If the position of the trace in (99c) were only relatively inaccessible to movement, the appearance of parasitic gaps in domains relatively inaccessible to ordinary extraction is, apparently, determined by irrelevant intervening contexts in selectional rules. We will bring evidence in favor of the following thesis: a subset of English sentences interesting on quite independent grounds does not readily tolerate the strong generative capacity of the theory. Notice, incidentally, that the notion of level of grammaticalness is not to be considered in determining the requirement that branching is not tolerated within the dominance scope of a complex symbol. Clearly, any associated supporting element suffices to account for an important distinction in language use. With this clarification, the earlier discussion of deviance can be defined in such a way as to impose a general convention regarding the forms of the grammar.
see also: WikiPedia -- Chomskybot