Ten, Derived from a Complaint in the Wilderness

The requirement of ten adult participants for certain prayers is not a round convenience but a specific rabbinic derivation from scripture. The Talmud traces the number to the account in the book of Numbers of the twelve spies sent to scout Canaan, ten of whom returned with a discouraging report; that group of ten is called an evil congregation, and the rabbis reasoned from the word used there that a congregation, in the sense the law cares about, numbers at least ten.

From that reading followed a fixed list of acts that require the quorum to be present at all: the public reading of the Torah, the repetition of the standing prayer known as the Amidah, the recitation of the mourner's Kaddish, and the seven blessings recited at a wedding, among others, all of which a person praying alone may not perform in their full communal form. The requirement shaped synagogue life practically, since a small or declining community's ability to hold a full service depends on reliably finding ten. Reform Judaism, from the twentieth century, extended the count to women alongside men, while Orthodox practice has generally continued to count only men, so that the same historical derivation from a single verse now produces two different quorums in different parts of the same tradition.