5.4.6 Subcategorization of the lexicon

　 In 5.4.1 it is mentioned that phrase structure rules and lexicon together generate the deep structure of the sentence. The lexicon is the total vocabulary stored in the mind. Speakers of any language know tens of thousands of words. They know how to pronounce them, what they mean and what lexical categories they belong to. Phrase structure rules specify what lexical categories are the constituents of what phrasal categories. But the words of a lexical category must be further classified before they are put into a phrase or sentence. Can the verb put be inserted in the following tree diagrams?

　　
　　The answer is No, because we know that the verb put requires an NP followed by a PP or Adv (Represented formally as: Put, V---NP PP/Adv). The process of putting words of the same lexical category into smaller classes according to their syntactic characteristics is called subcategorization (Traditional grammar has done a better job in this respect).