Kiddushin 67
גֵּר שֶׁנָּשָׂא מַמְזֶרֶת, דְּיֵשׁ קִידּוּשִׁין וְאֵין עֲבֵירָה – הַוָּלָד הוֹלֵךְ אַחַר הַפָּגוּם, דְּתַנְיָא: גֵּר שֶׁנָּשָׂא מַמְזֶרֶת – הַוָּלָד מַמְזֵר, דִּבְרֵי רַבִּי יוֹסֵי! אֲמַר לֵיהּ: מִי סָבְרַתְּ מַתְנִיתִין רַבִּי יוֹסֵי הִיא? מַתְנִיתִין רַבִּי יְהוּדָה הִיא, דְּאָמַר: גֵּר לֹא יִשָּׂא מַמְזֶרֶת, וְיֵשׁ קִידּוּשִׁין וְיֵשׁ עֲבֵירָה – הַוָּלָד הוֹלֵךְ אַחַר הַפָּגוּם.
there is the case of a convert who married a mamzeret, where there is a valid betrothal and there is no transgression, as they are permitted to marry each other, and yet the offspring follows the flawed lineage and is a mamzer. As it is taught in a baraita: With regard to a convert who married a mamzeret, the offspring is a mamzer. This is the statement of Rabbi Yosei. Rabbi Yoḥanan said to Rabbi Shimon: Do you maintain that the mishna is in accordance with the opinion of Rabbi Yosei? Not so; the mishna is in accordance with the opinion of Rabbi Yehuda, who says: A convert may not marry a mamzeret, and therefore in this case there is betrothal and there is a transgression, which is why the offspring follows the flawed lineage.
וְנִיתְנְיַיהּ! תְּנָא ״כׇּל מָקוֹם״ דְּסֵיפָא, לְאֵתוֹיֵי.
The Gemara asks: But if so, let the mishna teach this case as one of its examples. The Gemara answers: The mishna taught the principle: Any case where there is betrothal and a transgression, in the latter clause, precisely to include this kind of case. There is a guiding principle of the Gemara’s interpretation of the Mishna that a mishna does not include extraneous phrases. Every apparently superfluous phrase in the context of a principle serves to include or exclude a certain case from that principle. This is the basis of the discussion of the Gemara here and below.
וְאִיבָּעֵית אֵימָא: לְעוֹלָם רַבִּי יוֹסֵי הִיא, וּתְנָא ״אֵיזוֹ זוֹ״ לְמַעוֹטֵי.
And if you wish, say a different answer: Actually, the mishna is in accordance with the opinion of Rabbi Yosei, and it taught the phrase: In which case is this applicable, to exclude cases of betrothal without a transgression other than those listed in the mishna. The offspring follows the lineage of the father only in those cases specified by the mishna.
״וְאֵיזוֹ זוֹ״ וְתוּ לָא? וַהֲרֵי חָלָל שֶׁנָּשָׂא בַּת יִשְׂרָאֵל, דְּיֵשׁ קִידּוּשִׁין וְאֵין עֲבֵירָה – הַוָּלָד הוֹלֵךְ אַחַר הַזָּכָר! הָא לָא קַשְׁיָא, כְּרַבִּי דּוֹסְתַּאי בֶּן רַבִּי יְהוּדָה סְבִירָא לֵיהּ.
The Gemara asks: But does the list that follows the phrase: In which case is this applicable, include all applicable cases? And are there no more? But there is the example of a ḥalal who married an Israelite woman, where there is betrothal and there is no transgression, and yet the offspring follows the male, as he too is a ḥalal. The Gemara rejects this claim: This is not difficult, as one can say that the tanna of the mishna holds in accordance with the opinion of Rabbi Dostai ben Rabbi Yehuda, who maintains that the offspring of this union is entirely fit.
וַהֲרֵי יִשְׂרָאֵל שֶׁנָּשָׂא חֲלָלָה, דְּיֵשׁ קִידּוּשִׁין וְאֵין עֲבֵירָה – הַוָּלָד הוֹלֵךְ אַחַר הַזָּכָר! תְּנָא ״כׇּל מָקוֹם״ דְּרֵישָׁא, לְאֵתוֹיֵי.
The Gemara asks: But there is the case of an Israelite who married a ḥalala, where there is betrothal and there is no transgression, and the offspring follows the male, and yet this case is not mentioned in the mishna. The Gemara responds: The mishna taught the principle: Any case where there is betrothal and no transgression, in the first clause, to include this situation.
וְנִיתְנְיַיהּ בְּהֶדְיָא! מִשּׁוּם דְּלָא מִתְּנֵי לֵהּ. הֵיכִי נִיתְנֵי? כֹּהֶנֶת וּלְוִיָּה וְיִשְׂרְאֵלִית וַחֲלָלָה שֶׁנִּשֵּׂאת לְכֹהֵן לֵוִי וְיִשְׂרָאֵל – וַחֲלָלָה לְכֹהֵן מִי חַזְיָא?
The Gemara asks: But let the tanna of the mishna teach explicitly this example of an Israelite who married a ḥalala. The Gemara answers: He did not do so because he cannot teach it, i.e., the tanna cannot mention this halakha in brief as part of the list. The Gemara clarifies its answer: How can the tanna teach it? He cannot state: A daughter of a priest; and a daughter of a Levite; and a daughter of an Israelite; and a ḥalala, who married a priest, a Levite, or an Israelite, as, is a ḥalala fit for a priest? This marriage involves a transgression. Consequently, the sentence of the mishna cannot be constructed so as to include a ḥalala.
וְהָאִיכָּא דְּרַבָּה בַּר בַּר חָנָה, דְּאָמַר רַבָּה בַּר בַּר חָנָה אָמַר רַבִּי יוֹחָנָן: מִצְרִי שֵׁנִי שֶׁנָּשָׂא מִצְרִית רִאשׁוֹנָה – בְּנָהּ שְׁלִישִׁי הָוֵי!
The Gemara asks: But there is also the halakha of Rabba bar bar Ḥana, as Rabba bar bar Ḥana says that Rabbi Yoḥanan says: With regard to a second-generation Egyptian man, i.e., the son of an Egyptian convert, who married a first-generation Egyptian woman, a woman who herself converted, her son is considered a third-generation Egyptian who may marry a Jew of unflawed lineage. This is an example of a betrothal without a transgression where the offspring follows the father.
תְּנָא ״כׇּל מָקוֹם״ דְּרֵישָׁא, לְאֵתוֹיֵי. וּלְרַב דִּימִי דְּאָמַר שֵׁנִי הָוֵי, תְּנָא ״אֵיזוֹ זוֹ״ לְמַעוֹטֵי.
The Gemara answers: The mishna taught the principle: Any case where there is betrothal and no transgression, in the first clause, to include this example. The Gemara adds: And according to the opinion of Rav Dimi, who said that this son is a second-generation Egyptian, the mishna taught: In which case is this applicable, at its beginning, with regard to betrothal that does not involve a transgression, to exclude this case. Rav Dimi maintains that this son may not marry a Jew of unflawed lineage.
וְהָאִיכָּא, דְּכִי אֲתָא רָבִין אָמַר רַבִּי יוֹחָנָן: בָּאוּמּוֹת – הַלֵּךְ אַחַר הַזָּכָר.
The Gemara asks: But there is the following case, which apparently contradicts the principle of the mishna: As when Ravin came from Eretz Yisrael he said that Rabbi Yoḥanan says: With regard to the nations, i.e., if members of two different nations married when they were gentiles, follow the male to determine the status of their child. This is the case whether he is a regular gentile, who may marry a Jew of unflawed lineage as soon as he converts, or whether he is an Ammonite or an Egyptian, who may not marry a Jewish woman of unflawed lineage. In either case the child’s status follows that of the father.
נִתְגַּיְּירוּ, הַלֵּךְ אַחַר הַפָּגוּם שֶׁבִּשְׁנֵיהֶם. תְּנָא ״אֵיזוֹ זוֹ״ לְמַעוֹטֵי.
If these members of two different nations converted, follow the flawed lineage of the two. These converts are permitted to marry one another and their betrothal is effective. If either the father or mother is Egyptian, the child follows the parent with the flawed lineage and would be Egyptian, whereas according to the principle stated in the mishna, one should follow the male. The Gemara answers: The mishna taught: In which case is this applicable, in the first clause, to exclude this case.
הַאי מַאי? אִי אָמְרַתְּ בִּשְׁלָמָא מַתְנִיתִין רַבִּי יְהוּדָה הִיא, ״כׇּל מָקוֹם״ דְּרֵישָׁא – לְאֵתוֹיֵי יִשְׂרָאֵל שֶׁנָּשָׂא חֲלָלָה, וּדְרַבָּה בַּר בַּר חָנָה, ״אֵיזוֹ זוֹ״ – לְמַעוֹטֵי דְּרַב דִּימִי וְרָבִין!
The Gemara returns to an earlier point: What is this claim, that the mishna is in accordance with the opinion of Rabbi Yosei? Granted, if you say that the mishna is in accordance with the opinion of Rabbi Yehuda, one can explain that the phrase: Any case, of the first clause, serves to include an Israelite who married a ḥalala, as the child follows the father in that case too, and also to include the ruling of Rabba bar bar Ḥana that the son of a second-generation Egyptian who married a first-generation Egyptian woman is a third-generation Egyptian. Furthermore, the expression: In which case is this applicable, serves to exclude the ruling of Rav Dimi that her son is a second-generation Egyptian, and the statement of Ravin citing Rabbi Yoḥanan.
״כׇּל מָקוֹם״ דְּסֵיפָא – לְאֵתוֹיֵי גֵּר שֶׁנָּשָׂא מַמְזֶרֶת. אֶלָּא אִי אָמְרַתְּ רַבִּי יוֹסֵי הִיא, ״כׇּל מָקוֹם״ דְּרֵישָׁא – כְּדַאֲמַרַן, ״אֵיזוֹ זוֹ״ – כְּדַאֲמַרַן, אֶלָּא ״כׇּל מָקוֹם״ דְּסֵיפָא לְאֵתוֹיֵי מַאי?
And the phrase: Any case, of the latter clause, which is referring to betrothal with a transgression, serves to include a convert who married a mamzeret. But if you say that the mishna is in accordance with the opinion of Rabbi Yosei, then granted the phrase: Any case where there is betrothal and no transgression, of the first clause, is as we said, i.e., it includes an Israelite who married a ḥalala; and the phrase: In which case is this applicable, is as we said, i.e., to the exclusion of Ravin or Rav Dimi, and the case of a convert who married a mamzeret. But what does the phrase: Any case, of the latter clause, serve to add?
וּלְטַעְמָיךְ, לְרַבִּי יְהוּדָה ״אֵיזוֹ זוֹ״ דְּסֵיפָא לְמָה לִי? אֶלָּא: אַיְּידֵי דִּתְנָא רֵישָׁא ״אֵיזוֹ זוֹ״, תְּנָא סֵיפָא ״אֵיזוֹ זוֹ״. הָכִי נָמֵי אַיְּידֵי דִּתְנָא רֵישָׁא ״כׇּל מָקוֹם״, תְּנָא נָמֵי סֵיפָא ״כׇּל מָקוֹם״.
The Gemara responds: And according to your reasoning, the same question applies to Rabbi Yehuda as well: Why do I need the phrase: In which case is this applicable, of the latter clause? Rather, you must say: Since the mishna taught its first clause using the phrase: In which case is this applicable, it also taught its latter clause using the phrase: In which case is this applicable, merely for the sake of stylistic consistency. So too here, with regard to Rabbi Yosei’s opinion, one can say: Since the mishna taught the first clause with the expression: Any case, it also taught its latter clause with: Any case.
גּוּפָא: כִּי אֲתָא רָבִין, אָמַר רַבִּי יוֹחָנָן: בָּאוּמּוֹת – הַלֵּךְ אַחַר הַזָּכָר. נִתְגַּיְּירוּ – הַלֵּךְ אַחַר הַפָּגוּם שֶׁבִּשְׁנֵיהֶם.
§ The Gemara discusses the aforementioned matter itself: When Ravin came from Eretz Yisrael, he said that Rabbi Yoḥanan says: With regard to the nations, if members of two different nations married when they were gentiles, follow the male to determine the status of their child. If they converted before marriage, follow the flawed lineage of the two.
מַאי ״בָּאוּמּוֹת הַלֵּךְ אַחַר הַזָּכָר״? כִּדְתַנְיָא: מִנַּיִן לְאֶחָד מִן הָאוּמּוֹת שֶׁבָּא עַל הַכְּנַעֲנִית וְהוֹלִיד בֵּן שֶׁאַתָּה רַשַּׁאי לִקְנוֹתוֹ בְּעֶבֶד?
The Gemara analyzes this statement: What is the meaning of: With regard to the nations, follow the male? As it is taught in a baraita: From where is it derived with regard to one member of the nations outside Eretz Yisrael who engaged in intercourse with a Canaanite woman and fathered a son from her, that you are permitted to purchase the son as a slave, and he is not considered a member of the Canaanite nations, who are not allowed to live in Eretz Yisrael?
תַּלְמוּד לוֹמַר: ״וְגַם מִבְּנֵי הַתּוֹשָׁבִים הַגָּרִים עִמָּכֶם מֵהֶם תִּקְנוּ״. יָכוֹל אַף עֶבֶד שֶׁבָּא עַל שִׁפְחָה מִן הָאוּמּוֹת וְהוֹלִיד בֵּן שֶׁאַתָּה רַשַּׁאי לִקְנוֹתוֹ בְּעֶבֶד? תַּלְמוּד לוֹמַר: ״אֲשֶׁר הוֹלִידוּ בְּאַרְצְכֶם״ – מִן הַנּוֹלָדִין בְּאַרְצְכֶם, וְלֹא מִן הַגָּרִים בְּאַרְצְכֶם.
The verse states: “And also of the children of the residents who sojourn with you, of them you may buy” (Leviticus 25:45), which indicates that there is a way in which one may purchase slaves from the inhabitants of Canaan. One might have thought that even with regard to a Canaanite slave who engaged in intercourse with a maidservant from the other nations and fathered a son, that you are permitted to buy the son as a slave. Therefore, the verse states: “Which they have begotten in your land” (Leviticus 25:45). This means that one may purchase from those who are merely begotten in your land, whose fathers are not from the Canaanite nations, but not from those who reside in your land, i.e., whose fathers are from the seven Canaanite nations.
״נִתְגַּיְּירוּ הַלֵּךְ אַחַר הַפָּגוּם שֶׁבִּשְׁנֵיהֶם״ – בְּמַאי? אִילֵימָא בְּמִצְרִי שֶׁנָּשָׂא עַמּוֹנִית, מַאי פָּגוּם אִיכָּא, ״עַמּוֹנִי״ – וְלֹא עַמּוֹנִית!
The Gemara discusses the second clause of Rabbi Yoḥanan’s statement: If they converted, follow the flawed lineage of the two. To which case does this refer? If we say that it is referring to an Egyptian man who married an Ammonite woman, what flawed lineage is there here? The lineage of an Ammonite woman who converts is not flawed at all, as the Sages expounded that the verse: “An Ammonite…shall not enter into the assembly of the Lord” (Deuteronomy 23:4) is referring to an Ammonite man but not an Ammonite woman, which means that she can marry a Jew of unflawed lineage.
אֶלָּא בְּעַמּוֹנִי שֶׁנָּשָׂא מִצְרִית, וְאִי זָכָר הָוֵי – הַאי שִׁדְיֵהּ אַבָּתְרֵיהּ דִּידֵיהּ, וְאִם נְקֵבָה הָוְיָא – שִׁדְיַהּ אַבָּתְרַהּ דִּידַהּ.
Rather, it must be referring to an Ammonite man who married an Egyptian woman, and in that case if the child is a male, cast him after his father, and render him permanently prohibited from entering the congregation as an Ammonite male. And if the child born to them is a female, cast her after the mother, so that she is considered a second-generation Egyptian, who may not marry a Jew of unflawed lineage.
כֹּל שֶׁאֵין לָהּ עָלָיו קִידּוּשִׁין. מְנָא הָנֵי מִילֵּי? דְּאָמַר רַבִּי חִיָּיא בַּר אַבָּא אָמַר רַבִּי יוֹחָנָן וּמָטוּ בָּהּ מִשּׁוּם דְּרַבִּי יַנַּאי, וְרַב אַחָא בְּרֵיהּ דְּרָבָא וּמָטוּ בָּהּ מִשּׁוּם רַבִּי יוֹסֵי הַגְּלִילִי: אָמַר קְרָא: ״וְיָצְאָה מִבֵּיתוֹ וְהָלְכָה וְהָיְתָה לְאִישׁ אַחֵר״ – לַאֲחֵרִים וְלֹא לִקְרוֹבִים.
§ The mishna teaches that in any case where a woman cannot join in betrothal with him, but she can join in betrothal with others, the offspring is a mamzer. The Gemara explains: From where are these matters derived? As Rabbi Ḥiyya bar Abba says that Rabbi Yoḥanan says, and some determined that it was said in the name of Rabbi Yannai; and Rav Aḥa, son of Rava, determined that it was said in the name of Rabbi Yosei HaGelili: The verse states with regard to a divorced woman: “And she departs out of his house, and goes and becomes another man’s wife” (Deuteronomy 24:2). This teaches that she can become the wife of others, but not of relatives, i.e., betrothal to forbidden relatives does not take effect.
מַתְקֵיף לַהּ רַבִּי אַבָּא: וְאֵימָא ״לְאַחֵר״ וְלֹא לְבֵן! בֵּן בְּהֶדְיָא כְּתִיב בֵּיהּ: ״לֹא יִקַּח אִישׁ אֶת אֵשֶׁת אָבִיו״, ״אַחֵר״ לְמָה לִי? שְׁמַע מִינַּהּ לַאֲחֵרִים וְלֹא לִקְרוֹבִים.
Rabbi Abba objects to this: But one can say and explain that the term “another” in the verse indicates: But not to her husband’s son, i.e., betrothal is ineffective only in the case of a prohibition that warrants court-imposed capital punishment, not one that warrants karet. The Gemara rejects this suggestion: With regard to a son it is explicitly written: “A man shall not take his father’s wife” (Deuteronomy 23:1), which means that betrothal is ineffective in this situation. If so, why do I need the emphasis of the term “another”? Learn from this term that she may marry others but not relatives.
וְאֵימָא: אִידֵּי וְאִידֵּי לְבֵן, הָא – לְכַתְּחִילָּה, וְהָא – דִּיעֲבַד.
The Gemara challenges this explanation: But one can say that both this verse and that verse are referring to a son and yet both are necessary, as this verse: “Shall not take,” is referring to the halakha ab initio. It does not mean that betrothal is ineffective, but merely that one may not marry his father’s wife. And that verse: “And becomes another man’s wife,” teaches that even after the fact, if the son attempted to betroth his father’s wife, his act is of no consequence.
לְכַתְּחִילָּה מֵאֲחוֹת אִשָּׁה נָפְקָא: וּמָה אֲחוֹת אִשָּׁה, בְּכָרֵת לָא תָּפְסִי בַּהּ קִידּוּשִׁין, חַיָּיבֵי מִיתוֹת בֵּית דִּין לֹא כׇּל שֶׁכֵּן?
The Gemara responds: One learns that betrothal is ineffective in this case ab initio from a different source, as it is derived from the prohibition proscribing a wife’s sister by the following a fortiori inference: If, with regard to the prohibition proscribing a wife’s sister, whose transgression is punished with karet, she cannot be betrothed by her sister’s husband, in accordance with the verse: “And you shall not take a woman with her sister” (Leviticus 18:18), then with regard to cases that entail liability to receive court-imposed capital punishment, e.g., intercourse with one’s father’s wife, is it not all the more so the case that betrothal does not take effect?
וְאֵימָא: אִידֵּי וְאִידֵּי בַּאֲחוֹת אִשָּׁה, הָא – לְכַתְּחִילָּה, הָא – דִיעֲבַד! אִין הָכִי נָמֵי.
The Gemara suggests another interpretation of the verses. But as the verse has already prohibited betrothal to a wife’s sister, one can say as follows: Both this verse: “You shall not take” (Leviticus 18:18), and that one: “Becomes another man’s wife” (Deuteronomy 24:2), are referring to a wife’s sister, as this one: “You shall not take,” prohibits this relationship ab initio, whereas that verse: “Another man’s wife,” teaches that this betrothal is of no effect even after the fact. The Gemara responds: Yes, it is indeed so. The verse should be interpreted in this manner.
אַשְׁכְּחַן אֲחוֹת אִשָּׁה, שְׁאָר עֲרָיוֹת מְנָלַן? יָלְפִינַן מֵאֲחוֹת אִשָּׁה: מָה אֲחוֹת אִשָּׁה מְיוּחֶדֶת, שֶׁהִיא עֶרְוָה וְחַיָּיבִין עַל זְדוֹנָהּ כָּרֵת וְעַל שִׁגְגָתָהּ חַטָּאת – וְלָא תָּפְסִי בָּהּ קִידּוּשִׁין, אַף כֹּל שֶׁהִיא עֶרְוָה וְחַיָּיבִין עַל זְדוֹנָהּ כָּרֵת וְעַל שִׁגְגָתָהּ חַטָּאת – לָא תָּפְסִי בָּהּ קִידּוּשִׁין.
The Gemara asks: We found a source for the prohibition proscribing a wife’s sister; from where do we derive that betrothal is also ineffective for the other forbidden relations? The Gemara answers: We derive it from the case of a wife’s sister, by means of the following analogy: Just as the prohibition with regard to a wife’s sister, which is specified by the Torah, is a prohibition of a forbidden relative that is punished with karet for its intentional transgression and requires a sin-offering for its unwitting transgression, and betrothal is ineffective in this case, so too, with regard to any prohibition that involves a forbidden relative whose intentional transgression is punished with karet and whose unwitting transgression renders one liable to bring a sin-offering, betrothal is likewise ineffective in those cases.
בִּשְׁלָמָא כּוּלְּהוּ אָתְיָין, אֶלָּא אֵשֶׁת אִישׁ וְאֵשֶׁת אָח – אִיכָּא לְמִיפְרַךְ: מָה לַאֲחוֹת אִשָּׁה, שֶׁכֵּן אֵין לָהּ הֶיתֵּר בִּמְקוֹם מִצְוָה – תֹּאמַר בְּאֵשֶׁת אָח שֶׁיֵּשׁ לָהּ הֶיתֵּר בִּמְקוֹם מִצְוָה.
The Gemara asks: Granted, virtually all other forbidden relatives can be derived in this manner. But the cases of a married woman and a brother’s wife are exceptions, and the analogy in these cases can be refuted as follows. What is unique about a wife’s sister is that she is not permitted in the case of a mitzva, as even where the mitzva of levirate marriage would apply, one still may not marry one’s wife’s sister. Will you say the same with regard to a brother’s wife, who is permitted in the case of the mitzva of levirate marriage?
אֵשֶׁת אִישׁ נָמֵי אִיכָּא לְמִיפְרַךְ: מָה לְהָנָךְ, שֶׁכֵּן אֵין לָהּ הֶיתֵּר בְּחַיֵּי אוֹסְרָן – תֹּאמַר בְּאֵשֶׁת אִישׁ שֶׁיֵּשׁ לָהּ הֶיתֵּר בְּחַיֵּי אוֹסְרָן!
With regard to a married woman the interpretation can likewise be refuted: What is unique about these cases of a wife’s sister and a brother’s wife is that they cannot be permitted during the lives of those whose existence renders them prohibited, as neither a wife’s sister nor a brother’s wife can be permitted while the person who causes the prohibition is alive. This caveat is added because one’s wife’s sister does become permitted once his wife has died. Will you say the same with regard to a married woman, who can become permitted during the life of the one who renders her forbidden, by means of a divorce?
אֶלָּא אָמַר רַבִּי יוֹנָה וְאִיתֵּימָא רַב הוּנָא בְּרֵיהּ דְּרַב יְהוֹשֻׁעַ: אָמַר קְרָא: ״כׇּל אֲשֶׁר יַעֲשֶׂה מִכֹּל הַתּוֹעֵבֹת הָאֵלֶּה וְנִכְרְתוּ״, הוּקְשׁוּ כׇּל הָעֲרָיוֹת כּוּלָּם לַאֲחוֹת אִשָּׁה, מָה אֲחוֹת אִשָּׁה לֹא תָּפְסִי בָּהּ קִידּוּשִׁין – אַף כׇּל עֲרָיוֹת כּוּלָּם לֹא תָּפְסִי בָּהּ קִידּוּשִׁין.
Rather, this halakha, that betrothal is ineffective for other forbidden relatives, is derived from a different source, as Rabbi Yona says, and some say this was taught by Rav Huna, son of Rav Yehoshua: The verse states explicitly in the chapter dealing with forbidden relatives: “Whoever shall do any of these abominations shall be cut off” (Leviticus 18:29). In this verse all those with whom relations are forbidden are juxtaposed to one another, and therefore also to a wife’s sister: Just as betrothal is not effective in the case of a wife’s sister, so too, betrothal is not effective with regard to all those with whom relations are forbidden.
אִי הָכִי,
The Gemara asks: If so, that this halakha is derived from here,
