Any organised society needs some method for determining common policy: public decisions must be forged from private preferences, and particular interests must find a reconciliation in the general good. A society is tolerable only if its decisions are reached by a rational path; for, just as a reasonable man decides his private life on the basis of reasonable procedures, so a reasonable society must formulate its communal behaviour on the basis of reasonable principles. If the Principle of Rationality is violated, society collapses into an anarchic tohubohu, governed by naked power or arbitrary caprice.