This Month Shall Be the First of Months for Israel

"This month is for you" (Exodus 12:2): the early fathers did not count by it. Might one think the early fathers did not count by it because the Torah had not been given in their days, but from the time the Torah was given onward all who came into the world would count by it? Scripture says "for you": you count by it, and those who came into the world do not count by it. "The head of months": Might one think also for years and for sabbatical cycles and for jubilees? Scripture says "the head of months": it is the head for months, but it is not the head for years, nor for sabbatical cycles, nor for jubilees. "It is the first for you": and not for the tithe of cattle, nor for produce. For what is it first? For kings, and for festivals, and for the contribution of shekels, and for the renting of houses. "It is the first": from the fact that it is said, "Observe the month of Abib" (Deuteronomy 16:1)—how do you observe it? You add days to it [by intercalation]. Might one think that if the year was short by ten days or twenty days he should let it pass thus? Scripture says "a month": no less than a month [is added]. Might one think that if the year was short by forty days or fifty days he should let it pass thus? Scripture says "a month": no more than a month. Might one think he should intercalate Nisan? Scripture says "it is the first for you": you make one Nisan, and you do not make a second Nisan. Might one think he should intercalate Tishrei? Scripture says "Observe the month of Abib": observe the month adjacent to the spring, and which is that? Adar. Might one think that just as if the year was late he adds days to it, so too if the year was early he should subtract days from it? Scripture says, "And you shall keep this ordinance in its season from days to days" (Exodus 13:10): no less than twelve months. "It is the first for you for the months of the year": that he not make a second Nisan.