'Imagine a person whose memory could not retain what the word 'pain' meant-so that he constantly called different things by that name-but nevertheless used the word in a way fitting in with the usual symptoms and presuppositions of pain'-in short he uses it as we all do. Here I should like to say: a wheel that can be turned though nothing else moves with it, is not part of the mechanism.

Philosophical investigations: (ed. 1958)