What is "complementizer"

alt. (context linguistics English) a form of subordinate conjunction n. (context linguistics English) a form of subordinate conjunction

In linguistics (especially generative grammar), complementizer or complementiser ( glossing abbreviattion: ) is a lexical category (part of speech) that includes those words that can be used to turn a clause into the subject or object of a sentence. For example, the word that may be called a complementizer in English sentences like Mary believes that it is raining. The concept of complementizers is specific to certain modern grammatical theories; in traditional grammar, such words are normally considered either conjunctions or relative pronouns.

The standard abbreviation for complementizer is C. The complementizer is often held to be the syntactic head of a full clause, which is therefore often represented by the abbreviation CP (for complementizer phrase). Evidence that the complementizer functions as the head of its clause includes the fact that it is commonly the last element in a clause in head-final languages like Korean or Japanese, in which other heads follow their complements, whereas it appears at the start of a clause in head-initial languages such as English, where heads normally precede their complements.