We will bring evidence in favor of the following thesis: relational information appears to correlate rather closely with the traditional practice of grammarians. A consequence of the approach just outlined is that the theory of syntactic features developed earlier is necessary to impose an interpretation on a descriptive fact. Suppose, for instance, that the natural general principle that will subsume this case does not readily tolerate an abstract underlying order. Let us continue to suppose that an important property of these three types of EC is, apparently, determined by a parasitic gap construction. Nevertheless, the notion of level of grammaticalness can be defined in such a way as to impose a general convention regarding the forms of the grammar.
see also: WikiPedia -- Chomskybot