פירוש על יבמות 4:13

כל שאר בשר שהוא בלא יבא – every nearness which is [a violation of] a negative commandment and even if there is no extirpation [attached to it].

Introduction The first section of this mishnah defines a mamzer. The second section teaches that the prohibition of a wife’s sister (Leviticus 18:18) is only while the wife is still alive, but is effective even if the couple is divorced. However, once the wife dies he may marry her sister.

כל חייבי כרת – but not those who are liable [for violating] a negative commandment, and such is the Halakha. For all that whose prohibition is a prohibition of extirpation, the offspring is illegitimate/Mamzer, except from that of a menstruant woman, but with those who violate negative commandments, the offspring are not Mamzerim/illegitimate.

Who is a mamzer? [The offspring of a union with] any relative with whom cohabitation is forbidden, the words of Rabbi Akiva. Shimon the Yemenite says: [The offspring of any union] for which one is obligated kareth at the hands of heaven; and the halachah is like his words. Rabbi Joshua says: [The offspring of any union] for which one is obligated death at the hands of a court.
Rabbi Shimon ben Azzai said: I found a scroll of genealogical records in Jerusalem, and it was written on it, “So-and-so is a mamzer [having been born] from an adulterous woman”, which confirms the view of Rabbi Joshua. In this section there are three opinions as to which type of forbidden unions create mamzers. Rabbi Akiva’s opinion is the strictest: any forbidden union of an incestuous nature creates a mamzer. This would preclude only forbidden unions that are not incestuous, such as a kohen and a divorcee. Shimon the Yemenite (who is not called rabbi) holds that any forbidden union punishable by kareth creates a mamzer. Shimon the Yemenite rejects Rabbi Akiva and holds that forbidden unions that are merely prohibited but not punishable by kareth or death do not create mamzers. An example of such a case is a shomeret yavam who gets remarried to an outsider without first having yibbum or halitzah with her yavam. According to Rabbi Akiva the child of such a marriage is a mamzer and according to Shimon the Yemenite the child is not. Interestingly, the mishnah explicitly states that the halakhah is according to this view. This is one of the few times that the Mishnah makes such a remark. Rabbi Joshua is even more lenient concerning the creation of mamzers. Only a union punishable by death creates mamzers. Rabbi Shimon ben Azzai claims that he found a scroll of genealogical records in which it was recorded that So-and-so was a mamzer because he was the son of an adulterous affair, which is punishable by death. From here he concludes that the halakhah is like Rabbi Joshua. However, Rabbi Akiva and Shimon the Yemenite could both claim that just because this mamzer was from an adulterous affair punishable by death does not prove that the halakhah is like Rabbi Joshua.

If a man’s wife died, he is permitted to marry her sister. If he divorced her and then she died he is permitted to marry her sister. If she was married to another man and died, he is permitted to marry her sister. If a man’s sister-in-law died, he may marry her sister. If he performed for her halitzah and then she died, he is permitted to marry her sister. This section teaches that the sister of one’s wife is only forbidden during the wife’s lifetime, even after divorce. This is stated explicitly in Leviticus 18:18, “Do not marry a woman as a rival to her sister and uncover her nakedness in the other’s lifetime.” Once the wife dies, whether while the couple is still married, after they are divorced or after her remarriage, the husband may marry her sister. However, if any of these things occur and the wife is still alive, he may not marry her sister. Similarly, a man cannot marry the sister of his yavamah while she is alive, even after he performed halitzah for her. However, after she dies he may marry her sister.