According to Boeke, it is not necessary that a society be dominated exclusively by one social system. If one social system does prevail, the society in question is a homogeneous society. When, on the contrary two (or more) social systems appear simultaneously, we have a dual society. Boeke qualifies the term dual society by using it only for societies "showing a distinct cleavage of two synchronic and full grown social styles which in the normal, historical evolution of homogeneous societies are separated from each other by transitional forms, as for instance, pre-capitalism and high capitalism by early capitalism."[1][2]
This qualification is necessary because every society going through the process of evolution or endogenic social progression shows besides the prevailing social systems, the remains of the preceding and the beginnings of its future social style. If, on the other hand, one social system is imported from abroad and this system fails to oust or assimilate the prevailing social system, a dual society obviously exists. On this account Boeke defines a dual society as a society where "one of the two prevailing social systems, as a matter of fact always the most advanced, will have been imported from abroad and have gained its existence in the new environment without being able to oust or assimilate the divergent social system that has grown up there, with the result that neither of them becomes general and characteristic for that society as a whole.