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The Rambam’s view · Bekhorot 47 · בכורות מ״ז
Lineage, Conversion, and the Sanctity of the Firstborn
How the Rambam determines the halakhic status of converts' children and firstborn sons born from mixed unions.
Conversion and Prior Lineage
The Gemara discusses how conversion transforms pre-existing familial relationships. Does a convert who fathered children while still a gentile fulfill the mitzvah of פריה ורביה (procreation)?
Rabbi Yochanan teaches that he has fulfilled the mitzvah, because he contributed to populating the world. Reish Lakish counters that a convert is legally regarded as a newborn child, erasing past ties.
Procreation Requires Joint Conversion
The Rambam rules firmly with Rabbi Yochanan against Reish Lakish. A convert fulfills procreation through children born prior to conversion, provided that both he and the children convert.
Maggid Mishneh notes that the halakha follows Rabbi Yochanan, but explains why the Rambam added a condition. Rabbi Yochanan would not consider the obligation fulfilled if the children remained idol worshippers, so the children must convert alongside their father.
By contrast, an emancipated slave never fulfills procreation through children born during servitude. An enslaved person possesses no recognized halakhic lineage (ייחוס - yichus),.
הָיוּ לוֹ בָּנִים בְּגֵיוּתוֹ וְנִתְגַּיֵּר הוּא וְהֵם הֲרֵי זֶה קִיֵּם מִצְוָה זוֹ.When he had fathered children as a gentile, and both he and they convert, he is considered to have fulfilled this mitzvah. (Mishneh Torah, Marriage 15:6)
Firstborn Sons of Consecrated Mothers
The Gemara also examines the obligation of פדיון הבן (redemption of the firstborn) when a Levite or priestly woman conceives from a gentile,. Because the father is a gentile, halakhic lineage cannot pass through him.
The Rambam establishes that the mother's status determines whether the child is obligated in redemption. A Levite woman's son is exempt, whereas a priestly woman's son is obligated.
Kessef Mishneh confirms that this ruling codifies the debate between Rav Adda bar Ahava and Rav Pappa on our daf.
לְוִיָּה הַמְעֻבֶּרֶת מֵעַכּוּ"ם בְּנָהּ פָּטוּר. וְכֹהֶנֶת הַמְעֻבֶּרֶת מֵעַכּוּ"ם בְּנָהּ חַיָּב שֶׁהֲרֵי נִפְסְלָה אִמּוֹ מִן הַכְּהֻנָּה בִּבְעִילַת הָעַכּוּ"ם:When a Levite woman was impregnated by a gentile, her son is exempt. If a woman of the priestly family was impregnated by a gentile, her son is obligated, for his mother was disqualified from the priestly family because of relations with the gentile. (Mishneh Torah, First Fruits and other Gifts to Priests Outside the Sanctuary 11:11)
Tribal Status and Forbidden Relations
Kiryat Sefer clarifies the mechanism behind the Rambam's distinction. A gentile father lacks lineage, so the child's identity stems from the Jewish mother.
A Levite woman does not forfeit her tribal identity through forbidden intercourse. Even if captured or subjected to illicit relations, she remains entitled to consume מעשר ראשון (first tithe).
By contrast, intercourse with a gentile profanes a priestly daughter, turning her into a disqualified non-priestess,. Because she loses her priestly sanctity, her firstborn son cannot claim exemption and must redeem himself.
לְפִיכָךְ בַּת לֵוִי שֶׁנִּשְׁבֵּית אוֹ שֶׁנִּבְעֲלָה בְּעִילַת זְנוּת נוֹתְנִין לָהּ הַמַּעֲשֵׂר וְאוֹכֶלֶת.For this reason, when the daughter of a Levite has been taken captive or she engaged in forbidden relations, she can be given tithes and she may partake of it. (Mishneh Torah, Tithes 1:2)
Practical Halakha and Personal Status
In practical halakha, the child of any Jewish woman impregnated by a gentile is כשר (kasher - halachically fit). The child inherits the mother's status completely.
A Levite woman's son never undergoes redemption, whereas a profaned priestess's son must pay five sela coins to a כהן (priest).
Regarding family continuity, a convert achieves fulfillment of procreation only when the children enter the covenant together.
A mother transmits her tribal exemption from redemption unless forbidden relations strip her of her sanctity, while a convert fulfills procreation only if his children join the covenant.