The year 5752 Anno Mundi (1991-1992) was a leap-year in the Jewish calendar, adding a whole month to the usual twelve. This occurs with a certain regularity in a cycle of 19 years. The 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years are leap-years; the others are 12-month years. This arrangement brings the 354 days of the lunar year (12 x 29 1/2) in line with the 365 days of the solar year, assuring that the Festival of Passover occurs in the beginning of the Spring season. The occurrence of a leap-year has led to a number of problems concerning the observance of the various holidays and other rituals, as discussed in Talmudic and post-Talmudic literature. Actually, the more serious problems arose during the period in Jewish history prior to the middle of the fourth century, C.E., when Hillel the 2nd fixed the calendar that is in use today. In that period, the beginning of each month (Rosh Hodesh) had to be determined and declared by the High Court in Israel, which was also charged with the responsibility of deciding every year whether or not it should be proclaimed as a leap-year.
Let us examine one of the major problems faced by the Jewish people in those days as a consequence of this ad hoc fixing of the calendar, bearing in mind that the Jewish reckoning of the annual cycle of months begins with the month of Nisan, which must, necessarily, occur after the Spring equinox (Exodus 12:2, 13:4). The Mishnah (Eduyot 7:7) records that Rabbis Yehoshua and Papias testified (before the Sages in Yavneh) that a leap-year could be decided upon as late as the 29th day of Adar (the month before Nisan), whereas previously it had been ruled that it has to be decided upon before Purim (which is celebrated on the 14th of Adar). The Talmud (B. Rosh Hashanah 7a) explains the previous ruling as follows: Already at Purim time, 30 days before Passover, public discussions were conducted concerning the laws of Passover and, thus, the people anticipated that festival to occur within a month. If an additional month were to be proclaimed after Purim, there would be much confusion concerning Passover, as people would refuse to believe the messengers reporting the postponement of Passover. The earlier ruling seems reasonable enough, but the Talmud offers no reason why the authorities in Yavneh decided to change the rule. It seems to me that the change came about because of a change in historical circumstances. From several statements in the Mishnah (Rosh Hashanah, chap. 2) we know that, in the earlier period, going back to the days of the Second Temple, attempts were made by the Boethusians - a Jewish sect opposed to the rulings of the Sages, then known as the Perushim (Pharisees) - to confuse the people by giving false signals proclaiming the declaration of a new month. This led to circumspection by the people as to the credibility of the messengers of the Court. After the destruction of the Temple, the Boethusians ceased to exist as an active group and, thus, there no longer existed any fear that the messengers might be false.
Be this explanation as it may, it is clear that the ruling that an additional month may be added even after Purim created a serious problem. For example: The 14th day of Adar arrived and the people observed the holiday of Purim; they read the Megillah; they sent manot (edible portions) to friends and gifts to the poor. And, behold, a week later the High Court decided to add another month, a second Adar, to the year. Immediately the question arose: Will we have to celebrate Purim again when the 14th day of the second Adar arrives? The Mishnah gives a clear answer: it has to be read again in Adar Two (B. Megillah 6b). The Talmud explains: "To bring one redemption (ge'ulah) close to another," i.e., to bring close together the celebration of Israel's redemption from the evil decree of Haman and the celebration of Israel's redemption from bondage in Egypt.
An examination of other Talmudic sources related to this problem reveals that it had not been completely resolved by the Sages of Yavneh. …