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).