Most form classes, even not counting phrases, are of unlimited membership, short of complete enumeration through the whole lexicon of the language. At the other extreme, a form class may have only one member, such as the subordinative particle de. Between the two extremes there are the relatively short lists such as the class of simple numerals, personal pronouns, auxiliary verbs, and aspect suffixes, which can be exhaustively enumerated or even memorized. In the preceding example of a noun being defined as that which can be modified by a D-M compound, we were defining an open class in terms of (closed) lists, namely, determinatives (D) and measures (M). Proceeding thus from the listables to the unlistables, we can define the unknown by the known and thus break the circularity we were concerned about above. This does not eliminate the usefulness of going to meaning, but will free the study of form from dependence on the study of meaning. But grammatical meaning does have a positive correlation with real meaning, since linguistic forms, after all, have evolved out of their use in life.
[1] Chao Y R. A grammar of spoken Chinese[M]. Univ of California Press, 1965.
