Robert Merton's middle range theory

The sociological conception of middle-range theory, proposed by Robert Merton (1957), comprises theory that is intermediate to daily practice and general theories. Middle range theory may appear similar to general theory in the sense that it involves abstractions but the abstractions in middle range theories can be supported by observed data. In development, when we are trying to bridge practice and theory, middle range theory is what we are looking at.
http://ssr1.uchicago.edu/PRELIMS/Theory/thmisc2.html