So far, isolation as a tool of social analysis has been treated as an effect of geographical separation or of structural differentiation resulting in limitation of communication. Social distances are frequently based on other subtler forms of isolation.
The study of cultural differences between groups has revealed barriers quite as real and as effective as those of physical space and structure. Variations in language, folkways, mores, conventions, and ideals separate individuals and peoples from each other as widely as oceans and deserts. Communication between England and Australia is far closer and freer than between Germany and France.
Conflict groups, like sects and parties, and accommodation groups like castes and classes depend for survival upon isolation. Free intercourse of opposing parties is always a menace to their morale. Fraternization between soldiers of contending armies, or between ministers of rival denominations is fraught with peril to the fighting efficiency of the organizations they represent. The solidarity of the group, like the integrity of the individual, implies a measure at least of isolation from other groups and persons as a necessary condition of its existence.
The life-history of any group when analyzed is found to incorporate within it elements of isolation as well as of social contact. Membership in a group makes for increasing contacts within the circle of participants, but decreasing contacts with persons without. Isolation is for this reason a factor in the preservation of individuality and unity. The _esprit de corps_ and morale of the group is in large part maintained by the fixation of attention upon certain collective representations to the exclusion of others. The memories and sentiments of the members have their source in common experiences of the past from which non-members are isolated. This natural tendency toward exclusive experiences is often reinforced by conscious emphasis upon secrecy. Primitive and modern secret societies, sororities, and fraternities have been organized around the principle of isolation. Secrecy in a society, like reserve in an individual, protects it from a disintegrating publicity. The family has its "skeleton in the closet," social groups avoid the public "washing of dirty linen"; the community banishes from consciousness, if it can, its slums, and parades its parks and boulevards. Every individual who has any personality at all maintains some region of privacy.