Halachah 1 – Only an Authorized Court in Eretz Yisrael Can Sanctify the Months
All procedures involving sanctifying the new month through witnesses and declaring leap years may be performed only by the Sanhedrin in Eretz Yisrael or by courts authorized by them. This authority was transmitted from Moshe Rabbeinu and is derived from the verse, “This month shall be for you.”
Halachah 2 – What Happens When There Is No Sanhedrin
When there is no Sanhedrin in Eretz Yisrael, months and leap years are no longer determined through witness testimony. Instead, the Jewish people rely upon the fixed calendar calculations that are used today.
Halachah 3 – The Fixed Calendar Is a Sinaitic Tradition
The use of witness testimony when a Sanhedrin exists and the use of a fixed calendar when no Sanhedrin exists are both part of a tradition going back to Moshe at Sinai. The modern calendar is therefore not merely a practical replacement, but part of the original halachic system.
Halachah 4 – When the Fixed Calendar Began
The Jewish people began relying entirely on the fixed calendar after the decline of the Talmudic academies and the destruction of organized Jewish authority in Eretz Yisrael. Until the era of Abaye and Rava, Jews throughout the world still relied on the calendar established in Eretz Yisrael.
Halachah 5 – Festival Observance During the Era of Witness Testimony
When the Sanhedrin sanctified months based on witnesses, Jews living in Eretz Yisrael and in places reached by the messengers from Eretz Yisrael observed one day of Yom Tov. Distant communities that could not receive the announcements in time observed two days because of uncertainty.
Halachah 6 – Why Two Days of Yom Tov Continue Today
Technically, once the fixed calendar was established, everyone could calculate the festivals accurately and observe only one day. Nevertheless, the Sages required communities outside Eretz Yisrael to continue following the ancestral custom of observing two days of Yom Tov.
Halachah 7 – The Difference Between Eretz Yisrael and the Diaspora
Communities that historically could not be reached by the Tishrei messengers continue to observe two days of Yom Tov. The inhabitants of Eretz Yisrael continue observing one day because they never adopted two-day observances.
Halachah 8 – Yom Tov Sheni Is Rabbinic
The second festival day observed outside Eretz Yisrael is entirely Rabbinic in nature. It exists because of the enactment of the Sages and the obligation to preserve long-established Jewish practice.
Halachah 9 – Why Rosh Hashanah Was Originally Two Days
Even during the era of witness testimony, most communities in Eretz Yisrael observed two days of Rosh Hashanah. Because witnesses might arrive late, people often could not know with certainty which day had been sanctified by the court.
Halachah 10 – Why Even Jerusalem Sometimes Observed Two Days
Even Jerusalem occasionally observed two days of Rosh Hashanah when witnesses failed to arrive on the first day. Since this two-day observance already existed during the period of sanctification through witnesses, the Sages required both Eretz Yisrael and the Diaspora to continue observing two days of Rosh Hashanah even under the fixed calendar.
Halachah 11 – One Day or Two Days Depends on Historical Practice
Whether a location observes one or two days of Yom Tov does not depend merely on its distance from Jerusalem. A place might be geographically close yet still observe two days because messengers never reached it regularly for historical reasons.
Halachah 12 – Proximity Alone Is Not the Determining Factor
The Rambam proves that distance is not the key factor by pointing out that places such as Egypt and much of Syria could theoretically have been reached by messengers. Nevertheless, many of those places maintained the observance of two days. The determining factor is historical reality, not geography alone.
Halachah 13 – The General Rule for Present-Day Observance
Places located more than ten days from Jerusalem continue their historic practice of observing two days. Places within ten days of Jerusalem that were part of the settled Jewish communities of Eretz Yisrael during the era of the Second Temple observe one day. Other places follow their inherited communal custom, whether one day or two.
Halachah 14 – New Communities Without an Established Tradition
A newly established community in Syria or outside Eretz Yisrael that has no established custom follows the practice of the majority of the Jewish world and observes two days of Yom Tov. This includes the second day of Rosh Hashanah.
Halachah 15 – Why We Calculate the Calendar Today
When Jews today calculate the calendar and determine the dates of Rosh Chodesh and the festivals, they are not establishing the calendar themselves. Rather, they are identifying the dates established through the authority of Eretz Yisrael and the fixed calendar tradition that originated there. The sanctity of the festivals comes from that authority, not from each person’s individual calculations.