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Text Excerpt
אחות אשה, דבמזיד לא אסירא מדאורייתא, בשוגג לא גזרו בה רבנן. ומנלן דלא אסירא, דתניא: ״אותה״, אותה — שכיבתה אוסרתה, ואין שכיבת אחותה אוסרתה.
However, with regard to a wife’s sister, where even if the sister sins intentionally the wife is not forbidden to him by Torah law, if he did so unwittingly the rabbis did not decree with regard to him. And from where do we derive that she is not forbidden? As it is taught in a baraita that in the verse: “A man, when his wife goes aside…and a man lies with her” (Numbers 5:12–13), the emphasis of “her” teaches: It is her sex with another man that renders her forbidden to her husband, but the sex of her sister does not render her forbidden.
שיכול, והלא דין הוא: ומה במקום שבא על איסור קל — נאסר האוסר, מקום שבא על איסור חמור — אינו דין שנאסר האוסר.
As, were it not for this verse, one might have thought: Could this not be derived through an a fortiori inference: And if in a case where he has sex subject to a light prohibition, the one causing her to be rendered prohibited is forbidden, then in a situation where he has sex subject to a severe prohibition, is it not right that the one causing her to be rendered prohibited should be forbidden? This a fortiori inference will be explained later in the Talmud.
אמר רבי יהודה: לא נחלקו בית שמאי ובית הלל בבא על חמותו שפסל את אשתו, על מה נחלקו — בבא על אחות אשתו, שבית שמאי אומרים: פסל, ובית הלל אומרים: לא פסל. אמר רבי יוסי: לא נחלקו בית שמאי ובית הלל בבא על אחות אשתו שלא פסל את אשתו, על מה נחלקו — בבא על חמותו, שבית שמאי אומרים: פסל, ובית הלל אומרים: לא פסל.
R' Yehuda said: Beit Shammai and Beit Hillel did not disagree with regard to one who has sex with his mother-in-law, that he renders his wife disqualified from remaining married to him. With regard to what case did they disagree? With regard to one who has sex with his wife’s sister, as Beit Shammai say that he renders his wife disqualified, and Beit Hillel say he does not render her disqualified. R' Yosei said: Not so, as Beit Shammai and Beit Hillel did not disagree with regard to one who has sex with his wife’s sister, that he does not render his wife disqualified from remaining married to him. With regard to what did they disagree? With regard to one who has sex with his mother-in-law, as Beit Shammai say he renders his wife disqualified and Beit Hillel say he does not render her disqualified.