Resources for Kesubos 89
1. The גמרא says that if a woman has a כתובה and not a גט and the husband says he lost his שובר then the husband does not have to pay. The גמרא asks that according to רב he should have to pay for the תוספת כתובה. The גמרא answers that he has a מיגו that he could have said I never divorced her so he is believed to say he divorced her but paid the כתובה. תוספות in ד"ה יכול asks that this shouldn’t be a good מיגו since if he never divorced her he would still need to pay her for שאר וכסות. He answers that since she didn’t ask for שאר וכסות it would be like טענו חיטים והודה לו בשעורים where you don’t even get the שעורים. The או"ש in חידושי ר׳ מאיר שמחה in בב"מ סד י"ז ע"ב says a different תירוץ which is a real חריפות. He says that if the woman said that she was divorced then that is considered שויא אנפשה חתיכה דאיסורא and she would be אסורה to her husband. If she cant be with her husband because of what she did then she is a מורדת in which case the husband doesn’t owe her מזונות anyway!
As to תוספות’s answer that it is considered טענו חיטים והודה לו בשעורים, the ריטב"א says you can disagree with תוספות since טענו חיטים והודה לו בשעורים refers to totally different מינים. In our case, money is money so if she said he owes כתובה and he says he owes מזונות then that’s חיטים וחיטים. It should be similar to a case of טוענו מנה של מלוה והודה לו במנה של פּקדון which you are חייב to pay what you admitted to since its all money. Rather, the ריטב"א says his מיגו is that he could have said two things: that he never divorced her and she also said איני ניזונית ואיני עושה. The קהילת יעקב in ב"ק סימן כ"ז אות ד answers the ריטב"א’s question on תוספות from טוענו מנה של מלוה והודה לו במנה של פּקדון as follows: there is a major difference between claiming a loan and claiming מזונות. A loan is a חיוב that you already undertook. Many מפרשים understand the חיוב מזונות is a new חיוב that occurs every day. Every day that your wife is hungry anew the חיוב comes anew. Therefore, they are completely different claims and it would be similar to טענו חיטים והודה לו בשעורים.
There is a מחלוקת as to how ענו חיטים והודה לו בשעורים works. רש"י in ב"ק דף ל"ה ע"ב says that it works because of מחילה, meaning if you didn’t ask for שעורים you must be מוחל it. The רא"ש says that it is a הודאה (which may be the same). With this in mind, the מצפּה איתן points out that there is a ירושלמי that says that if you divorce a woman but don’t pay her כתובה then a חיוב מזונות continues to exist. According to that, תוספות would not be correct לכאורה since if the lady claims she is divorced she is not being מודה that she doesn’t get מזונות since she is still entitled to מזונות if she didn’t get her כתובה!