The individual character of one of these units seems to be largely a matter of convergent expectations—everyone's expectation of what everyone expects of everyone—with the new arrivals' expectations being molded in time to help mold the expectations of subsequent arrivals. There is a sense of "social contract," the particular terms of which are sensed and accepted by each incoming generation. I am told that this persistence of a tradition in a social entity is one of the reasons why the legal identity of an army division or regiment—its name and number and history—is often deliberately preserved when its strength has fallen to where abolition might seem indicated: the tradition that goes with the legal identity of the group is an asset worth preserving for a future buildup.

DEFINE: Defines the character of a social unit as a matter of convergent expectations forming a social contract.

Thomas C. Schelling, The Strategy of Conflict, loc. 223