Halakhah for Yevamot 121:12

Not to have sexual relations with a woman without a marriage contract and betrothal: That we have been prevented from having sexual relations with a woman without a marriage contract and betrothal. And about this is it stated (Deuteronomy 23:18), "No daughter of Israel shall be a prostitute." And Rambam, may his memory be blessed, wrote (Sefer HaMitzvot LaRambam, Mitzvot Lo Taase 355) and this is his language: "The negative commandment about this matter has already been duplicated with a different language in the verse (Leviticus 19:29), 'Do not desecrate your daughter to make her a harlot' - and the [following is the] language of Sifrei Kedoshim 7:3, '"Do not desecrate your daughter" - this is one who gives over his single daughter not for the sake of marriage and also [a woman] who gives herself over not for the sake of marriage.' And hear from me for what [reason] this negative commandment of strong language was duplicated, and for what was it added to (see Mishneh Torah, Virgin Maiden 2:17): That which He already made precede from His laws that one who has sexual relations with a virgin - whether it be a seduction or a rape - is not obligated any one of the punishments, except only to [give] money and to marry the woman with which he had sexual relations, as it is explained in the verse, would let it come into our thoughts that since this thing only requires the payment of money, that this law goes according to the procedure of financial law. And [if so, just] like a person has the right to give whatever of his money to his fellow and he leaves it to him to do his will with that which is [now] his; so too has [the father] the right to take the maiden with him and to give her to a man to have sexual relations with her, since that is his law that is fitting to him - meaning to say the fifty shekel-coins of silver that go the father of the maiden. And this [father] will also give her on condition that he takes from him such and such dinar-coins. And he is prevented from this [thought] and it is told to him, 'Do not desecrate your daughter to make her a harlot.' Since that which is My law with her to only take money, however, is only when there is an incident when a man seduces or rapes [her]; but when the matter is with the consent of both of them together and it is public, there is no permissibility to this at all from any angle. And He showed the explanation for this and stated (Leviticus 19:29), 'lest the land fall into harlotry and the land be filled with depravity.' [This is] since the existence of seduction and rape is limited, but when the matter would be by choice and consent, it would spread and fill the land. And this reason is very nice and it enhances the verse. And similar to this is all that which the Sages have mentioned and all that they agreed upon regarding the Torah laws." To here is his language, may he be blessed. And Ramban, may his memory be blessed, wrangled with him about this (in his critique of Sefer HaMitzvot LaRambam, Mitzvot Lo Taase 355) and said that this negative commandment of the prostitute is not coming to warn one having sexual relations without a wedding contract and betrothal, as the wedding contract is neither a commandment nor a form of acquiring a woman, at all, according to the Torah. But [rather] the main negative commandment [here] is coming to warn not to have sexual relations with a woman that is forbidden [in marriage] to the man having sexual relations in such a way that betrothal would not be effective for him with her. As they, may their memory be blessed, elucidated in the Gemara (Yevamot 61a), that the harlot (zonah) that is mentioned in every place in the Torah is none other than a woman who an Israelite has sexual relations with, when betrothal would not be effective for him with her. And this is the harlotry that the Torah distanced and loathed forever and [here] it warned the [man] and the [woman] about it. And so too from the foundation of this matter is that the verse warns the court that they should not let a woman be abandoned among them, since her end will be to have sexual relations with men that she is forbidden to [in marriage], to the point that betrothal is not effective for them with her. As there is no doubt that a woman abandoned to the many will not be exacting afterwards 'between a piece of permissible fat and a piece of forbidden fat.' And so too does it warn the father of the girl about this explicitly in another verse; that he should not abandon her to harlotry and not to give her over to one who cannot have betrothal with her. And about this is it stated, "Do not desecrate your daughter to make her a harlot." And it is all from the reason mentioned - since she will have sexual relations with one who she is forbidden to [in marriage]; not from the reason of marriage contract and betrothal, as is the opinion of Rambam, may his memory be blessed.