The Gemara raises a challenge: And say that the verse: “The daughter of your father’s wife” comes to exclude women who were forbidden, as they are liable for violating prohibitions but were nevertheless married to his father, such as a mamzeret. If so, his sister from such a union would not be considered his sister. Rav Pappa said: Betrothal comes into effect with women who are forbidden, and one would be liable for violating prohibitions despite the fact that union with them is forbidden, and so she is called the wife of your father.

This is derived from the verse in which it is written: “If a man has two wives, the one beloved, and the other hated” (Deuteronomy 21:15). Is there one who is loved by the Omnipresent and one who is hated by the Omnipresent? Rather, “beloved” means her marriage is beloved, as it was permitted for her to be married, in accordance with halakha, and “hated” means her marriage is hated because it was not permitted for her to be married, according to halakha. And the Merciful One states: “If a man has two wives,” meaning that both are considered to be married.

The Gemara asks: Say that this verse comes to exclude a union between one’s father and a woman that is forbidden to him as they are liable to receive karet, and that since betrothal does not come into effect with her there is no marriage bond. Perhaps a sister born of such a woman would not be prohibited as the daughter of one’s father’s wife. Rava said that the verse states: “The nakedness of your sister, the daughter of your father, or the daughter of your mother, whether born at home or born outside” (Leviticus 18:9). This includes all daughters, whether from a woman for whom the Sages tell your father: Maintain her within your home, or whether the Sages tell your father she is a woman who is forbidden to him and therefore: Send her out of your home. And the Merciful One states that nevertheless: “She is your sister.” Even the daughter of a woman who was forbidden to your father such that both parties are liable to receive karet is called your sister.

The Gemara asks: Say that whether the Sages say to your father: Maintain her, or whether they say to your father: Send her out, and the Merciful One states that “she is your sister,” this comes to include the additional cases of his sister from a Canaanite maidservant or a gentile woman. The Gemara rejects this: The verse states: “The daughter of your father’s wife,” and this means whoever can enter a marriage bond with your father. This excludes his sister from a Canaanite maidservant or gentile woman, with whom no marital bond is possible.

The Gemara asks: Since the verse rendering his sister forbidden both includes and excludes cases, what did you see as a reason to include a daughter from a woman who is forbidden and both parties are liable to receive karet, and to exclude the daughter of a Canaanite maidservant or gentile woman? The Gemara answers: It stands to reason that those relationships that are forbidden because they render both parties liable to receive karet should be included, since in general betrothal can come into effect with them. This is because although this woman is forbidden to his father, she is nevertheless permitted to other men.

The Gemara rejects this: On the contrary, it should include a Canaanite maidservant or a gentile woman, as, if she converts, betrothal can come into effect with the father himself. The Gemara answers: When she converts, she is considered like a different body, i.e., a new person, but when she was a gentile there was no possibility of marital relations with her. Therefore, the verse excludes her.

The Gemara asks: And with regard to the Rabbis, who infer a different matter from the verse “your father’s wife’s nakedness,” from where do they derive the halakha to exclude one’s sister from a Canaanite maidservant or gentile woman? The Gemara answers: They derive it from that which was said with regard to a Canaanite maidservant who was married to a Hebrew slave: “The wife and her children shall be her master’s” (Exodus 21:4). From here they learn that the lineage of the maidservant’s children is connected only to their mother and not at all connected to their Jewish father.

The Gemara asks: And why does Rabbi Yosei, son of Rabbi Yehuda, not learn this from here? The Gemara responds: One verse was necessary to teach the case of a Canaanite maidservant, and one verse was necessary to teach the case of a gentile woman. And both verses are necessary, as, if the Torah taught us only about a Canaanite maidservant, one could say she is excluded only because she does not have a pedigree, since the Torah ascribes no family relationships to maidservants, but with regard to a gentile woman who does have a pedigree, say no. It was therefore necessary to say that one’s daughter by a gentile woman does not have the legal status of a daughter.

Conversely, if it would teach us only the case of a gentile woman, one might say that this is because she does not have any connection with the mitzvot and therefore her children are in no way Jewish. But since a Canaanite maidservant has a connection with the mitzvot, as she is obligated to observe the prohibitions in the same way as a Jewish woman, say no, i.e., her children should be considered children of their Jewish father. Therefore, this additional proof is necessary.

The Gemara asks: And according to the opinion of the Rabbis, we found a source that the children of a Canaanite maidservant are not considered the children of their Jewish father, but from where do we derive that children born to a Jewish father by a gentile woman are not considered his children? And if you say: Let us derive it from the case of the Canaanite maidservant, it has already been shown that these are both necessary, and one cannot be derived from the other.

The Gemara answers: Rabbi Yoḥanan said in the name of Rabbi Shimon ben Yoḥai: The verse states: “Neither shall you make marriages with them: Your daughter you shall not give unto his son, nor his daughter shall you take unto your son, for he will turn away your son from following Me” (Deuteronomy 7:3–4). This teaches that your son born from a Jewish woman is called your son, but your son born from a gentile woman is not called your son, but her son. The verse teaches that since the son of a gentile woman is her son alone, he is not considered related at all to his Jewish father.

Ravina said: Conclude from here that the son of your daughter by a gentile father is nevertheless called your son, i.e., grandson. The Gemara asks: Shall we say that Ravina holds that if a gentile or slave engaged in intercourse with a Jewish woman, the offspring is of unflawed lineage? The Gemara answers: There is no conclusive proof from here, because granted, she is not a mamzer, but nevertheless she is still not of unflawed lineage; rather, she is called a Jew who is unfit to marry into the priesthood.

The Gemara asks with regard to Rabbi Shimon’s reasoning: Was this verse not written in relation to the seven nations who inhabited the land of Canaan when Joshua entered Eretz Yisrael but not with regard to other nations? The Gemara responds that the words “He will turn away” comes to include all those who would turn one’s grandson away from God, i.e., any gentile.

The Gemara asks: This works out well for Rabbi Shimon, who interprets the rationale behind the mitzva in the verse and draws halakhic conclusions based on that interpretation. Although the verse is stated with regard to the seven nations, the reason for the verse applies to all other gentile nations. However, according to the opinion of the Rabbis, who do not draw inferences from the rationale of the verse to apply this ruling to all other nations, from where do they derive this halakha? The Gemara answers: Who is the tanna who disagrees with Rabbi Yosei, son of Rabbi Yehuda? It is Rabbi Shimon, who applies the rationale of the verse to all other nations.