Concept structures differ by how far their attributes can substitute for each other.

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, 119

Categorization

• DEFINE: Substitutability gives a single scalar that unifies the necessary-and-sufficient and family-resemblance poles instead of treating them as rival typologies.
• XREF: Connects to the reader’s institutional-design reading (Milgrom on reputation bonds, diamond-bourse extralegal regimes) where substitutable safeguards trade off against necessary ones.