A good social-science definition states exactly which attributes are necessary and sufficient.

Evidence

In classic fashion, Skocpol defines social revolution using a necessary and sufficient condition structure: “Social revolutions are rapid, basic transformations of a society’s state and class structures; and they are accompanied and in part carried through by class-based revolts from below” (1979, 4–5). This definition holds that social revolutions are the combination of three components: (1) class-based revolts from below, (2) rapid and basic transformation of state structures, and (3) rapid and basic transformation of class structures. Skocpol is explicit that if any one of these three attributes is missing, the case in question cannot be considered a social revolution. In this sense, each of the three attributes is necessary for social revolution. Skocpol also strongly implies that the simultaneous presence of the three components is sufficient for an event to be classified as a social revolution: any case that contains her three components is definitely a social revolution. — Gary Goertz, Social Science Concepts and Measurement, 1561

Categorization

• DEFINE: Shows what a necessary-and-sufficient condition structure looks like concretely, using Skocpol’s three-component definition as the model case.
• XREF: Connects to the reader’s existing interest in institutional and concept-formation theory — necessary/sufficient conditions recur across causal-inference and measurement work.