As we learned on yesterday’s daf, Rabbi Shimon ben Azzai reported that he found a scroll in Jerusalem that accused King Menashe of having killed the prophet Yeshayahu. Rava comments that Menashe did not simply murder him, but rather he put him on trial for heresies that appear among his prophecies. Although Yeshayahu could explain each one of them, he chose not to do so because he knew that Menashe would kill him in any case and he preferred that Menashe not be held responsible for murder.
One of the supposed heresies was the following: The Torah says that every person lives out his appointed days (see Shemot 23:26), yet Yeshayahu told King Hizkiyahu that he would have 15 years added to his life (see II Melakhim 20:6). The Gemara on our daf explains that there is a disagreement between Rabbi Akiva and the Hakhamim about how to define living out one’s days. Everyone has a designated amount of years, which are referred to as shnei dorot – the years set aside for a person to live in his generation. According to Rabbi Akiva, if he is deserving, he will live out his time; if he does not merit it, however, years may be subtracted from his life. The Hakhamim believe that a person’s merit can either add or subtract from the time that is set for him.
The Tosefot HaRosh explains that the term shnei dorot is used because God establishes the years of the entire generation, rather than each individual person (see Yeshayahu 41:4). The ge’onim offer a different explanation, arguing that shnei dorot refers to the length of time that a person would ordinarily be expected to live, given his health and physical make-up. The Rambam wrote a lengthy treatise in Arabic which offers a synopsis of the different positions on this matter from the perspectives of scholarship and medicine.