Family resemblance concepts operate on sufficiency alone, letting one feature substitute for another.

Evidence

In the history of philosophy it was Wittgenstein who introduced the notion of family resemblance, exactly as a contrast with the Aristotelian, necessary and sufficient condition approach to conceptualization. In contrast to the classic Aristotelian approach, family resemblance specifically denies that any feature is necessary. One only has sufficiency requirements. In terms of substitutability, the absence of one feature can be compensated for by the presence of another. — Gary Goertz, Social Science Concepts and Measurement, 1367

Categorization

• DEFINE: Defines family resemblance by contrast with necessary-and-sufficient definitions: no feature is necessary, only jointly sufficient.
• XREF: Standard philosophical anchor for prototype and cluster concepts in cognitive psychology (Rosch).