Negative-case universes remain undefined even when core concepts are clearly specified.

Evidence

Much trickier are the issues surrounding how concepts are used to select the negative cases. Skocpol (1979) is quite clear about what social revolution is, but it is not at all clear what the universe of non– social revolutions consists of. Here we see a very significant problem linking concepts to research design, the nature of “non” concepts, which typically define the negative cases needed to test hypotheses and theories. — Gary Goertz, Social Science Concepts, 105

Categorization

• DEFINE: Introduces the concept of ‘non’ concepts — the implicit definitional category that supplies negative cases.
• QUESTION: How would one actually enumerate the universe of non-social-revolutions? Worth chasing for any comparative design.