Full Idea
Nothing in any mental life could be the concept CAT unless it is satisfied by cats. If you haven't got a concept that applies to cats, that entails that you haven't got the CAT concept.
Gist of Idea
It is essential to the concept CAT that it be satisfied by cats
Source
Jerry A. Fodor (Concepts:where cogn.science went wrong [1998], Ch.2)
Book Reference
Fodor,Jerry A.: 'Concepts: where cognitive science went wrong' [OUP 1998], p.25
A Reaction
Of course, having a concept that applies to cats doesn't entail that you have the CAT concept. Quine's 'gavagai', for example. I think Fodor is right in this idea.