Middle-Sized Theories

This paper argues in defense of middle-sized (or ‘middle-level’) scientific theories and middle-sized principles. Our arguments derive from consideration of successful scientific practice. Focusing on middle-sized theories of change and the middle-sized principles they engage, we set out two case studies from differing areas of application: (1) the development of new technology – masers and lasers in particular; and (2) policy design in social domains, such as welfare, education and health, using a sugar sweetened beverage tax as illustration. We show the central use of middle-sized theories of change and middle-sized principles in these two areas and contend that this illustrates their vital role more generally.