The Day the Diaspora Split From Shemini Atzeret and Israel Did Not

In much of the traditional Diaspora, Simchat Torah is kept as its own separate day, the twenty third of Tishrei, the date this rule records, a day after Shemini Atzeret rather than combined with it as Israeli practice keeps them. The split traces to the same historical mechanism that gives several other festivals an extra Diaspora day, the ancient uncertainty over confirmed new moon dates that led communities outside the Land of Israel to add a second day to festivals as a hedge, a custom that persisted as inherited practice even after the fixed calendar removed the practical need for it.

Because Shemini Atzeret itself is Diaspora observed across two days, and only the second of those two carries the Torah completion celebration in traditional practice, the Diaspora effectively gives the combined Sukkot conclusion three elements across two days where Israel compresses the same elements into one. The completion and restart of the Torah reading cycle, the practice both communities share regardless of which day carries it, remains the substance of the festival in either case, joyful processions with the scrolls, hakafot, marking Deuteronomy's end and Genesis's beginning read in the same service.