Rabbi Dr. Jonathan Romain responds to the question: What is the origin of a minyan being ten men?
There is a strong tradition within Judaism of communal prayer for the regular daily or Sabbath services. One can always say one’s own prayers by oneself, and any time and in any place, but having others around you brings a sense of camaraderie, can help you pray when you are not in the mood, and be a source of comfort when you are facing problems; equally, your presence can help others when they are in any of those same situations. If you look at any service, you will notice that virtually all of the prayers are in the plural and refer to ‘we’ or ‘our’ or ‘us’. The one exception is the beginning of the Amidah (‘My God, open my mouth and let my lips declare Your praise’), and traditionally that line is said to oneself.
In order to encourage people to come together, it was established that without a quorum/minyan, one could not say key parts of the service eg reciting Kaddish or reading from the Torah. There are many explanations as to why ten was chosen: one is that on Noah’s Ark, there were eight people (Noah, his three sons and their wives) plus the divine spirit, and that was not enough to save the world from destruction (whereas ten might have done so !). Similarly, God agreed to spare the cities of Sodom and Gomorrah if there were ten righteous people there. Another is that Psalm 82.1 says that ‘God stands in the congregation’ and elsewhere that same Hebrew word (eidah) is used of the ten spies who brought back a negative report on the Land of Israel.
Orthodox synagogues insist this quorum be made up of be ten adult males (ie over the age of 13), whereas Reform will count ten individuals, recognising women as fully equal. Many Reform rabbis will allow Kaddish to be said even if a minyan is absent so as not to penalise mourners because of those who did not attend.