The opening Mishna in Massekhet Rosh HaShana teaches that the halakha recognizes four separate dates as being new years, with each one defining the beginning of a new cycle for that particular idea or event. The four new years are:
- The first day of Nissan, which begins the new year for kings and holidays
- The first day of Elul, which begins the new year for tithes taken from flocks of animals
- The first day of Tishrei, which begins the new year for counting years, including shemita (the Sabbatical year) and yovel (the Jubilee year), as well as planting trees and tithes on vegetables
- The first (according to Beit Shammai according to Beit Hillel it is the 15th) of Shevat, which begins the new year for tithes on fruit.
The Gemara will go on to explain each of these items individually. On our daf the focus is on the first day of Nissan, which is the new year for kings. Given the fact that monarchs usually had lifetime positions, why was there a need to establish a particular calendar day that was the beginning of his reign? Theoretically, a king’s reign should begin whenever he took office. Rav Hisda explains that “for kings” means for dating contracts. It was common practice under a given monarchy that the year that would appear in a contract was not the number of years since creation or from an arbitrary point in history, but how many years into the current king’s reign. Rashi explains that this was done for reasons of shalom malkhut— to stay on good terms with the king by honoring him in every matter. Tosafot point out that since the Mishna refers only to Jewish kings (some say that the Mishna’s use of the plural “kings” is to indicate that both kings of Judea and kings of the northern kingdom of Israel were included), shalom malkhut should not apply. They argue that this was simply the common method of dating contracts at that time.
The Mordekhai and the Ge’onim point out that these days become minor holidays, given their description by the Mishna as Rosh HaShana. Therefore a day like the 15th of Shevat becomes a day of celebration to the extent that neither fasting nor eulogies are permitted.