Full Idea
The definition theory says that concepts are complex structures which entail their constituents. By saying this, it guarantees both the connection between content and necessity, and the connection between concept individuation and concept possession.
Gist of Idea
Definable concepts have constituents, which are necessary, individuate them, and demonstrate possession
Source
Jerry A. Fodor (Concepts:where cogn.science went wrong [1998], Ch.5)
Book Reference
Fodor,Jerry A.: 'Concepts: where cognitive science went wrong' [OUP 1998], p.88
A Reaction
He cites Pinker as a spokesman for the definitional view. This is the view Fodor attacks, in favour of his atomistic account. He adds in a note that his view also offered to reduce conceptual truth to logical truth.