why are the [theory] propositions as specified … Why do the relationships hold? Answers to this question are what give the theory explanatory power (Type II and Type IV theories). Parts of this may already be provided in the propositions established above. Explanatory power may also arise from a theory’s interaction in a research context.

D. I. K. Sjøberg, T. Dybå, B. C. D. Anda, and J. E. Hannay, “Building Theories in Software Engineering,” in Guide to Advanced Empirical Software Engineering SE - 12, F. Shull, J. Singer, and D. K. Sjøberg, Eds. Springer London, 2008, pp. 312–336. [Springerlink]