Furthermore, the appearance of parasitic gaps in domains relatively inaccessible to ordinary extraction is not quite equivalent to the strong generative capacity of the theory. It may be, then, that the descriptive power of the base component cannot be arbitrary in the ultimate standard that determines the accuracy of any proposed grammar. In the discussion of resumptive pronouns following (81), a case of semigrammaticalness of a different sort delimits a parasitic gap construction. To characterize a linguistic level L, the natural general principle that will subsume this case is necessary to impose an interpretation on a stipulation to place the constructions into these various categories. Presumably, most of the methodological work in modern linguistics is to be regarded as a descriptive fact.
see also: WikiPedia -- Chomskybot