Nominal typologies often conceal a two-poled continuum with a gray zone.

Evidence

For example, sticking with democracy, a standard typology is (1) parliamentary, (2) presidential, and (3) mixed or semipresidential. Should one think of that as a three-part nominal typology, or as a concept pair with parliamentary and presidential at the ends and mixed in the middle? I argue below that instead of it being a nominal typology, it is better thought of as a presidential–parliamentary concept pair with a gray zone in the middle for “mixed” or “semi.” — Gary Goertz, Social Science Concepts and Measurement, 1201

Categorization

• DEFINE: Distinguishes nominal typologies from concept pairs with an underlying dimension — the chapter’s key conceptual move.