Semichah: the ordination that was broken off סמיכה

Where it comes from. "And he laid his hands upon him and charged him"—so Moses appointed Joshua (Numbers 27:23). From that laying on of hands comes the word: semichah.

How it was done. Not by literally laying on hands but by naming: "They ordain him by name by announcing it publicly; he is called Rabbi, and they give him permission to adjudicate cases involving laws of fines" (Sanhedrin 13b). Three perform it, of whom at least one is himself ordained.

What it gave. The right to judge what only an ordained court may judge: the monetary fines of the Torah, corporal punishment, capital cases. An ordinary court without semichah judges only what the sages established.

How it broke. Semichah was given only in the Land of Israel. Roman persecution after the Bar Kokhba revolt made it punishable by death: Rabbi Yehuda ben Bava ordained five students in the hills and was killed for it. It held on two centuries more and broke off about 4120.

Can it be restored. The Rambam says: "If all the wise men in the Land of Israel agree to appoint judges and convey semichah upon them, the semichah is binding, and these judges may adjudicate cases involving fines" (Sanhedrin 4:11). On this stood the attempt of 5298 in Safed: Rabbi Yaakov Berab gathered the sages and gave semichah to four. Rabbi Levi ibn Habib of Jerusalem objected that "all the wise men" means all, not those assembled; the dispute is unresolved to this day, and in that sense there is still no semichah.

Why this matters for the reckoning of time. While semichah existed, the court of the Land of Israel could declare the new month on the evidence of witnesses and insert a thirteenth month. When it broke off, the calendar had to be put on calculation—and calculated it has been ever since.