Ketubot, Chapter Five, Mishnah One
As we have learned on several occasions, the minimum ketubah payment is 200 zuz. Our mishnah talks about one who wants to add on to that amount or one who wants to subtract from the amount.
1) Although [the Sages] have said: a virgin collects two hundred and a widow one maneh, if he wishes to add, even a hundred maneh, he may do so.
2) If she was widowed or divorced, either after betrothal or after marriage, she is entitled to collect the entire amount.
a) Rabbi Elazar ben Azaryah says: [a woman widowed or divorced] after marriage receives the entire amount;
1) After betrothal [but before marriage], a virgin collects two hundred zuz and a widow only one maneh, for the man wrote her [the additional amount] in order to marry her.
3) Rabbi Judah says: if he wishes he may write for a virgin a document for two hundred zuz and she writes I have received from you a maneh, or for a widow [he may write a document for] a maneh and she writes, I have received from you fifty zuz.
a) Rabbi Meir says: Any man who gives a virgin less than two hundred zuz or a widow less than a maneh is engaging in licentious sex.
Section one: A husband may increase his wifes ketubah by whatever amount he so desires. Clearly wives from rich families would have demanded higher guarantees. Without this mishnah one might have thought that the rabbis set an amount that was meant to be equal for all women. This would have prevented a wife from a poor family from being embarrassed that her ketubah is less than that of a wife from a rich family. The mishnah teaches that a husband is allowed to increase the amount and that we are not concerned lest poor folk are embarrassed.
Section two: Both the first opinion in this section, and Rabbi Elazar ben Azaryah agree that if the wife is divorced or widowed after having been betrothed but before having been married, she collects the basic payment of 200/100. However, there is a disagreement with regard to the extra amount. According to the first opinion, she collects that amount as well. Rabbi Elazar ben Azaryah says that the extra amount is collected only upon marriage, for the only reason that he wrote the extra amount was in order to marry her. If, for whatever reason, the betrothal is terminated before marriage, she does not receive the extra.
Section three: This section deals with a man who wants to write a ketubah of less than 200/100 for his wife. Note that the wife does not object. Evidently she (or her family) wants this man enough that she is willing to compromise on the amount of the ketubah. Rabbi Judah says that the husband may employ a legal fiction whereby he can reduce the ketubah. First he writes the full ketubah of 200/100, as is normally done. Then she writes him a receipt for 100/50 zuz, even though she never received that amount. This means that when he does pay the ketubah, he will be liable for only 100/50 more zuz. In this way, Rabbi Judah retains a legal fiction whereby the actual ketubah does state the normal amount. Someone looking at her ketubah will not know that he has not abided by the fixed ketubah amount of 200/100. He also allows a husband with lesser means to marry.
Rabbi Meir says that anyone who writes less than 200/100 and then engages in sexual intercourse with his wife is having licentious sex. A financial guarantee that binds the man to the woman is distinguishes marriage from prostitution. Without a large enough guarantee a husband could buy a wife for a night, and divorce her the next day. Indeed other cultures, including Arab culture, had what was called a wife for a night. There is even some reflection of this practice in the Talmud. Rabbi Meir takes a strong stance against this practice.