And your mnemonic to remember how this might occur is as follows: Died, was born, entered into levirate marriage, died, was born, entered into levirate marriage. In other words, there were several brothers, and one, Reuven, died, before another, Yissakhar, was born, and another brother, Shimon, entered into levirate marriage with the deceased’s wife, and there was another brother, Levi, who died as well, and yet another brother, Zevulun, was born, and a sixth brother, Yehuda, entered into levirate marriage with the deceased’s wife. In this case, if Shimon and Yehuda were to die childless, their wives would come before the surviving brothers, Yissakhar and Zevulun, for levirate marriage. To one of them, Yissakhar, the wife of the first brother, Reuven, is prohibited, and for the other brother, Zevulun, the wife of the second brother, Levi, is likewise prohibited.
This is an example of the type of case analyzed in the third chapter, in which the ruling is that the woman who is forbidden to this brother is permitted to that one, and she who is forbidden to this one is permitted to that one. In any case, Rabbi Ḥiyya incorporates the opinion of Rabbi Shimon into this principle, as he maintains that this scenario can apply to each case stated in the mishna. If so, the mishna evidently does deal with disputed legal rulings. How, then, can Rabbi Yehuda HaNasi claim that the cases of the mishna are unanimous?

§ Rather, Rabbi Yehuda HaNasi does not hold in accordance with these general statements applied by Rabbi Ḥiyya, and therefore he maintains that no issue subject to dispute was taught in the mishna. Rav Adda Karḥina, who was sitting before Rav Kahana, said in the name of Rava: Actually, one can explain that Rabbi does hold in accordance with these general statements laid out by Rabbi Ḥiyya. And this is what he said to Levi: In the case of his mother who had been raped by his father, you find this case with only one of the women; however, you cannot find it with two. In other words, the terms mentioned by Rabbi Ḥiyya above: She who is forbidden to this one is permitted to that one, and: A sister who is a sister-in-law performs either ḥalitza or levirate marriage, apply only partly to this complex case.

The Gemara elaborates: If Ya’akov, the father, raped two sisters who gave birth to two sons, and he had two other sons who married these raped sisters and died, in this scenario you find a case of her sister who is her sister-in-law, as there is a yevama who comes before one of the brothers who is a forbidden relative and also a sister and a sister-in-law of another yevama. However, you cannot find the principle of: She who is forbidden to this one is permitted to that one. Although it is possible that one’s brother’s wife who is one’s mother might come before one for levirate marriage, just as he is forbidden to his mother, he is likewise forbidden to his mother’s sister.

And if the father raped two unrelated women, who gave birth to two sons and then married two other sons of the same father who subsequently died, you find the case of: She who is forbidden to this one is permitted to that one, as each of the two raped women comes before one of the brothers for levirate marriage while she is forbidden to the other as his mother. However, you do not find a situation of: Her sister who is her sister-in-law. Therefore, the case of one’s mother who was raped by one’s father cannot be included in the list of the mishna, as the characteristics stated by Rabbi Ḥiyya do not apply to this case.

§ Rav Ashi stated a different explanation: Actually, Rabbi Yehuda HaNasi does not hold in accordance with these general statements of Rabbi Ḥiyya, and the mishna does deal with halakhot that are in dispute. According to his opinion, what is the meaning of the phrase: It seems to me that he has no brain in his head, that Rabbi Yehuda HaNasi said to Levi?

According to Rav Ashi, this is what Rabbi Yehuda HaNasi said to Levi: What is the reason that you were not precise in your interpretation of the mishna? As the mishna is in accordance with the opinion of Rabbi Yehuda, who prohibited the case of a woman who was raped by one’s father. Accordingly, the rulings of the mishna cannot be attributed to any opinion that is not in line with that of Rabbi Yehuda. What is the proof that this mishna is indeed in accordance with the opinion of Rabbi Yehuda?

As it teaches in the next mishna: Six women with whom relations are forbidden are more severe than these enumerated in the previous mishna, because they may marry only others and can never be married to any of the brothers, and therefore their rival wives are permitted. These women include: His mother, his father’s wife, and his father’s sister. Rav Ashi infers: What is the meaning of: His mother? If we say that this mother is married to his father, then this is the same case as: His father’s wife, which would mean that the mishna lists only five cases, not six.

Rather, is it not referring to a woman raped by his father? And it is taught in the mishna that the halakhot of levirate marriage do not apply to them because they may marry only others, which indicates: Others, yes; the brothers, no. Since each of the brothers are sons of the same father, each one is prohibited from marrying the mother of one of the other brothers, as although she is not his mother, she is nevertheless a woman raped by his father, whom one may not marry. Who did you hear who holds in accordance with this conclusion that a woman raped by one’s father is prohibited to all his sons? It is Rabbi Yehuda who prohibits a woman raped by his father. Due to that reason the case of a woman raped by one’s father was not taught in the first mishna.

Ravina said to Rav Ashi: Even according to the opinion of Rabbi Yehuda you can find this possibility that a woman raped by a father comes before the son for levirate marriage. What if one of the brothers transgressed and married a woman raped by his father? Even Rabbi Yehuda concedes that this is a violation of a regular prohibition that does not incur karet, and therefore the marriage is valid. Consequently, if this brother died childless, this woman would come before her son for levirate marriage. The Gemara rejects this proof: The tanna does not teach cases of what if, i.e., the mishna does not cite an example that could result only from a transgression.

Rav Ashi said to Rav Kahana: Even without a hypothetical: What if, you can find an example of a woman raped by a father who is not forbidden to the son in marriage. How so? Ya’akov, the father, raped his daughter-in-law, from whom he fathered a son. And the son, Reuven, the husband of the daughter-in-law, died childless. And as Ya’akov had two sons, the deceased Reuven and a son by Reuven’s wife whom Ya’akov had raped, Reuven’s wife would then come before her son for levirate marriage. And since she is forbidden, her rival wife is also forbidden. Consequently, a case of this kind is possible without the levirate marriage resulting from an illicit marriage.

Rav Kahana said to Rav Ashi: The mishna deals with cases of legitimate brothers, whereas it does not deal with cases of illegitimate brothers. The offspring of a man who rapes his daughter-in-law is a mamzer, and cases of this kind are not discussed in the mishna. The Gemara comments: Nevertheless, despite Rabbi Yehuda HaNasi’s criticism, Levi established this additional possibility of a woman raped by one’s father in his mishnayot.

As Levi taught in his baraita: With regard to the case of his mother, at times she exempts her rival wife, and at other times she does not exempt her rival wife. How so? If his mother was married to his father and after his father’s death she illicitly married her son’s paternal brother, who then died, this is a case of: His mother who does not exempt her rival wife. The reason is that her marriage to his brother does not take effect at all, as it was forbidden on pain of karet. Since this marriage never occurred, only the other wife, the so-called rival wife, is considered a wife of the brother, and she may enter into levirate marriage.