The Mishnah presents a case of four brothers married to four women who are not sisters, and all four brothers die. If the oldest remaining brother wishes to perform levirate marriage, known as Yibum, with all four women, he may. The Gemara clarifies that this scenario implies there are at least five brothers, with four having died, leaving one to perform Yibum with all four widows. The Gemara questions whether he is permitted to take four wives, citing a passage from the Torah that describes the court advising a levirate brother, or Yavam, against marrying a woman who is significantly older or younger than him, to prevent marital strife. This suggests that the rabbis prioritize a harmonious marriage. How, then, could they permit a man to marry four wives, which would be difficult to support and maintain peace in the household?
The Gemara responds that the Mishnah refers to a man who has the financial means to support four wives. However, the Gemara then asks why the Mishnah limits the number to four; why not more? The Gemara explains that four is the maximum number of wives a man can marry while still fulfilling his conjugal obligations, known as Onah, to each wife. For a Torah scholar, the Onah is once a week. With four wives, he can fulfill this obligation to each wife every four weeks. More than four wives would make it impossible to meet this obligation. This understanding is derived by the Sages from the verse, "who gives it in its proper time."
The Mishnah then discusses a case where a man was married to two women and died. The Yavam performs either Yibum or Halitza (a ritual release from levirate marriage) with one of the wives, and the other is automatically released. The Gemara asks for the source that only one procedure is needed. It cites a verse that states, "he who does not want to build his brother's house," implying that only one "house" is built, meaning the obligation extends to only one of the women. Therefore, performing Yibum on both is not an option. The Gemara further clarifies that performing Halitza on both is also not an option, as the Torah uses the singular term "house" in reference to Halitza.
The Gemara then considers whether the Yavam could perform Yibum on one woman and Halitza on the other. A general rule is derived: a woman who is subject to Yibum can also be subject to Halitza, but a woman not subject to Yibum cannot be subject to Halitza. Since it was established that Yibum cannot be performed on both women, the other woman is not subject to Yibum, and therefore not subject to Halitza. Thus, performing Yibum on one and Halitza on the other is not an option. The Gemara offers an additional reason: there is a concern that if we permit this, a man might first perform Halitza and then Yibum. Once Halitza is performed, the woman is forbidden to the Yavam, and any subsequent union would be forbidden. Therefore, to prevent this potential transgression, performing both Yibum and Halitza is not allowed, even if Yibum is done first.
The Gemara then suggests that perhaps the obligation of Yibum only applies when there is one widow, and not when there are two. The phrase "one house" might imply this limitation. However, the Gemara refutes this by referencing the concept of Sarat Irva, where one of the wives is a forbidden relative (an Irva) and the other is permissible. If Yibum did not apply to two women, there would be no need for a special teaching that the permissible wife of an Irva is also forbidden. The Gemara explains that without this teaching, one might mistakenly think that since the Irva is excluded, the remaining permissible wife is considered a single widow, making her subject to Yibum. Therefore, the teaching of Sarat Irva proves that Yibum applies even when there are multiple women, though not on all of them. The repeated use of the word "his Yevama" in the Torah indicates that Yibum applies even when two women are involved. Consequently, the Yavam performs Yibum on one, and the other is released without any procedure, either due to the rule that a woman not subject to Yibum is not subject to Halitza, or due to the concern of performing Halitza before Yibum.
The Mishnah then presents a case where a man was married to two women: one who was fit for the priesthood (Keshera L'Kehuna) and one who was a divorcee (Gerusha), and thus unfit for the priesthood (Pesula L'Kehuna). If he dies, the Yavam should perform Yibum with the Keshera or Halitza with the Pesula. This prevents making the Keshera woman, who could otherwise marry a priest, forbidden to a priest by performing Halitza with her. Rabbi Yosef comments that this Mishnah illustrates the principle: "A person should not spill his water when others may need it." One should not spoil something for others if they can benefit from it. Therefore, one should perform Halitza on the woman already unfit for the priesthood, leaving the fit woman available for a priest.
The next Mishnah discusses cases where a child born from a forbidden union is a Mamzer (a child of an illicit union). According to Rabbi Akiva, a child is a Mamzer even from a transgression that carries a negative commandment (Chayavei Lavin). The Mishnah lists examples: a man who remarries his divorced wife after she married someone else in the interim, a man who marries his Halutza (a woman released through Halitza), and a man who marries a relative of his Halutza (e.g., her sister). In all these cases, Rabbi Akiva states that the man must divorce the woman, and the child is a Mamzer. The Sages, however, generally hold that Mamzerut only results from transgressions punishable by spiritual excision (Karet). However, the Sages agree that if a man marries a relative of his divorced wife (e.g., her sister while his wife is still alive), which is a transgression punishable by Karet, the child is a Mamzer. This is because a divorced wife is still considered "like his wife" regarding forbidden relatives.
The Gemara questions if Rabbi Akiva indeed holds that marrying a relative of his Halutza results in a Mamzer. Rabbi Resh Lakish taught that marrying a relative of a Halutza is only forbidden by rabbinic decree (Isur Rabbanan). How can a child from a rabbinically forbidden union be a Mamzer? The Gemara concludes that the Mishnah's text must be amended. Instead of "relative of his Halutza," it should read "relative of his divorced wife" (Kerovat Gerushato). This makes sense because the Sages agree with Rabbi Akiva regarding Kerovat Gerushato, as stated in the Mishnah's conclusion: "The Sages agree with Rabbi Akiva regarding Kerovat Gerushato that the child is a Mamzer." This agreement would be illogical if Rabbi Akiva had not mentioned Kerovat Gerushato in the first place.
The Gemara then considers an alternative interpretation: perhaps Rabbi Akiva did not mention Kerovat Gerushato, and the Sages' statement is an independent teaching that a child born from a transgression punishable by Karet is a Mamzer. However, this is already taught in a later Mishnah by Rabbi Shimon HaTimni. The Gemara replies that this Mishnah establishes this as an undisputed ruling (Stam Mishnah), not merely Rabbi Shimon HaTimni's individual opinion. The Gemara then asks why, if the Sages are teaching a general rule about Karet leading to Mamzerut, they single out Kerovat Gerushato. The Gemara concludes that the original emendation is correct: Rabbi Akiva indeed mentioned Kerovat Gerushato in the first part of the Mishnah, and the Sages' agreement refers to his statement.
The Gemara returns to the initial question: why is a child from a relative of a Halutza considered a Mamzer if it's only a rabbinic prohibition? The Gemara explains that Rabbi Akiva holds that a Halutza is considered "his house" (Beito), like a wife. Therefore, her relatives are forbidden by Torah law, just like a divorced wife's relatives. This means that for Rabbi Akiva, marrying a relative of a Halutza is a Torah prohibition, leading to Mamzerut.
Rabbi Yosef, in the name of Rabbi Shimon ben Lakish, states that everyone agrees that in the case of a man who remarries his divorced wife, the child born from this union is "blemished for the priesthood" (Pagum L'Kehuna). This means that if the child is a girl, she is a Halala, unfit to marry a priest. The Gemara clarifies that "everyone agrees" refers to Rabbi Shimon HaTimni, who, while not considering such a child a Mamzer (as it's only a negative commandment, not Karet), still agrees that the child is Pagum L'Kehuna. Rabbi Akiva would certainly agree, as he considers the child a Mamzer, which implies being Pagum L'Kehuna.
Rabbi Shimon HaTimni's reasoning for this "blemish" is a logical deduction (Kal V'Chomer) from the case of a widow (Almana) who marries a High Priest (Kohen Gadol). An Almana is permitted to other priests, but forbidden to a Kohen Gadol. If she marries a Kohen Gadol, her child is a Halal, Pagum L'Kehuna. The Kal V'Chomer argues: if an Almana, whose prohibition is not universal among priests, produces a Pagum L'Kehuna child when marrying a Kohen Gadol, then a woman who remarries her divorced husband, a prohibition that applies to everyone, should certainly produce a Pagum L'Kehuna child. The Gemara rejects this Kal V'Chomer, arguing that the Almana's case is more severe because she herself becomes a Halala (unfit for the priesthood) by marrying a Kohen Gadol. In contrast, a divorced woman who remarries her former husband does not become more unfit for the priesthood, as she was already a Gerusha (divorcee) and thus already unfit. Therefore, the Kal V'Chomer from Almana is not valid.
The Gemara offers a second reason to reject the statement that the child is Pagum L'Kehuna in the case of a man who remarries his divorced wife. The Torah states about this union, "it is an abomination" (To'eva Hi). The Gemara interprets this to mean that "she is an abomination, but her children are not abominations," implying that her children are fit for the priesthood. The Gemara then reinterprets "she is an abomination, but her children are not abominations" to mean "she is an abomination, but her co-wife (Tzara) is not an abomination." This means that her co-wife would still be subject to Yibum, but her children are indeed abominations (To'avim), meaning Pesulei Kehuna (unfit for priesthood). This reinterpretation allows the original statement that the child is Pagum L'Kehuna to stand.
A third proof is brought from a Braita (a teaching from the Mishnaic period not included in the Mishnah) which states that in the cases of a man who remarries his divorced wife, marries his Halutza, or marries a relative of his Halutza, Rabbi Akiva says the marriage is not valid (Kiddushin Lo Tofes), and the woman does not need a divorce document (Get). She is unfit (Pesula), and her child is unfit (Valda Pesul). The Sages, however, say that the marriage is valid (Kiddushin Tofes), she needs a Get, and both she and her child are fit (Keshera).
The Gemara then analyzes the Sages' statement: "she is fit and her child is fit." If "fit" means fit for the general community (Kahal), it is obvious. Thus, "fit" must mean fit for the priesthood (Kehuna). This would imply that a child from a transgression of a negative commandment is fit for the priesthood, contradicting the initial statement that such a child is Pagum L'Kehuna. The Gemara responds that "she is fit" refers to her being fit for the priesthood (as she is not a Zona, a harlot), while "her child is fit" refers to the child being fit for the general community (not a Mamzer), but still Pagum L'Kehuna. The Gemara supports this distinction by noting that Rabbi Akiva's statement in the first part of the Braita also uses "unfit" in two different senses: the mother is unfit for the priesthood (as a Zona), and the child is unfit for the community (as a Mamzer).
Thus, the third proof against the child being Pagum L'Kehuna is also rejected. The Gemara then returns to the first rejection of the Kal V'Chomer from Almana. That rejection stated that an Almana is worse because she herself becomes a Halala, whereas a divorced woman who remarries her former husband does not become more unfit for the priesthood. The Gemara re-examines this. It states that if the original statement is changed to refer to a man who cohabits with a woman forbidden by Karet, then "everyone agrees" that the child is Pagum L'Kehuna. "Everyone" here includes Rabbi Yehoshua, who holds that Mamzerut only comes from transgressions punishable by a court (Chayavei Beit Din). Even for Rabbi Yehoshua, while the child is not a Mamzer, it is still Pagum L'Kehuna. This is proven by the same Kal V'Chomer from the Almana marrying a Kohen Gadol. The previous rejection of this Kal V'Chomer (that the Almana herself becomes a Halala, while the divorced woman does not) is now addressed: a woman who cohabits with a man forbidden by Karet also becomes a Zona, and thus Pesula L'Kehuna. Therefore, the Kal V'Chomer holds: if an Almana, whose prohibition is not universal, produces a Pagum L'Kehuna child, then a woman forbidden by Karet, whose prohibition is universal, certainly produces a Pagum L'Kehuna child. The counter-argument that the Almana is worse because she herself becomes a Halala is nullified, as the woman in the Karet case also becomes Pesula L'Kehuna by becoming a Zona.
The Gemara then clarifies why the argument about the woman becoming a Zona and thus Pesula L'Kehuna does not apply to the case of a man who remarries his divorced wife. In that case, the woman was already a Gerusha and thus already Pesula L'Kehuna. Her remarriage to her former husband does not make her "more unfit" for the priesthood. Furthermore, she is not considered a Zona in the context of a daughter of a priest (Bat Kohen) eating Teruma (sacred food). The Torah defines a Zona who cannot eat Teruma as someone who committed an act of promiscuity with a man she was always forbidden to. However, a divorced woman was permitted to her first husband, and her remarriage to him is only a negative commandment. Therefore, she is not considered a Zona in this specific context, and her status regarding the priesthood does not change. Thus, the Kal V'Chomer from the Almana is still invalid for the case of a man who remarries his divorced wife, but it is valid for the case of a man who cohabits with a woman forbidden by Karet, where the child is indeed Pagum L'Kehuna.