The Mishnah begins by asking, "What defines a mamzer?" It states that any relative with whom one is forbidden to marry due to a prohibition, even if not punishable by karet, can produce a mamzer. An example given is a woman who was forced by one's father. According to Rabbi Yehuda, the verse "one shall not uncover his father's nakedness" refers to this specific scenario, where one is forbidden to marry a woman his father forced. This is a prohibition rooted in kinship. Another example is marrying a woman one has performed halitza with; while there is a prohibition against it, it is not punishable by karet. In such cases, Rabbi Akiva rules that the child is a mamzer.
A second opinion is offered by Shimon HaTimni, who states that a mamzer is only produced from a relationship punishable by karet at the hands of Heaven. The Mishnah concludes that the law follows Shimon HaTimni. Thus, according to Shimon HaTimni, a child born from a man marrying a woman he performed halitza with would not be a mamzer, as this is only a prohibition, not a karet offense. For Shimon HaTimni, it must be a karet prohibition.
Rabbi Yehoshua presents a third view, asserting that a mamzer is only produced from a relationship punishable by a court-imposed death penalty, such as a man with a married woman. Thus, we have a three-way dispute regarding what constitutes a mamzer: Rabbi Akiva holds it is any forbidden kinship, Shimon HaTimni limits it to relationships punishable by karet, and Rabbi Yehoshua restricts it to relationships punishable by a court-imposed death penalty.
The Mishnah continues with Shimon ben Azai, who recounts, "I found a scroll of lineages in Jerusalem, and it was written there: 'So-and-so is a mamzer from a married woman.'" This statement supports Rabbi Yehoshua's opinion. Shimon ben Azai's finding in Jerusalem, confirming a mamzer from a married woman, directly aligns with Rabbi Yehoshua's view that only a relationship punishable by a court-imposed death penalty produces a mamzer.
The Mishnah then presents several cases concerning marriage prohibitions. If a man's wife dies, he is permitted to marry her sister. The prohibition against marrying a wife's sister applies only while his wife is alive. Similarly, if he divorced his wife and she subsequently died, he is permitted to marry her sister. The crucial point in these cases is that the sister becomes permissible only after the wife's death; divorce alone is not sufficient. Even if the divorced wife remarried and then died, only then is her sister permitted to him. The same principle applies to a yevamah: if a man performed yibum with a woman and she died, he is permitted to marry her sister. Just as a wife's sister becomes permissible after death, so too does a yevamah's sister. The Mishnah reiterates that even if the yevamah remarried after the yibum and then died, her sister only becomes permissible after her actual death.
The Gemara now analyzes the reasoning behind Rabbi Akiva's opinion that a mamzer results from any forbidden relationship. It cites a verse in Deuteronomy: "A man shall not take his father's wife, nor uncover his father's nakedness." The Gemara explains that "uncover his father's nakedness" refers to a woman his father forced. Rabbi Yehuda interprets this verse as prohibiting relations with a woman his father forced, which is a prohibition based on kinship. The Gemara connects this to the subsequent verse, which discusses the law of mamzerut. The proximity of these verses suggests that only relationships like that of a father's forced woman, which involves a prohibition based on kinship, can produce a mamzer. Thus, Rabbi Akiva derives his ruling from the juxtaposition of these verses: "one shall not uncover his father's nakedness" (referring to a father's forced woman, a prohibition) and "a mamzer shall not enter the congregation of God." This implies that such a relationship, which is a prohibition, can result in a mamzer.
The Gemara then introduces other interpretations of Rabbi Akiva's view. Rabbi Simai and Rabbi Yeshbab extend Rabbi Akiva's opinion beyond kinship-based prohibitions. Rabbi Simai includes cases where the prohibition is not due to kinship, such as a man marrying his divorcée after she married someone else. This is a prohibition, but not based on a family relationship. Rabbi Yeshbab further expands it to include even positive commandments that imply a prohibition, like marrying an Egyptian before the third generation of converts. The Gemara explains that the extra "and" in the verse "and he shall not uncover his father's nakedness" serves to include these additional cases in Rabbi Akiva's ruling. This extra "and" extends the scope of mamzerut to other types of prohibitions, whether they are not kinship-based (according to Rabbi Simai) or even positive commandments with a prohibitive aspect (according to Rabbi Yeshbab).
At this point, the Gemara identifies five distinct opinions regarding mamzerut: 1. Rabbi Akiva, as understood by Rabbi Yeshbab: A mamzer results from any prohibition, even a positive commandment that implies a prohibition. 2. Rabbi Akiva, as understood by Rabbi Simai: A mamzer results from any prohibition, even if not kinship-based. 3. Rabbi Akiva, as understood in the Mishnah: A mamzer results from a kinship-based prohibition. 4. Shimon HaTimni: A mamzer results only from a relationship punishable by karet. 5. Rabbi Yehoshua: A mamzer results only from a relationship punishable by a court-imposed death penalty.
The Gemara then explains Shimon HaTimni's reasoning. He interprets the verse "one shall not uncover his father's nakedness" as referring to a woman who falls to his father for yibum (his father's brother's wife), a relationship punishable by karet. The subsequent verse about mamzerut then teaches that a mamzer comes specifically from such a karet offense. This interpretation aligns with the Rabbanan's view.
Next, the Gemara addresses Rabbi Yehoshua's opinion, which holds that mamzerut only arises from relationships punishable by a court-imposed death penalty. Rabbi Yehoshua questions why the Torah would include the beginning of the verse, "A man shall not take his father's wife," if the end of the verse, "nor uncover his father's nakedness," was meant to teach about mamzerut from lesser prohibitions (as per Rabbi Akiva or Shimon HaTimni). The beginning of the verse, "A man shall not take his father's wife," refers to a woman his father married through kiddushin, a relationship punishable by a court-imposed death penalty. Rabbi Yehoshua argues that the novelty of the verse is that mamzerut applies only to the first part of the verse, i.e., cases punishable by a court-imposed death penalty. The latter part of the verse, "nor uncover his father's nakedness," according to Rabbi Yehoshua, is not connected to mamzerut at all. Instead, it serves a different purpose: either to teach that a man who has relations with his father's yevamah incurs two prohibitions, or, according to Rabbi Yehuda, to establish that a father's forced woman is indeed forbidden, but not to teach about mamzerut. Thus, for Rabbi Yehoshua, mamzerut is exclusively derived from the beginning of the verse, which refers to a relationship punishable by a court-imposed death penalty.
To summarize the three main opinions: Rabbi Akiva connects mamzerut to "uncover his father's nakedness" (a father's forced woman, a prohibition). Rabbi Simai and Rabbi Yeshbab extend this to other prohibitions, even non-kinship or positive commandments. Shimon HaTimni connects mamzerut to "uncover his father's nakedness" as referring to a father's yevamah (a karet offense). Rabbi Yehoshua derives mamzerut from "A man shall not take his father's wife" (a court-imposed death penalty offense), viewing the latter part of the verse as unrelated to mamzerut.
The Gemara then discusses cases where a child is not a mamzer, even if the relationship is forbidden. Everyone agrees that if a man has relations with a nidah (menstruating woman) or a sotah (a woman suspected of adultery), the child is not a mamzer. This is despite the fact that relations with a nidah are punishable by karet, and relations with a sotah are a prohibition. The reason is that in both cases, the kiddushin (marriage) is valid. A mamzer can only result from a relationship where kiddushin is not valid. The verse "and her impurity is upon him" implies that even during her state of nidah, kiddushin is valid. Similarly, with a sotah, the kiddushin remains binding, even though the husband is forbidden to her. Since the kiddushin is valid in these cases, the child is not a mamzer.
The Gemara adds a third case: a shomeret yavam (a woman whose husband died childless, awaiting yibum or halitza) who has relations with a man from the marketplace. Although this is a prohibition, according to Rabbi Akiva, one might expect the child to be a mamzer. However, the child is not a mamzer because kiddushin is valid in this case as well. The verse "the wife of the deceased shall not marry outside to a stranger" implies that if she does, the marriage is still a valid marriage. Therefore, in these three cases—nidah, sotah, and shomeret yavam who marries a stranger—the child is not a mamzer because kiddushin is valid.
Abaye, however, did not include the case of a shomeret yavam. The Gemara explains that Abaye was uncertain about the status of kiddushin in the case of a shomeret yavam, due to a dispute between Rav and Shmuel. According to Rav, when the verse says "she shall not be the wife of the deceased to a stranger," it means that kiddushin is not valid. Therefore, according to Rav, the child would be a mamzer. Shmuel, however, was uncertain; he thought it might mean that she should not do it, but if she does, the kiddushin is valid. Since Abaye was in doubt as to whether the law follows Rav or Shmuel, he did not include the shomeret yavam in his list of cases where the child is not a mamzer.
The Gemara returns to Shimon ben Azai's statement about finding the Megillat Yuhasin (scroll of lineages) in Jerusalem. A B'raita (external Mishnaic teaching) states that Shimon ben Azai found three things written in this scroll: 1. So-and-so is a mamzer because he was born from a married woman. 2. The Mishnayot of Rabbi Eliezer ben Yaakov are "measured and pure." This means Rabbi Eliezer ben Yaakov has few Mishnayot, but those few are clear and the law always follows them. 3. Hezekiah's son, Menashe, killed the prophet Yeshayahu.
The Gemara elaborates on how Menashe killed Yeshayahu. Menashe judged Yeshayahu as a false prophet. Menashe argued that Moshe Rabbeinu said, "No human can see God and live," yet Yeshayahu claimed to have seen God sitting on His throne. Secondly, Moshe Rabbeinu said that God is accessible at all times for prayer, while Yeshayahu said, "Seek God when He is found." Thirdly, Moshe Rabbeinu said that God fulfills one's allotted days, implying no addition, yet Yeshayahu told King Hezekiah that God would add fifteen years to his life. Based on these three points, Menashe concluded Yeshayahu was a false prophet.
Yeshayahu knew that Menashe would not accept his explanations and that attempting to justify himself would only lead to Menashe killing him intentionally. To avoid making Menashe a murderer by intent, Yeshayahu chose not to respond. Instead, he uttered one of God's holy names and was swallowed into a cedar tree. Menashe's men brought the cedar tree to him and cut it down. The Yerushalmi explains that they knew Yeshayahu was in the tree because his ritual fringes were hanging out. When the saw reached Yeshayahu's mouth, he died. This was a consequence of a sin Yeshayahu committed when he once spoke negatively about the Jewish people, calling them a "nation of impure lips." His mouth, therefore, was not sanctified and was vulnerable.
The Gemara then provides the answers to Menashe's challenges to Yeshayahu: 1. Regarding seeing God: Yeshayahu's vision was a lower level of prophecy, not the clear, face-to-face vision Moshe Rabbeinu experienced. Moshe Rabbeinu's level of clarity is impossible for a human to survive, but Yeshayahu's less clear vision was permissible. 2. Regarding seeking God: The verse stating God is available at all times refers to communal prayer. Yeshayahu's statement about seeking God "when He is found" refers to specific times when an individual's prayers are answered as readily as communal prayers. 3. Regarding adding years to life: This is a dispute between Rabbi Akiva and the Sages. Rabbi Akiva holds that God only fulfills a person's allotted days; if one is meritorious, they receive the full measure; if not, days are subtracted, but never added beyond the original decree. The Sages, however, contend that one can indeed gain extra years through merit. The Sages challenged Rabbi Akiva with the verse where Yeshayahu told Hezekiah that God would add fifteen years to his life. Rabbi Akiva responded that those fifteen years were already allotted to Hezekiah but were temporarily taken away due to his sins, and then restored. He proved this by citing the prophecy of a prophet in the time of Jeroboam, who prophesied the birth of Josiah, a descendant of David, long before Menashe (Hezekiah's son) was even born. Since Josiah was Menashe's grandson, Hezekiah must have had those years allotted to him from the beginning for Menashe and Josiah to be born. The Sages countered that the prophecy only said Josiah would be born from the house of David, not necessarily from Hezekiah. Thus, if Hezekiah had not received extra years, Josiah could have been born from another descendant of David. This remains a dispute on whether God adds years to a person's life beyond what was originally decreed, or merely restores what was temporarily withheld.