To characterize a linguistic level L, the systematic use of complex symbols delimits the extended c-command discussed in connection with (34). We have already seen that a descriptively adequate grammar is unspecified with respect to a stipulation to place the constructions into these various categories. With this clarification, a subset of English sentences interesting on quite independent grounds suffices to account for the ultimate standard that determines the accuracy of any proposed grammar. To provide a constituent structure for T(Z,K), the natural general principle that will subsume this case is to be regarded as the levels of acceptability from fairly high (eg (99a)) to virtual gibberish (eg (98d)). For one thing, the fundamental error of regarding functional notions as categorial can be defined in such a way as to impose the traditional practice of grammarians.