the matter depends upon days, not blood. Although the flow of blood causes her to become impure, she remains impure for a full seven days regardless of whether she continues to experience menstrual bleeding for the duration of that time period. Similarly, in the case of a brother’s wife, the Merciful One makes her forbidden status dependent upon children, as, if she has children she remains forbidden to her husband’s brother even after her husband dies.

Rather, the Gemara refutes the derivation in the following manner: What comparison can be drawn from a menstruating woman and a brother’s wife, which are unique in that what renders them prohibited does not render them permitted? Each becomes permitted due to an external factor, i.e., the passing of seven days or the death of her childless husband. Can you say that the halakhot of these cases apply to a married woman, whose prohibited status is different in that the one who renders her prohibited to the rest of the world, i.e., her husband, has the capacity to render her permitted through divorce?

Rather, the Gemara offers another source for the halakha that the initial stage of intercourse is considered sexual intercourse. Rabbi Yona said, and some say it was Rav Huna, son of Rav Yehoshua: The verse states at the end of the chapter on forbidden relations: “For whoever shall do any of these abominations, the souls that do them shall be cut off” (Leviticus 18:29). All those with whom relations are forbidden are compared to each other in this verse, and therefore also to a menstruating woman, who is mentioned in that chapter. Consequently, just as one is liable to receive punishment for having sexual intercourse with a menstruating woman from the time of the initial stage of intercourse, so too, one violates all prohibitions against engaging in forbidden relations from the time of the initial stage of intercourse.

The Gemara further asks: But if that is the source of this halakha, why do I need the term nidda that is written with regard to a brother’s wife? The Gemara answers that it is needed for that which Rav Huna taught, as Rav Huna said: From where in the Torah is there a hint to the halakha of a yevama? The Gemara expresses surprise: From where? Isn’t it written explicitly in the verse “Her brother-in-law will have intercourse with her” (Deuteronomy 25:5)? Rather, Rav Huna meant to say: From where is there a hint that a yevama is forbidden to her brother-in-law in her husband’s lifetime, even after she is divorced from her husband?

The Gemara remains puzzled: No proof is needed for this halakha either, as this is based upon logical reasoning: From the fact that the Merciful One says the woman is permitted to her brother-in-law after her husband’s death it may be inferred that in her husband’s lifetime she is forbidden to him.

The Gemara refutes this argument: Perhaps after her husband’s death it is a mitzva for her brother-in-law to marry her, whereas during her husband’s lifetime their marriage is optional. Alternatively, perhaps after her husband’s death, yes, she is permitted to him, while during her husband’s lifetime, no, they are not permitted to marry, but there is no punishment of karet if they do. This is because the source of the prohibition is the mitzva for them to marry after the husband’s death, and a prohibition that stems from a positive mitzva has the status of a positive mitzva, but nothing more.

Therefore, the verse states: “And if a man shall take his brother’s wife, it is impurity [nidda]” (Leviticus 20:21). Is his brother’s wife necessarily a menstruating woman [nidda]? Rather, she is like a menstruating woman in the following manner: Just as with regard to a menstruating woman, although she has a permitted stage afterward, at the time that she is forbidden, one who has intercourse with her is liable to receive the punishment of karet, so too, with regard to a brother’s wife, although she has a permitted stage afterward, during her husband’s lifetime marriage to her brother-in-law is punishable by karet.

The Gemara asks: But if the source of the halakha that the initial stage of intercourse is considered sexual intercourse is as stated above, why do I need this halakha to be indicated by the word he’era (Leviticus 20:19) in the case of a father’s sister and a mother’s sister?

The Gemara answers that it is needed for the dilemma that Ravina raised before Rava: With regard to one who performs the initial stage of intercourse with another male, what is the halakha? Is it considered to be a forbidden act of homosexual intercourse? The Gemara is puzzled by this dilemma: With regard to a male, it is written explicitly: “You shall not lie with a man as with a woman” (Leviticus 18:22), which indicates that anything considered an act of sexual intercourse with a woman is also considered an act of sexual intercourse with a man.

Rather, the word he’era in the case of a father’s sister and a mother’s sister is needed to resolve the following dilemma: With regard to one who performs the initial stage of intercourse with an animal, what is the halakha? Rava said to Ravina: If the word he’era does not refer to the matter of the initial stage of intercourse in the context where it is written, i.e., the prohibition with regard to a father’s sister and a mother’s sister, as this halakha is derived from a comparison based upon the statement of Rabbi Yona, refer it to the matter of the initial stage of intercourse with an animal. The superfluous expression written in the case of a father’s sister and a mother’s sister teaches that the initial stage of intercourse is considered sexual intercourse even with an animal.

The Gemara asks: Since intercourse with an animal is a prohibition for which one is liable to receive capital punishment from the court, what is the reason that the halakha of the initial stage of intercourse that applies to it is written with regard to the prohibitions proscribing a father’s sister and a mother’s sister, for which one is liable to receive karet? Let the word he’era be written with regard to prohibitions for which one is liable to receive capital punishment from the court, and let us derive the halakha with regard to a prohibition punishable by capital punishment from the court, i.e., the case of bestiality, from another prohibition punishable by capital punishment from the court.

The Gemara answers: Since the entire verse of a father’s sister and a mother’s sister comes for the purpose of an exposition, as the Gemara is about to explain, this matter, i.e., that the initial stage of intercourse is considered intercourse, is also written for the purpose of an exposition, i.e., to indicate that this principle holds true in a different context, i.e., that of bestiality.

The Gemara asks: What is the exposition that the rest of the verse introduces? As it is taught in a baraita, the verse “You shall not uncover the nakedness of your father’s sister” (Leviticus 18:12) indicates that the prohibition applies whether she is your father’s sister from his father, or from his mother. Do you say that she is forbidden whether she is your father’s sister from his father or from his mother, or perhaps it is only a sister from his father who is forbidden, but not from his mother?

It may be inferred logically from the fact that the Torah rendered him liable here and rendered him liable with his sister: Just as with regard to his sister he is liable to receive punishment whether she is his sister from his father or from his mother, so too here, he is liable whether she is his father’s sister from his father or from his mother.

Or perhaps go this way and compare a father’s sister and a mother’s sister to a different halakha: The Torah rendered him liable here and rendered him liable with his aunt, i.e., the wife of his father’s brother: Just as concerning his aunt, he is liable to receive punishment only with regard to the wife of his father’s brother from his father, i.e., the wife of his father’s paternal brother, and not for the wife of his father’s brother from his mother, i.e., the wife of his father’s maternal brother, so too here, he is liable only with regard to a father’s sister or a mother’s sister from their father, i.e., a paternal sister, and not from their mother, a maternal sister.

The Gemara analyzes these two possibilities: Let us see to which case it is more similar, i.e., which is a better comparison. We should derive the halakha with regard to a prohibition that comes on its own, i.e., a father’s sister and a mother’s sister, from a prohibition that also comes on its own, i.e., a sister, and the halakha with regard to his aunt cannot be used to prove otherwise, as it is not a prohibition that comes on its own, but through marriage.

The Gemara counters this argument: Or perhaps go this way and claim that we should derive the halakha with regard to the relatives of his father, i.e., his father’s sister, from the halakha with regard to the relatives of his father, i.e., his father’s brother’s wife, and the case of his sister cannot be used to prove otherwise, as she is his own relative. Consequently, there is no conclusive proof based on reasoning alone.

Therefore the verse states: “You shall not uncover the nakedness of your father’s sister,” which teaches that this prohibition applies whether she is your father’s sister from his father or from his mother. Similarly, the verse “You shall not uncover the nakedness of your mother’s sister” indicates that the prohibition applies whether she is your mother’s sister from her father or from her mother. These prohibitions are stated twice (Leviticus 18:12–13 and 20:19), and the superfluous verse indicates that the prohibition applies even to the maternal sister of one’s father or mother.

The Gemara asks: Why do I need the Torah to write this halakha with regard to a father’s sister, and why do I need the Torah to write it again with regard to a mother’s sister? Rabbi Abbahu said: Both verses are necessary. If the Merciful One had written this halakha only with regard to one’s father’s sister, one might say that it is limited to that case, as she has common lineage with her nephew, since lineage goes through one’s father. However, with regard to one’s mother’s sister you might say that she is not prohibited, as she is not considered to share common lineage with him.

And conversely, if the Merciful One had written this halakha only with regard to one’s mother’s sister, one might say that it is limited to that case, as she is certainly his relative, since one’s biological relationship with his mother is absolutely certain. However, with regard to one’s father’s sister, one might say no, that she is not forbidden, as paternity can never be established beyond doubt. It is therefore necessary for this halakha to be stated in both cases.

The Gemara asks: And with regard to his aunt, where it is obvious to the tanna that the prohibition includes only the wife of his father’s brother from his father and not from his mother, from where does he derive this halakha?

Rava said: It is derived through a verbal analogy between the terms “his uncle” and “his uncle.” It is written here: “He has uncovered his uncle’s nakedness” (Leviticus 20:20), and it is written there, with regard to the redemption of a Jew who has been sold to a gentile: “Either his uncle or his uncle’s son shall redeem him” (Leviticus 25:49). Just as there, in the case of redemption, it must be a relative from the side of his father and not from the side of his mother, so too here, with regard to forbidden relations, the prohibition applies to the wife of his father’s brother from his father, i.e., the wife of his father’s paternal brother, and not from his mother.

The Gemara asks: And there, with regard to the halakhot of redemption, from where do we derive that a maternal relative is not included? The verse states: “Or any that is near of kin to him of his family shall redeem him” (Leviticus 25:49), and it is an established principle that only the family of one’s father is called family, while the family of one’s mother is not called family, as lineage is determined based upon one’s father.

And with regard to that which we learned in a mishna: If they said to him: Your wife is dead, and he then married her sister from her father. He was subsequently informed that his second wife died, and he married her sister from her mother, i.e., his second wife’s maternal sister. He was then informed that his third wife died, and he married her sister from her father, i.e., his third wife’s paternal sister. He was then informed that his fourth wife died, and he married her sister from her mother, i.e., his fourth wife’s maternal sister. It later became apparent that all these rumors were unfounded and all the women were still alive. Consequently, since one cannot marry his wife’s sister during his wife’s lifetime, some of the marriages are void.

The halakha in this case is that it is permitted for him to marry his first, third, and fifth wives, as they are not related to each other. Consequently, these marriages are valid, and these women exempt their rival wives from levirate marriage if they all became subject to levirate marriage and one of them performed levirate marriage or ḥalitza. However, it is prohibited for him to marry his second and fourth wives, as they are both sisters of one of his previous wives, and their marriages are therefore void. Consequently, sexual intercourse between one of them and his brother, if he has died childless, does not exempt her rival wife, i.e., the real wives of the deceased, from levirate marriage.

And if the first wife indeed died, and he had intercourse with the second woman after the death of the first one, it is permitted for him to marry the second and fourth women, who are not related to each other, and they exempt their rival wives from levirate marriage if they perform levirate marriage or ḥalitza, and it is prohibited for him to marry the third and fifth women, as they are sisters of his previous wives, who are still alive, and consequently these marriages are void.