If form classes are defined in terms of the frames in which they occur and the frames themselves consist of form classes, wouldn’t that be defining in a circle, since one wouldn’t know when and where to begin with the first form classes and first frames? To answer this, we have to resort to what Bloomfield (Lg, 164 - 165) calls “selection”. There are many complicated phases of the grammatical concept selection, but the essential idea is the fact that certain forms arbitrarily behave alike in one way and certain others behave alike in another. To make selection applicable in grammar, however, it would be necessary to have a complete lexicon of the language with the form classes all marked. In fact, most grammarians grant the necessity of including the whole lexicon in order to have a complete grammar of a language. Otherwise, there is no way to set up grammatical rules in order to know, to use Bloomfield’s examples, that ‘prince’, ‘author’, ‘sculptor’ take the suffix -ess, while ‘king’, ‘singer’, ‘painter’ do not. A lexicon of the language, with all form classes of the entries properly indicated, is the ultimate answer to the question of selection.
 Chao Y R. A grammar of spoken Chinese[M]. Univ of California Press, 1965.