In linguistics, subcategorization denotes the ability/necessity for lexical items (usually verbs) to require/allow the presence and types of the syntactic arguments with which they co-occur. The notion of subcategorization is similar to the notion of valency, although the two concepts (subcategorization and valency) stem from different traditions in the study of syntax and grammar.
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Examples
While subcategorization is a concept that can apply to almost any type of lexical item, it is usually discussed with respect to verbs. Verbs that take just one argument are classified as intransitive, while verbs with two and three arguments are classified as transitive and ditransitive, respectively. The following sentences are employed to illustrate the concept of subcategorization:
The verb worked/work is intransitive and thus subcategorizes for a single argument (here Luke), which is the subject; therefore its subcategorization frame contains just a subject argument. The verb ate/eat is transitive, so it subcategorizes for two arguments (here Indiana Jones and chilled monkey brain), a subject and an optional object, which means that its subcategorization frame contains two arguments. And the verb waited/wait subcategorizes for two arguments as well, although the second of these is an optional prepositional argument associated with the preposition for. In this regard, we see that the subcategorization frame of verbs can contain specific words. Subcategorization frames are sometimes schematized in the following manner:
These examples demonstrate that subcategorization frames are specifications of the number and types of arguments of a word (usually a verb), and they are believed to be listed as lexical information (that is, they are thought of as part of a speaker's knowledge of the word in the vocabulary of the language). Dozens of distinct subcategorization frames are needed to accommodate the full combinatory potential of the verbs of any given language. Finally, subcategorization frames are associated most closely with verbs, although the concept can also be applied to other word categories.
Subcategorization frames are essential parts of a number of phrase structure grammars, e.g. Head-Driven Phrase Structure Grammar, Lexical Functional Grammar, and Minimalism.
The status of subjects
The subcategorization notion is similar to the notion of valency, although subcategorization originates with phrase structure grammars in the Chomskyan tradition, whereas valency originates with Lucien Tesnière of the dependency grammar tradition. The primary difference between the two concepts concerns the status of the subject. As it was originally conceived of, subcategorization did not include the subject, that is, a verb subcategorized for its complement(s) (=object and oblique arguments) but not for its subject. Many modern theories now include the subject in the subcategorization frame, however. Valency, in contrast, included the subject from the start. In this regard, subcategorization is moving in the direction of valency, since many phrase structure grammars now see verbs subcategorizing for their subject as well as for their object(s).