A syntactic category is a type of syntactic unit that theories of syntax assume. The traditional parts of speech (e.g. noun, verb, preposition, etc.) are syntactic categories, and in phrase structure grammars, the phrasal categories (e.g. noun phrase, verb phrase, preposition phrase, etc.) are also syntactic categories. Phrase structure grammars draw an important distinction between lexical and phrasal categories. Dependency grammars, in contrast, do not acknowledge phrasal categories (at least not in the traditional sense), which means they work with lexical categories alone.
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The three criteria used in defining syntactic categories are:
For instance, many nouns in English denote concrete entities, they are pluralized with the suffix -s, and they occur as subjects and objects in clauses. Many verbs denote actions or states, they are conjugated with agreement suffixes (e.g. -s of the third person singular in English), and in English they tend to show up in medial positions of the clauses in which they appear.
The traditional parts of speech are known as lexical categories. Traditional grammars tend to acknowledge approximately eight to twelve lexical categories, e.g.
The lexical categories that a given grammar assumes will likely vary from this list. Certainly numerous subcategories can be acknowledged. For instance, one can view pronouns as a subtype of noun, and verbs can be divided into finite verbs and non-finite verbs (e.g. gerund, infinitive, participle, etc.).
The central lexical categories give rise to corresponding phrasal categories:
In terms of phrase structure rules, phrasal categories can occur to the left of the arrow while lexical categories cannot. Traditionally, a phrasal category should consist of two or more words, although conventions vary in this area. X-bar theory, for instance, often sees individual words as corresponding to phrasal categories. Phrasal categories are illustrated with the following trees:
The lexical and phrasal categories are identified according to the node labels, phrasal categories receiving the "P" designation.
Dependency grammars do not acknowledge phrasal categories in the way that phrase structure grammars do. What this means is that the distinction between lexical and phrasal categories disappears, the result being that only lexical categories are acknowledged. The tree representations are simpler because the number of nodes and categories is reduced, e.g.
The distinction between lexical and phrasal categories is absent here. The number of nodes is reduced buy removing all nodes marked with "P". Note, however, that phrases can still be acknowledged insofar as any complete subtree that contains two or more words will qualify as a phrase.