Study Yevamot folio 55A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
Text Excerpt
אלמא אחות אשתו, בין מן האב בין מן האם — אסורות. מנלן? יליף מאחותו. מה אחותו — בין מן האב בין מן האם, אף כאן — בין מן האב בין מן האם.
Apparently, this Mishnah indicates that his wife’s sister, whether from the father, i.e., a paternal sister, or from the mother, i.e., a maternal sister, is forbidden. From where do we derive this halakha that the prohibition applies even to his wife’s maternal sister? The Talmud responds: It is derived from the prohibition proscribing his sister. Just as his sister is forbidden whether she is his sister from his father or from his mother, so too here, a wife’s sister is forbidden whether from the father or from the mother.
ולילף מדודתו: מה דודתו מן האב ולא מן האם, אף כאן מן האב ולא מן האם! מסתברא מאחותו הוה ליה למילף, שכן קרובי עצמו מקרובי עצמו.
The Talmud challenges the validity of this source: And let it be derived from the halakha with regard to his aunt: Just as the prohibition with regard to his aunt applies only to the wife of his father’s brother from his father but not from his mother, i.e., the wife of his father’s paternal brother but not the wife of his father’s maternal brother, so too here, the prohibition with regard to his wife’s sister should apply only to her sister from her father but not to her sister from her mother. The Talmud answers: It is reasonable that he should derive the halakha in this case from the case of his sister, as the tanna thereby derives the halakha of one’s own relatives from another case of his own relatives, whereas his aunt is forbidden as his father’s relative.
אדרבה מדודתו הוה ליה למילף, שכן דבר על ידי קדושין מדבר שעל ידי קדושין. אלא מאשת אח ילפינן, דשכן דבר על ידי קדושין, וקרובי עצמו.
The Talmud counters: On the contrary, he should derive the halakha in this instance from the case of his aunt, as he thereby derives the halakha in a matter prohibited through betrothal from another matter prohibited through betrothal. The Talmud concludes: Rather, the halakha of a wife’s sister is derived from that of a brother’s wife, as they are both something forbidden by means of betrothal and they are his own relatives.