Yesterday, the rabbis discussed the specifics of an eruv techumin in a case where a festival falls adjacent to Shabbat. Much of that discussion turned on the question of whether both days are considered a single sacred event or not.
Today, the rabbis discuss a similar question with respect to the two days of Rosh Hashanah. Are they two sacred events or one? The answer to that question has direct bearing on whether one can establish a single eruv for all of Rosh Hashanah or whether a separate eruv is needed for each potential day.
Wait — potential day? Isn’t Rosh Hashanah always two days?
It has been for a long time, but that wasn’t always the case.
Before the advent of a fixed calendar, the start of each month was determined by the testimony of two witnesses who saw the new moon in the sky, indicating a new month had begun. If witnesses arrived on the 30th day of a month and declared they had seen the moon the previous night, that day would be declared the first day of the new month. But if they didn’t appear on the 30th, the following day would be declared the first day of the new month.
As a result, Rosh Hashanah could be observed for one day in some years and for two days in others. Rosh Hashanah would always be observed on the 30th day of the month of Elul. If witnesses arrived on that day, it would be declared to actually be the first day of the following month, Tishrei, and Rosh Hashanah would be only one day that year. But if they didn’t arrive on the 30th, Rosh Hashanah would be extended into the following day, which would then be the first of Tishrei.
Given this, the mishnah teaches this law:
Rabbi Yehuda says: With regard to Rosh Hashanah, if one feared that the month of Elul might be extended, this person may establish two eruvin and say: My eruv on the first day shall be to the east and on the second day to the west, or alternatively: On the first day it shall be to the west, and on the second day to the east. Similarly, he may say: My eruv shall apply on the first day, but on the second day I shall be like the rest of the inhabitants of my town, or alternatively: My eruv shall apply on the second day, but on the first day I shall be like the rest of the inhabitants of my town. And the rabbis did not agree with him that the two days of Rosh Hashanah can be divided in such a manner.
The mishnah is discussing the concept of a conditional eruv, of the sort we first encountered in Eruvin 36. If Rosh Hashanah is two days in a given year, Rabbi Yehuda says you can place an eruv in two locations and decide that one is operative on one day and the other on the second day. But the majority do not accept this, ruling that one may not separate the days of Rosh Hashanah in this manner, as they are one continuously sacred event.
The Gemara tells us that the case in the mishnah is one in which witnesses arrive on the 30th day of Elul, but after the time for testifying has passed. In this instance, everyone agrees that their testimony is invalid and Rosh Hashanah is observed for another day. The disagreement is over whether a conditional eruv could be established in such a case.
One opinion holds that the extension of Rosh Hashanah into an additional day that we know to be a weekday (because the witness testimony is accurate, even though it is ignored) is evidence that both days are a single sacred event. Therefore, it is forbidden to establish a separate eruv for each day.
The other holds that the sanctification of the 30th day of Elul is done to protect the sanctity of Rosh Hashanah in a year when it is observed for just one day. Given the yearly fluctuations, people might come to violate the first day, expecting there to be a second one that is truly the holiday. But this assumption might lead to a desecration of the holiday when it actually falls on the first day. To avoid that, the first day is sanctified even when it is simply the 30th of Elul, suggesting that the sanctity of the first day is distinct from the second and that multiple eruvim should be allowed.
The Gemara does not reach a clear conclusion on this question. We’ll take a deep dive into these matters when we get to Tractate Rosh Hashanah in about a year. Stay tuned.
Read all of Eruvin 39 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on September 17, 2020. If you are interested in receiving the newsletter, sign up here.
