Full Idea
Fodor argues that virtually all lexical concepts are innate, because most models of learning treat concept-learning as hypothesis testing, but that invariably employs the very concept to be learned.
Gist of Idea
If concept-learning is hypothesis-testing, that needs innate concepts to get started
Source
report of Jerry A. Fodor (The Language of Thought [1975]) by E Margolis/S Laurence - Concepts 3.3
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.13
A Reaction
The obvious response is to reject the theory which gave rise to this difficulty. I take concept formation to be a fairly mechanical and barely conscious response to environment, not a process of fully rational and conscious hypothesising.