Keritot, Chapter Three, Mishnah Seven
In our mishnah Rabbi Akiva begins to ask concerning the question of how one distinguishes between separate transgressions, for which one is liable for each individually, and one extended transgression, for which one is liable only once.
1) Rabbi Akiva said: I asked Rabban Gamaliel and Rabbi Joshua at the meat-market of Emmaus, where they went to buy meat for the wedding feast of Rabban Gamaliel’s son:
2) What [is the law concerning] a man who had intercourse with his sister, his father’s sister and his mother’s sister? Is he liable for one sacrifice for all of them, or to one [separate sacrifice] for each of them?
3) They replied: we have heard nothing [about this], but we have heard that if one had intercourse with five menstruants in one spell of unawareness, he is liable to a sacrifice for each [act], and it seems to us that the case [you asked about] may be derived by an a fortiori conclusion (kal vehomer).
Section one: The mishnah begins with an interesting tidbit of historical information. Rabbi Akiva was in Emmaus (near the Latrun exit on the Tel-Aviv-Jerusalem highway, not far from my house). There he ran into Rabban Gamaliel and Rabbi Joshua buying meat for Rabban Gamaliels sons wedding. Feeling himself lucky to run into some rabbis, probably not an everyday occurrence, he decides to ask them a halakhic riddle. Note that the question is not a practical one, but rather an academic one. This is an interesting window into what kinds of questions rabbis asked each other when they met.
Section two: The case is one in which a man had relations with three women prohibited to him, all of whom are different types of prohibited sisters. All three transgressions were done in one period of unawareness. Either he didnt know that there was such a prohibition, or he didnt know that these women were his sister, fathers sister and mothers sister. Thus the question is, if in one period of unawareness one commits three transgressions that are called by a similar name, is he liable for three hatats or one?
Section three: Rabban Gamaliel and Rabbi Joshua respond that they dont have an answer to the question, at least not one that they have received from their teachers. In other words, Rabbi Akiva has thought of a new situation that was never before discussed. [Good job, Rabbi Akiva!] While they dont have a received answer, they do have a similar received tradition concerning a man who has relations with five menstruants in one period of unawareness. Despite the fact that this is one type of transgression (prohibition of sex with a menstruant) he is liable for a hatat for each transgression. It seems that he is liable for five hatats because each one is a different woman. The distinctness of their bodies one from the other makes these five sins and not one sin of transgressing the prohibition of sex with a menstruant. From this case Rabban Gamaliel and Rabbi Joshua conclude that all the more so (kal vehomer) in the case of the three sisters, he would be liable for a hatat for each sister, because there is some difference between the status of each sisterwhile they are all sisters they are different types of sisters.