On our assumptions, a descriptively adequate grammar raises serious doubts about the system of base rules exclusive of the lexicon. For one thing, the speaker-hearer's linguistic intuition is not to be considered in determining an abstract underlying order. Analogously, an important property of these three types of EC delimits the requirement that branching is not tolerated within the dominance scope of a complex symbol. It may be, then, that the systematic use of complex symbols suffices to account for the strong generative capacity of the theory. Conversely, relational information does not readily tolerate a general convention regarding the forms of the grammar.
see also: WikiPedia -- Chomskybot