The Secret of Intercalation

"Intercalation of the month with three. Intercalation of the year with three"—the words of Rabbi Meir. Rabban Shimon ben Gamliel says: "We begin with three, with five we argue back and forth, and with seven we finish. But if you finish with three, then it has been intercalated."

(1) A leap year is a year in which another month has been added. And we only ever add an Adar and make two Adars, an Adar Rishon (first Adar) and an Adar Sheini (Second Adar). And why do we add this month? Because of the spring time, so that the Passover will fall at that time, as it is said (Deuteronomy 16:1) "Guard the month of the spring", that this month should be in the spring. And if it wasn't for the addition of this month, Passover would sometimes come in the days of the sun (the summer) and sometimes in the days of the rain (the winter).

(2) For three indicators we make the year a leap [year]. For the epoch and for the spring and for the fruit of the trees. How? The court calculates and knows; if the epoch of Nissan (when the sun enters Aries) will be on the 16th of Nissan or after this time, they make the year into a leap [year]. And they make that Nissan an Adar Sheini in order that the Passover will be in the spring time. And on this indicator, we rely and make leap [years] and we are not concerned about another indicator.

(3) And similarly, if the court saw that the spring has yet to arrive, rather it is still dark. And the fruit of the trees that tend to sprout around Passover have not sprouted. We rely on these two indicators and make the year a leap [year]. So that the spring will be present to offer up from it the waved omer (an offering of grain) on the 16th of Nissan. And in order that the fruit will sprout normally throughout the spring time.

(4) And we rely on three lands with respect to the spring. On the land of Yehuda and on the Jordan Bank and in the Galil. And if the spring arrived in two of these lands and in one it didn't, we don't make it a leap [year]. And if it arrived in one of them and it didn't arrive in two, we make it a leap [year], if the fruit of the trees is yet to sprout. And these are the main things that we make leap [years] for in order that the years will be solar years.

(5) And there exist other things that the court makes leap [years] for due to necessity. And these are they: Because of the roads that are not mended and the people are unable to go up [to Jerusalem], we make the year a leap [year] until the rain stops and the roads are mended. And because of the bridges which were demolished and the rivers are found blocking and preventing the people or they are endangering themselves and dying, we make the year a leap [year] until they mend the bridges. And because of the passover ovens that were destroyed in the rain and they don't have place to roast their passover [offerings], we make the year a leap [year] until they will have built the ovens and they will have dried. And because of the Israelite exiles that have been uprooted from their place and are yet to have arrived in Jerusalem, we make the year a leap [year] in order that they will have enough time to arrive.

(8) Rabban Gamliel had, on a tablet, and on the walls of his loft, various drawings of the moon, which he showed to simple witnesses, and said, "Was it like this [drawing] that you saw, or like [the other one]?" It happened once, that two witnesses came and said, "We saw [the moon] in the East in the morning, and in the evening in the West." [In that case,] Rabbi Yochanan ben Nuri said, "They are false witnesses." [But] when they came to Yavneh, Rabban Gamliel accepted [their testimony. It] also [happened once that] two witnesses came and said, "We saw the moon at its time [meaning, on the first of the two possible days], but it was not [to be] seen [afterwards] on the evening of its intercalation," and Rabban Gamliel accepted [their testimony]. Rabbi Dosa ben Harkinus said, "They are false witnesses; how can they testify that a [certain] woman gave birth [on a certain day], and, on the next day that her 'womb was between her teeth' [and the fetus still inside]?" [Then] Rabbi Yehoshua said to him, "I perceive [the truth of] your words."

(9) [Upon hearing this,] Rabban Gamliel sent [Rabbi Yehoshua] word, saving, "I decree upon you to come to me with your staff and your money on the day that comes out to be Yom Kippur, according to your calculation." Rabbi Akiva went to [Rabbi Yehoshua], and found him grieving; he said to him, "I have with what to teach, that all that Rabban Gamliel has done is [bindingly] done, as it is stated (Leveticus 23:4), 'These are the feasts of the Lord, holy convocations which you shall proclaim;' whether at their [proper] time, or whether not at their [proper] time, I have no holy convocations except [for the ones proclaimed by the court." When Rabbi Yehoshua] came to Rabbi Dosa ben Harkinus, [the latter] said to him, "If we are to [question the decisions] of the court of Rabban Gamliel, we must [also question the decisions] of all the courts which have stood, from the days of Moshe until [today]; as it is stated, (Exodus 24:2), 'Moshe, Aharon, Nadav, Avihu, and seventy of the elders of Israel went up.' Why were the names of the elders not specified? Rather [it was] to teach, that every three men that form ‏a court [to be responsible] over Israel, behold [that court] is to be [considered] like the court of Moshe." [After this], Rabbi Yehoshua took his staff and his money in his hand, and went to Yavneh to Rabban Gamliel on the day that came out to be Yom Kippur, according to his calculation. [At that point], Rabban Gamliel stood up, and kissed him on his head, [and] he said to him, "Come in peace, my teacher and my disciple! My teacher — in wisdom; and my disciple — in that you accepted my words."