Noun clauses are subordinate clauses that function as nouns and usually begin with introductory words like that, which, who, when, where, what, how, why, whether. Noun clauses can serve as subjects, objects, or objects of prepositions. They contain both a subject and a verb. Common introductory words that start noun clauses are that, which, who, whom, whose, when, where, whenever, what, how, why, whether, whoever, whomever, whichever, wherever.