On our assumptions, the speaker-hearer's linguistic intuition is not quite equivalent to an important distinction in language use. Analogously, a descriptively adequate grammar may remedy and, at the same time, eliminate a parasitic gap construction. Thus the appearance of parasitic gaps in domains relatively inaccessible to ordinary extraction is to be regarded as an abstract underlying order. Nevertheless, a case of semigrammaticalness of a different sort is necessary to impose an interpretation on the requirement that branching is not tolerated within the dominance scope of a complex symbol. However, this assumption is not correct, since relational information does not readily tolerate a stipulation to place the constructions into these various categories.
see also: WikiPedia -- Chomskybot