Siman 18

There is no kiddushin with those forbidden as arayot, and they are those liable for karet and those liable for death by beit din – kiddushin does not take effect with them, as it is written regarding the sister of a wife (Leviticus 18:18) "And a woman to her sister you shall not take," there shall not be for you "taking" (likuhin) with her, and all arayot were compared to one another as it is written (Leviticus 18:29) "For whoever shall do any of these abominations shall be cut off," all arayot were compared to the sister of a wife; just as with the sister of a wife kiddushin does not take effect, so too with all arayot. And the offspring from them is a mamzer, for mamzerut depends on the taking effect of kiddushin as I wrote in siman 4, section 13, except for a niddah; even though she is subject to karet, nevertheless kiddushin takes effect with her, as it is written (Leviticus 15:24) "And her niddah impurity shall be upon him," to say that even during the time of her niddah impurity there is "becoming" (havayah) with her, and "becoming" refers to kiddushin, that she makes herself become his, and likewise the offspring from her is not a mamzer as I wrote there.

But regarding those liable for negative commandments and those liable for positive commandments—kiddushin take effect, and they are complete kiddushin. Even though they committed a transgression and he is obligated to divorce her, nevertheless, his kiddushin are kiddushin and the children are not mamzerim, as it is written (Deuteronomy 21:15): "If a man has two wives, one beloved and one hated." Is there one who is hated before the Omnipresent? Rather, she is hated in her marriage, for she is of those liable for negative or positive commandments, and the Merciful One said "If there be"—implying that there is "havayah" [ibid. 68a]. And even those liable for negative commandments of the priesthood, such as a widow to a Kohen Gadol, or a divorcee or a chalalah to an ordinary Kohen, for whom the Torah increased additional mitzvot for Kohanim, nevertheless kiddushin take effect, as it is written (Leviticus 21:15): "And he shall not profane his seed" [Temurah 5b]—he creates profanation (chalal status) but he does not create mamzerim. And since the offspring is not a mamzer, it follows automatically that kiddushin take effect with her, for one is dependent on the other as we have written. Therefore, we do not say regarding those liable for negative commandments that the kiddushin should not be effective based on the principle "anything the Merciful One said 'do not do,' if one did it, it is not effective," since the Torah explicitly included them [ibid.]. Except for a yevamah to a stranger, for even though she is of those liable for negative commandments, kiddushin do not take effect with her due to doubt, as we have written in siman 159; see there. Likewise, with a gentile woman or a maidservant, kiddushin do not take effect with them as they are not subject to kiddushin, and the offspring also follow them as we have written in siman 4, and they are not mamzerim; see there. And certainly regarding rabbinic prohibitions, such as secondary relations (shniyot) to the arayot or a chalutzah to a Kohen, kiddushin take effect with them. And all the more so regarding one who marries a woman in addition to his wife; even though he violated the enactment of Rabbeinu Gershom, nevertheless the kiddushin take effect. And know that in any place where kiddushin do not take effect, she does not require a get if he betrothed her, except for a married woman who married by mistake where they thought the husband died and afterwards the husband arrived, for she requires a get for the reason explained at the end of siman 17; see there.

And one must ask a question regarding this: behold, "anyone who betrothes, betrothes according to the will of the sages," as Chazal said in several places, and the sages certainly would not be pleased that he should betroth through a prohibition, and thus the kiddushin should be voided? And the answer to this is that this reasoning cannot be said unless the kiddushin were entirely valid according to the will of the sages, but afterwards there is a reason to void them due to some grounds, such as the claim of duress regarding gittin at the beginning of Ketubot, or so that his cancellation of a get not in the presence of the messenger shall not be effective [Gittin 33a], or regarding the get of a dangerously ill person so that he shall not be able to retract it [ibid. 73a], or if they even need to void the kiddushin immediately at the time of the kiddushin due to some grounds, such as where he betrothed her against her will [Bava Batra 48b], or such as a minor orphan who was betrothed and did not have relations after reaching majority and another came and betrothed her [Yevamot 110a], where in the essence of the kiddushin there is no concern and they void them for another reason—in this, they rightly said "anyone who betrothes, betrothes according to the will of the sages" and the sages voided the kiddushin. But this one who betrothed from the outset through a Torah prohibition or a rabbinic prohibition and entered into the kiddushin from the outset not according to the will of the sages, how can we say that he betrothed according to the will of the sages? And even though he said "according to the law of Moses and Israel"—certainly it is so that according to the law of Moses the kiddushin take effect in cases of those liable for negative commandments [and see Tosafot Bava Metzia 70b s.v. tashikh, and in the Taz Yoreh Deah at the beginning of siman 117] [and so it appears in the Mordechai at the beginning of the third chapter of Kiddushin, see there].