There are many arguments for calendar reform, one of which argues that we should set up the calendar so that every date always falls on the same day (Invariable Calendar) .

If this Invariable Calendar were adopted, then the day that we celebrate as Shabbos now, would not necessarily be a Saturday. In fact, if I understand what they are proposing, then the days that would be Saturdays under our current calendar will move around from year to year and maybe from week to week.

Although I doubt such a reform would ever be adopted, I'm curious what we would do halachically if it were. Would we change the date of Shabbos so that it still always fell on the date that was designated Saturday in the calendar, or would we have to figure out a way to keep Shabbos on the date that would be Shabbos in the current system? (The former might be impossible, because the Invariable Calendar adds a day once a year that has no day of the week. So, if we switched Shabbos to every Saturday in the new system, then at least once a year there would be 8 days between Shabboses.)

The answer to this question depends, I know, on how one rules on this question: [History of Shabbat: how (or) did they count to align with 7th day of creation?

  • 3
    Did the adoption of the Gregorian calendar prompt Passover to always be on April 15? Why would this be different?
    – Double AA
    Commented Jul 31, 2018 at 15:52
  • 1
    One wonders how the Jews operated under the French Republican Calendar. My guess is that yom shabbat still followed yom shishi.
    – rosends
    Commented Jul 31, 2018 at 15:59
  • 2
    Related: judaism.stackexchange.com/questions/12760/…
    – Isaac Moses
    Commented Jul 31, 2018 at 16:22
  • @rosends The calendar was used for only 12 years from 1793 to 1805, and was eventually abolished, actually, by religious folk.
    – ezra
    Commented Jul 31, 2018 at 16:35
  • @ezra yes, but during those times, anyone who was following Judaism had to figure out when Shabbat was -- probably by sticking to the same 7 day cycle as always.
    – rosends
    Commented Jul 31, 2018 at 17:37

1 Answer 1


While the Jewish holidays are controlled by the Sanhedrin (though, notably, they are not controlled by non-Jewish governments, and even the Sanhedrin's control is bound by divinely received rules), Sabbath is different in that it always repeats every seventh day, regardless of any calendar. This is one reason given why, in the central prayer of Sabbath/festival/new moons shemoneh esrei, Sabbath is mentioned as directly sanctified by G-d (מקדש השבת), whereas the sanctity of the festivals/new moons is described as corollary to the sanctification of Israel (מקדש ישראל והזמנים).

תני תנא קמיה דרבינא מקדש ישראל והשבת והזמנים אמר ליה אטו שבת ישראל מקדשי ליה והא שבת מקדשא וקיימא אלא אימא מקדש השבת ישראל והזמנים אמר רב יוסף הלכה כרבי וכדתריץ רבינא:

A tanna taught a baraita before Ravina with a slightly different reading: He concludes the blessing with: Who sanctifies the Jewish people, Shabbat, and the seasons. Ravina said to that tanna: Is that to say that the Jewish people sanctify Shabbat? Isn’t Shabbat already sanctified from the six days of Creation? Every seventh day is automatically Shabbat, without the need for any declaration on the part of the Jewish people. Rather, amend it and say as follows: Who sanctifies Shabbat, the Jewish people, and the seasons, as the Jewish people indeed sanctify the New Moon and the Festival days. Rav Yosef said: The halakha with regard to the conclusion of the blessing is in accordance with the opinion of Rabbi Yehuda HaNasi and as the difficulty was resolved by Ravina. (Beitza 17a - hattip: @DonielF)

Regardless, there is no reason to connect Sabbath to Saturday specifically, and, indeed, it is generally assumed that in regions over the secular date line, Sabbath may fall out instead on Friday/Sunday.

  • 1
    Indeed, in New Zealand, because of the question/disagreement regarding the location of the halachic Date Line, they observe a "shabbos lite" on Sunday, when they don't violate any d'oraisa prohibitions (as I understand it).
    – Jeffiekins
    Commented Jul 31, 2018 at 22:13
  • I think you might be suprised that some Poskim do consider the international date line (Saurday) to be relevent to determining when Shabbos comes, [either "miikar hadin (primary halacha) or as a way to chose between conflicting opinions] Commented Oct 12, 2023 at 1:55

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .