Throughout this book, the term sociological theory refers to logically interconnected sets of propositions from which empirical uniformities can be derived.  Throughout we focus on what I have called theories of the middle range: theories that lie between the minor but necessary working hypotheses that evolve in abundance during day-to-day research and the all-inclusive systematic efforts to develop a unified theory that will explain all the observed uniformities of social behavior, social organization, and social change (1968, p. 39).