Our Mishnah deals with a case in which one spouse refuses to take part in the obligations of marriage and to live with the other as husband and wife. The Mishnah sets out the law regarding a wife who refuses and a husband who refuses, along with the monetary penalty in each of the two cases.
The wife who rebels against her husband:
A wife who refuses to live with her husband is called a "moredes" - from the word rebellion, since she is unwilling to fulfill her obligations. The Mishnah rules that we reduce her kesubah by "shivah dinarin" - seven dinars each week, her kesubah being two hundred dinars. Rabbi Yehudah disagrees and says: "shivah tarpe'ikin" - seven tarpe'ikin, each tarpe'ik being half a dinar, so that his amount is half the amount of the first Tanna.
Until when do we keep reducing?
Her kesubah is limited to two hundred zuz, so by simple arithmetic there is a limit to the deduction. On this point the Tannaim disagree:
The first Tanna: We reduce until her kesubah is used up, and at that point we stop. The husband gives her a get and she leaves without a kesubah, but we do not continue to obligate her beyond that. Even if other property comes to her while they are still married, such as an inheritance, we do not deduct from it.
Rabbi Yosei: We continue reducing even beyond the value of the kesubah, and the balance is recorded as a debt. So if she inherits property from elsewhere, from her father or her grandfather, the husband will be able to collect that amount when it reaches her hands.
The husband who rebels against his wife:
In the reverse case, a husband who refuses to live with his wife has an amount added to her kesubah, and he becomes obligated to her for more than the two hundred zuz: "shloshah dinarin" - three dinars each week. The addition is not equal to the amount of the reduction, because the Gemara explains that a husband's distress at being denied marital relations is greater than a wife's, and therefore the amount of the reduction is higher than the amount of the addition.
Here too Rabbi Yehudah follows his own approach: just as with the rebellious wife the reduction is seven tarpe'ikin and not seven dinars, so too with the rebellious husband the addition is "shloshah tarpe'ikin" - three tarpe'ikin, half the amount, since each tarpe'ik is half a dinar.
The practical halachah:
The Gemara concludes that the halachah does not follow our Mishnah, but rather the later enactment of the Sages: we announce concerning her for four consecutive weeks that this woman is rebelling against her husband, and we send her messengers from the beis din who tell her: even if your kesubah is one hundred maneh - an enormous sum - you have forfeited all of it. And we inform her both before the announcement and after the announcement. If she persists in her rebellion, she leaves without any kesubah at all.
In summary: We learned the law of the rebellious wife - a reduction of seven dinars a week (and according to Rabbi Yehudah, seven tarpe'ikin), and the dispute between the first Tanna and Rabbi Yosei as to whether we reduce only up to the value of the kesubah or even beyond it, as a debt collected from future property; and the law of the rebellious husband - an addition of three dinars a week (and according to Rabbi Yehudah, three tarpe'ikin), which is not equal to the amount of the reduction because the husband's distress is greater. In practice the halachah does not follow our Mishnah, but rather the enactment of the Sages of four announcements and warnings, at the end of which the rebellious wife leaves without any kesubah at all.