A subordinate clause, dependent clause, subclause, or embedded clause is a clause that is embedded within a complex sentence. For instance, in the English sentence "I know that Bette is a dolphin", the clause "that Bette is a dolphin" occurs as the complement of the verb "know" rather than as a freestanding sentence. Subtypes of dependent clauses include content clauses, relative clauses, and adverbial clauses. Content clause A content clause, also known as a "noun clause", provides content implied or commented upon by its main clause. It can be a subject, predicate nominative, direct object, appositive, indirect object, or object of the preposition. Some of the English words that introduce content clauses are that, who (and formal whom), whoever (and formal whomever), whether, why, what, how, when, and where. Notice that some of these words also introduce relative and adverbial clauses. A clause is a content clause if a pronoun (he, she, it, or they) could be substituted for it. Examples: I know who said that. (I know them. The dependent clause serves as the object of the main-clause verb "know".) Whoever made that assertion is wrong. (They are wrong. The dependent clause serves as the subject of the main clause.) In English, in some instances the subordinator that can be omitted. Example 1: I know that he is here. I know he is here. Example 2: I think that it is pretty. (less common) I think it is pretty. (more common) Relative (adjectival) clause In Indo-European languages, a relative clause, also called an adjectival clause or an adjective clause, meets three requirements: Like all dependent clauses, it contains a verb (and also a subject unless it is a non-finite dependent clause). However, in a pro-drop language the subject may be a zero pronoun: the pronoun may not be explicitly included because its identity is conveyed by a verbal inflection. It begins with a relative adverb [when, where, how, or why in English] or a relative pronoun [who, whom, whose, that, what or which in English]. However, the English relative pronoun (other than what) may be omitted and only implied if it plays the role of the object of the verb or object of a preposition in a restrictive clause; for example, He is the boy I saw is equivalent to He is the boy whom I saw, and I saw the boy you are talking about is equivalent to