Glossary of Grammatical and Rhetorical Terms

In the title of this children's book by Dr. Seuss, the word that functions as a complementizer. (Random House, 1965)


In English grammar, a complementizer is a word used to introduce a complement clause (sometimes called a complement phrase).

Complementizers include subordinate conjunctions, relative pronouns, and relative adverbs. For example, if functions as a complementizer in the sentence "I wonder if she will come." 

In some contexts the complementizer that can be omitted—a process known as "that complementizer deletion." For example, "I wish that I had duck feet" can also be expressed as "I wish I had duck feet." The result is called a null complementizer.

In generative grammar, complementizer is sometimes abbreviated as Comp, COMP, or C.

See Examples and Observations below. Also see:


Examples and Observations

  • "The good news is that most older people are eligible for Medicare. The bad news is that Medicare does not pay for much long-term care."
    (Robert L. Kane, The Good Caregiver.  Avery, 2011)
  • "I think that people at the high end, people like myself, should be paying a lot more in taxes."
    (Warren Buffet, interview on This Week, November 21, 2010)

  • "I doubt if a single individual could be found from the whole of mankind free from some form of insanity."
    (Desiderius Erasmus)

  • That, If, and To as Complementizers
    "Complement types often have associated with them a word, particle, clitic, or affix whose function it is to identify the entity as a complement. Such forms are known as complementizers. . . . More than one complementizer may occur with a given complement type. Alternatively, some complement types may have no complementizer associated with them at all. In English, the particle that . . . is a complementizer associated with a complement type named after it, the that-clause. The particle if can also function as a complementizer with this same complement type, as in:
    (10) I don't know if Zeke knows Harry.
    Most infinitives have the complementizer to, but some have no complementizer. Neither the verbal noun nor participial complement types have complementizers in English."
    (Michael Noonan, "Complementation." Language Typology and Syntactic Description: Complex Constructions, ed. by Timothy Shopen. Cambridge University Press, 1985)

  • Complementizer That
    "In nominal clauses, that is called a complementizer: a word that creates a dependent clause that can substitute for a noun phrase sentence constituent. The resulting that-clause functions as a complement, a constituent that helps to complete the sentence. The complementizer that plays no role within its clause, nor does it contribute any information. Notice that if you remove the complementizer, what remains can stand alone as an independent clause:
    That the soccer game ended in a tie surprised no one
    The soccer game ended in a tie

    Our professor told us that there will be no exam next week.
    There will be no exam next week.
    All that does is connect two clauses, putting one inside the other at a position usually occupied by a noun or other nominal constituent."
    (Thomas P. Klammer, Muriel R. Schulz, and Angela Della Volpe, Analyzing English Grammar, 5th ed. Pearson, 2007)

  • Complementizers With Adverbial Clauses and Wh-Questions
    "Like the that-clause, the adverbial clause includes a fully formed S [sentence], with the similar restriction that it cannot be interrogative or imperative. Also like the that-clause, it begins with a complementizer, but in adverbial clauses, a much greater variety of lexical items serve as complementizers. We will need to revise our rule for Comp as follows:
    Comp- {while, since, because, although, if, when, so that, as, such, before, after, until, as long as, as soon as, by the time that, now that, once, inasmuch as . . .}
    Note that this is not an exhaustive listing of the complementizers. . . .

    "Like an adverbial clause, the wh-question always begins with a complementizer, in this case, who, whom, whose, what, which, why, when, where, and how. Note that with the exception of how, all of the complementizers begin with wh-, hence the name Wh- Words. However, an important difference between adverbial clauses and wh-questions is that the complementizer in the wh-clause, the wh-word, always has a function in its own clause. If the wh-word is removed, the clause usually becomes incomplete. Furthermore, the form of the wh-complementizer depends upon its function."
    (Laurel J. Brinton, The Structure of Modern English: A Linguistic Introduction. John Benjamins, 2000)

  • Recent Research on Complementizers
    "[A] close look at the properties and functions of complementizers has led to exciting developments in their study . . .. Hence, syntactic theory started out from conceiving Complementizer as the category responsible for introducing subordinate clauses and hosting moved wh-constituents; it has subsequently moved on to exploring the role of C in establishing the illocutionary force of sentences and to examining its central role in providing positions for constituents with a discourse-oriented role. Finally, syntactic theorizing took on the task of spelling out the Complementizer category's correlation with finiteness and, a fortiori, its close relation with category Tense . . .."
    (E. Phoevos Panagiotidis, "Introduction: Complementizers and Their Phase." The Complementiser Phase: Subjects and Operators. Oxford University Press, 2010)

    Alternate Spellings: complementiser