Using that as a complementizer is helpful when certain verbs (e.g., shows, says, indicates, proves) are used to introduce a clause instead of a direct or indirect object: He said [that] "The Thin Red Line" is his favorite movie.

What is a complementizer in a sentence?

In linguistics (especially generative grammar), complementizer or complementiser (glossing abbreviation: comp) is a functional category (part of speech) that includes those words that can be used to turn a clause into the subject or object of a sentence. ... The standard abbreviation for complementizer is C.

How do you identify a complementizer in a sentence?

In English grammar, a complementizer is a word used to introduce a complement clause, including subordinate conjunctions, relative pronouns, and relative adverbs. For example, it functions as a complementizer in the sentence, "I wonder if she will come."