Chomsky has claimed that «the language each person acquires is a rich and complex
construction hopelessly underdetermined by the fragmentary evidence available», that
is, the grammar acquired by children is much more complex than one should expect
on the basis of the language data the children is exposed to from people around them.
Geoffrey Sampson points out that «Chomsky originally made statement about
the child’s data being quantatively poor years before anyone had done serious
research on the nature of the speech addressed to children», and that later research has
not supported Chomsky’s statement.