses her Kesuvah if her husband chooses to stay married to her depends on the reason why she loses the Kesuvah in the first place.
1. The ROSH writes that a man may divorce his sinful wife without a Kesuvah only when her transgressions affect him, such as in the cases mentioned in the Mishnah. If she sins just between herself and Hash-m, she remains entitled to receive her Kesuvah. The reason for this is that her loss of the Kesuvah when she sins against her husband is not a punishment for sinning. Rather, she loses her Kesuvah because there is no obligation for a man to give his wife a Kesuvah when she is the cause of the divorce. When she causes him to sin it is impossible for him to live with her, and thus she is the cause of the divorce and loses her entitlement to the Kesuvah.
Consequently, if he chooses to remain married to her, when he dies or divorces her for a different reason she should be entitled to receive her Kesuvah, since her sins did not cause him to divorce her.
Another consequence of this logic exists in a case in which the husband also willfully transgresses the sins mentioned in the Mishnah. In such a case, his wife does not lose her Kesuvah upon divorce. Since it is clear that he is not divorcing her because she causes him to sin but because of some other reason, he must give her the Kesuvah (MORDECHAI quoted by HAGAHOS ASHIRI 6:9).
The RAMBAM in a Teshuvah (#193) discusses a case in which a woman refuses to immerse in a Mikvah and her husband knows about it and remains silent. The Rambam rules that if the husband divorces her, he is exempt from giving her the Kesuvah so that she not gain by sinning -- "she'Lo Yehei Chotei Niskar." It is not clear why this principle should prevent her from receiving her Kesuvah. She would not receive her Kesuvah because she sinned but because every woman receives a Kesuvah upon divorce! Perhaps the Rambam refers to a case in which the husband divorces his wife at the insistence of the Chachamim (as the Rambam writes in an earlier Teshuvah, that a man who willfully lives with his wife who is a Nidah is put in Cherem for remaining married to her). Hence, it is indeed her sin that causes her to be divorced, and thus she should not profit by receiving her Kesuvah. (The Mordechai and Rosh cited above might agree that she loses her Kesuvah in such a case.)
2. The RAMBAM (Hilchos Ishus 24:16) writes that even when the man chooses to remain married to her, she loses her Kesuvah. If her husband dies or decides to divorce her for a different reason, she still does not receive her Kesuvah.
The Rambam reasons that since the purpose of the Kesuvah is to discourage a husband from impulsively divorcing his wife at whim, in the case of a wife who sins and tries to cause her husband to sin we do not care if her husband divorces her at whim. On the contrary, we would prefer that he divorce her (as mentioned in (a) above).
The RITVA writes that most Rishonim do not accept the reasoning of the Rambam. They rule that a woman does receive her Kesuvah if the husband does not divorce her because of her sin (as the Mordechai rules).
HALACHAH: The SHULCHAN ARUCH (EH 115:4) rules that a man may remain married to his sinful wife if he so desires, but it is a Mitzvah to divorce her.
Regarding whether she loses her Kesuvah if he remains married to her, the Poskim (Chelkas Mechokek loc. cit., and Beis Shmuel EH 115:19) cite the Rambam who says that she does lose her Kesuvah.
Nowadays, however, when we do not have the power to force a man to divorce his wife, RAV MOSHE FEINSTEIN zt'l (Igros Moshe EH I:114) rules that she does not lose her Kesuvah even if he wants to divorce her for not following the Mitzvos. Since it is up to her to accept the divorce willingly, she may demand from her husband any sum that she wants for the divorce, including the sum written in the Kesuvah.
Rav Moshe Feinstein adds that if the husband knew before the marriage that his wife would be lax in her observance of the Mitzvos of Das Yehudis and, despite that knowledge, he still married her, he showed that he accepted that flaw in her and is obligated to give her the Kesuvah, as the Mordechai rules. For this reason, Rav Moshe Feinstein rules that if the husband did not specifically tell his wife before the marriage that he wants her to cover her hair, he cannot assume (based on a Chazakah) that she will cover her hair (because many women today do not cover their hair), and thus it is as if he knew that she might not cover her hair. Hence, she does not lose her Kesuvah.