then sometimes, where he was not detained unavoidably but he fulfilled the condition willingly to effect the divorce, and the wife thinks that he was detained unavoidably, she will sit deserted, forever unable to remarry. And the concern due to licentious women is, as, if you said: Let it not be a bill of divorce, then sometimes, when he was detained unavoidably and she thinks that he was not detained unavoidably, she goes and remarries. And the result will be that the bill of divorce is void, and her children from the second marriage will be mamzerim, products of an adulterous relationship.
ומי איכא מידי דמדאורייתא לא להוי גט, ומשום צנועות ומשום פרוצות שרינן אשת איש לעלמא?!
The Talmud questions the following premise: By Torah law, a condition that is unfulfilled due to circumstances beyond one’s control is considered fulfilled, and it is merely by rabbinic ordinance that it is deemed unfulfilled: And is there a matter where by Torah law it is not a bill of divorce, but due to virtuous women and due to licentious women we permit a married woman to others?
אין, כל דמקדש אדעתא דרבנן מקדש, ואפקעינהו רבנן לקידושי מיניה.
The Talmud answers: Yes, it is within the authority of the rabbis to institute an ordinance freeing the woman from the marriage, as anyone who betroths a woman, betroths her contingent upon the agreement of the rabbis, and in certain cases, such as those mentioned above, the rabbis invalidated his betrothal retroactively.
אמר ליה רבינא לרב אשי: תינח קדיש בכספא. קדיש בביאה מאי איכא למימר? שויוה רבנן לבעילתו בעילת זנות.
Ravina said to Rav Ashi: That works out well if he betrothed her with money, as in that case, the courts could declare the money ownerless, and one cannot betroth a woman with money that is not his. However, if he betrothed her with sex, what can be said? Rav Ashi answered: The rabbis rendered his sex licentious sex.