In linguistics, complementizer or complementiser is a lexical category that includes those words that can be used to turn a clause into the subject or object of a sentence. For example, the wordthat 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 conjunctions. 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. Evidence that the complementizer functions as the head of its clause includes 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.
Types and development
It is common for the complementizers of a language to develop historically from other syntactic categories. Across the languages of the world, it is especially common for pronouns or determiners to be used as complementizers. Another frequent source of complementizers is the class of interrogative words. It is especially common for a form that otherwise means what to be borrowed as a complementizer, but other interrogative words are often used as well; e.g., colloquial English I read in the paper how it's going to be cold today, with unstressed how roughly equivalent to that. English for in sentences like I would prefer for there to be a table in the corner shows a preposition that has arguably developed into a complementizer. In many languages of West Africa and South Asia, the form of the complementizer can be related to the verb say. In these languages, the complementizer is also called the quotative. The quotative performs many extended functions in these languages.
Empty complementizers
Some analyses allow for the possibility of invisible or "empty" complementizers. An empty complementizer is considered to be present when there is not a word, even though the rules of grammar expect one. The complementizer is usually said to be understood – i.e., an English speaker knows it is there, and so it does not need to be said. Its existence in English has been proposed based on the following type of alternation: Because that can be inserted between the verb and the embedded clause without changing the meaning, the original sentence without a visible complementizer would be reanalyzed as Where the symbol øC represents the empty complementizer. This suggests another interpretation of the earlier "how" sentence: where "how" serves as a specifier to the empty complementizer. This allows for a consistent analysis of another troublesome alternation: where "OP" represents an invisible interrogative known as an operator. In a more general sense, the proposed empty complementizer parallels the suggestion of near-universal empty determiners.
In Assyrian Neo-Aramaic, a modern Aramaic language, kat is used as a complementizer and is related to the relativizer. Though it is less common in casual speech, and more so in formal conversation.
In Hebrew two complementizers coexist: שֶ, which is either related to the relativizer ‘asher and/or to the pronominal Proto-Semitic dhu ; and כִּי , which is also used as a conjunction meaning 'because, when'. In modern usage, the latter is reserved for more formal writing.
