Must a Definition Find One Essence Shared by Every Case?

We often assume that a concept has not been properly defined unless we can list necessary conditions shared by every instance. If chess, football, card play and children's chasing activities are all called games, it seems that one common essence must lie behind them.

The later Wittgenstein challenged that demand. When we actually compare games, competition, amusement, rules, winning and skill each cover only some cases. No single feature runs through them all. Their relationship is more like resemblance within a family: eyes, gait and facial shape overlap across different members without one feature being shared by everyone. Wittgenstein called this “family resemblance”.

This does not make definitions arbitrary. Concepts still need boundaries, but those boundaries may be sustained by a stable network of similarities and uses rather than one inner core. My view is that a definition first has to make distinction and communication work reliably. Some scientific concepts require strict necessary and sufficient conditions; some everyday concepts remain stable only within a network of use. Imposing one model of definition on every concept creates false precision.

https://plato.stanford.edu/entries/wittgenstein/
https://plato.stanford.edu/entries/concepts/