We arrive at Mishnah 7 in the third chapter of Tractate Kesubos, and with it, we conclude the topic we have been discussing in the recent mishnayos: cases where a person performs a single act, and by virtue of that very act, he becomes liable for multiple sin-offerings. Our Mishnah seeks to clarify the root of this law - where it is derived from and what its source is.
Background to the Mishnah's words:
The Mishnah opens: "Amar Rabbi Akiva: Sha'alti es Rabban Gamliel v'es Rabbi Yehoshua b'itliz shel Ema'um, shehalchu likach behemah l'mishteh bno shel Rabban Gamliel" - Rabbi Akiva said: I asked Rabban Gamliel and Rabbi Yehoshua in the meat market of Ema'um, when they went to buy an animal for the feast of Rabban Gamliel's son. Rabbi Akiva relates that he was in the meat market in a place called Ema'um together with Rabban Gamliel the Nasi and Rabbi Yehoshua, his teacher and the Torah leader of the generation, who came there to buy an animal for the feast of Rabban Gamliel's son. Even though it is not strictly necessary to detail why this background is mentioned, it seems to teach us how dedicated the Sages were to delving into the depths of halachah and expanding the Oral Torah, even while they were busy shopping for a feast.
Rabbi Akiva's question is: "Haba al achoso, v'al achos aviv, v'al achos imo b'helam echad, mahu?" - If one has relations with his sister, his father's sister, and his mother's sister in a single lapse of awareness, what is the law? We have before us another case, different from the previous ones but fundamentally similar: a person who has relations with a woman who is forbidden to him from several different angles, where it is a single act that involves multiple prohibitions.
Two possibilities stand before him:
"Chayav achas al kulan" - is he liable for one on all of them? Since only a single act was performed, even though it involves three Torah prohibitions, he brings only one sin-offering.
"O achas al kol achas v'achas" - or one for each and every one? He brings a sin-offering for each of the different categories, meaning for each of the sins and commandments of the 613 that he transgressed in this single act.
"Amru lo: Lo shamanu" - they said to him: We have not heard. Rabban Gamliel and Rabbi Yehoshua replied that they did not have a tradition with which to answer this question.
Constructing the case:
This involves an unusual case, as is typical of the cases taught here. Leah gave birth to a son named Reuven. From Leah and Reuven, two daughters were born, Dinah and Rachel. Reuven fathered a son with his daughter Dinah, and this is Chanoch. It emerges that Chanoch is forbidden to Rachel in three ways:
His sister: Chanoch and Rachel share one father - Reuven.
His father's sister: Chanoch's father is Reuven, and Reuven and Rachel share one mother - Leah, so Rachel is Reuven's sister.
His mother's sister: Chanoch's mother is Dinah, and Dinah and Rachel are sisters from both parents, Reuven and Leah.
The question is, therefore, if Chanoch has relations with Rachel - is he liable for one sin-offering or three sin-offerings? It is worth noting that this same question applies equally to Rachel. It should be pointed out that it is not strictly necessary to analyze the details of the family tree so closely, since they neither add nor detract from the essence of the discussion, and any of the examples taught in the previous mishnayos could have been brought for this same question.
"Aval shamanu" - but we have heard:
Although the Sages did not have a tradition on this specific point, they did have another tradition: "Habba al chamesh nashav niddos behe'elam echad" - A man who had relations with five of his wives, and each one of them was a niddah, in a single lapse of awareness, meaning out of a single forgetting of the law. His wives are permitted to him, and there is only the prohibition of niddah here. Since he violated this same prohibition five times, the law is that he is liable for each and every one, and he brings a chatas for each and every act - five wives, five acts, and five chatas offerings, even though there was one lapse of awareness, and even though there is only one category here, the prohibition of niddah, one of the 613 mitzvahs.
"Vera'inu es hadevarim kal vachomer" - From here, Rabban Gamliel and Rabbi Yehoshua reasoned through a kal vachomer: If in a single lapse of awareness, when a person violates one prohibition five times, he is liable for five chatas offerings, kal vachomer that when in a single lapse of awareness he violates five prohibitions, even though it involves one person, he should be liable for five chatas offerings. This implies that they did not view the fact that the wives are separate entities as the deciding factor, but rather focused solely on the number of transgressions: one prohibition of niddah in one lapse of awareness compared to five, and opposite it, the case of Rabbi Akiva - three transgressions in one act.
However, the Gemara does not accept this kal vachomer, because it treats the matter of separate entities - different women, different bodies - as a separate and important factor, and possibly no less important than the number of mitzvahs transgressed. Therefore, one cannot necessarily extrapolate through a kal vachomer to a situation involving only one woman and three prohibitions.
The source from the verse:
Therefore, the Gemara concludes that the source for this rule, which applies to all the latter cases of the Mishnah, is a derivation from the verses dealing with the prohibition of one who has relations with his sister. First it states: "And a man who takes his sister, the daughter of his father or the daughter of his mother... they shall be cut off in the sight of the children of their people" - thus the verse lists the two possibilities of a sister, a sister from the father and a sister from the mother, and consequently even a sister from both, and one who has relations with her incurs kares.
The subsequent verse continues: "He has uncovered his sister's nakedness, he shall bear his iniquity." Seemingly, this has already been stated, so what does it come to add? Rather, it comes to teach that a person can be liable for both aspects: when the woman is forbidden to him from two different angles, such as his sister from his father and his sister from his mother, he is liable twice, based on two separate verses, two separate transgressions, and two different categories and prohibitions out of the 613 mitzvahs.
In summary: Based on this derivation, and not based on the kal vachomer, it is learned that a person incurs several chatas offerings for one woman when it involves two separate mitzvahs from the Torah. This law is extended to every scenario where one act involves several prohibitions, and in which a person is liable for several chatas offerings for one act. This is how the halachah is ruled in practice.