Concept structures form a continuum defined by how far substitutes are permitted.

Evidence

Chapter 5 shows that one can think of different concept structures in terms of substitutability (Most and Starr 1989). Necessary conditions can be defined as those that do not permit substitutes. In contrast, the family resemblance approach is characterized by the fact that the absence of one characteristic can be substituted for by the presence of others. The continuum that connects the necessary and sufficient condition and family resemblance poles is thus the degree to which substitutability is possible. — Gary Goertz, Social Science Concepts, 58

Categorization

• DEFINE: Gives a crisp operational definition of “substitutability” that converts vague typologies into a measurable dimension.
• XREF: Connects to any knowledge-base material on necessary/sufficient conditions, family resemblance (Wittgenstein), and measurement validity in social science.