The Gemara asks: Is this relationship not forbidden by Torah law? As it is written: “You shall not uncover the nakedness of your daughter-in-law” (Leviticus 18:15). The Gemara emends: Say instead his son’s daughter-in-law. The Gemara asks: And does the prohibition against having a relationship with his son’s daughter-in-law indeed have a conclusion? Isn’t it taught in a baraita: His daughter-in-law is a forbidden relation by Torah law, his son’s daughter-in-law is a secondary forbidden relation, and similarly, you say the daughter-in-law of his son and the daughter-in-law of his son’s son until the end of all generations are secondary forbidden relationships. Rather, say instead that Rav was referring to his daughter’s daughter-in-law.

As Rav Ḥisda said: I heard this matter from a great man, and who was that great man? It was Rabbi Ami, and he said: They prohibited a daughter-in-law only due to the daughter-in-law. Rav Ḥisda heard this in his youth but did not understand the meaning. The Chaldean astrologers said to me: You will be a teacher.

Rav Ḥisda further said: I said to myself: If the astrologers meant that I will become a great man and one who teaches the public, I will certainly be able to reason and understand this matter with my knowledge. If the astrologers meant that I will become the teacher of children, I will ask it of the Sages who come to the synagogue and in that way I will learn the meaning of Rabbi Ami’s teaching. Now I understand the matter on my own. Rabbi Ami meant: They prohibited his daughter’s daughter-in-law only due to his son’s daughter-in-law, to avoid confusion between these daughters-in-law. The rabbinic decree prohibited one’s daughter’s daughter-in-law but did not extend to subsequent generations.

Various Sages proceed to give contemporary examples of families where the halakhic status of the daughters-in-law of the sons and the daughters-in-law of the daughters could be confused with each other. Abaye said to Rava: I will explain to you with an example how one might become confused about these daughters-in-law. For example, this would be possible in the case of the daughter-in-law of the house of bar Tzitai, as there the children of the sons and the daughters of the same family lived together, and it was possible to confuse the halakhic status of the sons’ daughters-in-law and the daughters’ daughters-in-law. Rav Pappa said: For example, the daughter-in-law of the house of Rav Pappa bar Abba. Rav Ashi said: For example, the daughter-in-law of the house of Mari bar Isak.

§ A dilemma was raised before the Sages: What is the halakha with regard to the wife of one’s mother’s maternal half brother? The Gemara presents the different sides of the question: Both the wife of one’s father’s maternal half brother and the wife of one’s mother’s paternal half brother contain some aspect of a father, and perhaps this is the reason that the Sages enacted a prohibition. That is, they were both forbidden rabbinically to avoid confusion with the case of the wife of one’s father’s paternal half brother, who is forbidden by Torah law. But in the case of the wife of one’s mother’s maternal half brother, where there is no aspect of a father whatsoever, perhaps the Sages did not make a decree? Or perhaps this case is no different?

Rav Safra said: She herself, the wife of the mother’s paternal half brother, is forbidden by rabbinic decree, and will we then proceed to issue a decree to prevent violation of a decree? Rava said: Is that to say that all of these rabbinic decrees with regard to secondary relations are not decrees to prevent violation of a decree? For example, his mother is a forbidden relation by Torah law, and the Sages decreed that his mother’s mother is a secondary forbidden relationship. And they decreed that his father’s mother is also a secondary forbidden relationship due to his mother’s mother. And what is the reason? They are all called the house of the grandmother, and therefore people may confuse their halakhic status.

Rava continues: Similarly, his father’s wife is a forbidden relation by Torah law, and the Sages decreed that his father’s father’s wife is a secondary forbidden relationship. And they decreed that his mother’s father’s wife is also a secondary forbidden relationship due to his father’s father’s wife. And what is the reason? They are all called the house of the grandfather.

Also, the wife of his father’s paternal half brother, his uncle, who is mentioned explicitly in the Torah (Leviticus 18:16), is a forbidden relation by Torah law, and the Sages decreed that the wife of his father’s maternal half brother is a secondary forbidden relationship. And they decreed that the wife of his mother’s paternal half brother is also a secondary forbidden relationship due to the wife of his father’s maternal half brother. And what is the reason? It is because they are all called the house of the uncle; it seems that in the realm of forbidden relations the Sages did issue decrees to prevent violation of a decree, and Rav Safra’s claim is incorrect.

If so, then what is the halakha in this case of the wife of his mother’s maternal half brother? Come and hear: As when Rav Yehuda bar Sheila came from Eretz Yisrael to Babylonia, he said: In the West, Eretz Yisrael, they say this principle: For every female relative who is a forbidden relation by Torah law, the Sages decreed on the wife of the equivalent male relative due to her similarity to a secondary forbidden relationship.

And Rava said: Is this really an established principle? Isn’t his mother-in-law a forbidden relation by Torah law, while his father-in-law’s wife is permitted? Also, his mother-in-law’s daughter is a forbidden relation by Torah law, as she is his wife’s sister, yet his mother-in-law’s son’s wife is permitted. His father-in-law’s daughter is a forbidden relation by Torah law, yet the wife of his father-in-law’s son is permitted. His stepdaughter is a forbidden relation by Torah law, yet his stepson’s wife is permitted. His stepdaughter’s daughter, i.e., his wife’s granddaughter, is a forbidden relation, yet the wife of his stepson’s son is permitted.

The Gemara continues: If so, what did that statement of Rav Yehuda bar Sheila come to include? Since his principle is not true in every case, it must be intended to include a specific halakha. Does it not come to include the case of the wife of one’s mother’s maternal half brother, since for every female relative who is a forbidden relation by Torah law, such as his mother’s maternal half sister, the Sages decreed on the wife of the equivalent male relative, in this case his mother’s maternal half brother’s wife, due to her similarity to a secondary relation.

The Gemara asks: What is different with regard to these cases, the wife of his father-in-law or the wife of his mother-in-law’s son, who are permitted, and this case of the wife of a mother’s maternal half brother, who is prohibited? The Gemara answers: This, the wife of a mother’s maternal half brother, is related by a single act of betrothal. One’s mother’s brother is a blood relative, and his wife is therefore a secondary relation. In contrast, these other cases with regard to which the Sages did not issue a decree are related only when there are two acts of betrothal. For example, one’s father-in-law is related to one through one’s marriage to his own wife, and his father in law’s wife is related to him through his father-in-law’s marriage.

§ Rav Mesharshiyya from Tusneya sent a message to Rav Pappi: Let our Master teach us: What is the halakha with regard to the wife of a father’s father’s brother and the sister of a father’s father? Did the Sages prohibit these as secondary forbidden relations? The Gemara presents the different sides of the dilemma: Since one generation below is a forbidden relation, i.e., a father’s sister and the wife of a father’s paternal brother, who are both forbidden by Torah law, perhaps the Sages also decreed about the women one generation above. Or, perhaps the generations are separate and the women in the generation above are not considered to be forbidden relatives.

The Gemara attempts to answer: Come and hear from that baraita cited above, which taught: What are the secondary forbidden relationships that were prohibited? And these women, i.e., the wife of one’s father’s father’s brother and the sister of his father’s father were not reckoned among them. This implies that these women are permitted.

The Gemara replies that this is not conclusive. Perhaps the tanna of the baraita taught some examples and omitted other examples of secondary forbidden relations; i.e., perhaps the list is not exhaustive. The Gemara asks: What else did he omit that he omitted this? It cannot be that the tanna had an exhaustive list except for one case. He either left out more than one case or he included all possible cases. The Gemara answers: He omitted the list of secondary forbidden relationships that were enumerated by the school of Rabbi Ḥiyya, which is listed later. Therefore, this baraita is not conclusive, as the tanna left out many cases.

The Gemara states that Ameimar permitted the wife of one’s father’s father’s brother and the sister of one’s father’s father. Rav Hillel said to Rav Ashi, challenging Ameimar’s statement: I myself saw a list of secondary forbidden relationships written by Mar, son of Rabbana, and it was written there that sixteen women were forbidden. What, is it not that these sixteen must be the eight cases listed in the baraita, and six from the school of Rabbi Ḥiyya, and these two cases of the wife of one’s father’s father’s brother and one’s father’s father’s sister, and this totals sixteen?

Rav Ashi defended Ameimar’s opinion: And according to your reasoning, Rav Hillel, that these cases should be included, there are seventeen cases, as there is the additional case of the wife of a mother’s maternal half brother, whose status was resolved earlier, concluding that she is forbidden. If it is as you say, then there should be seventeen cases. The Gemara answers on behalf of Rav Hillel: This is not difficult.