In grammar, a clause is a pair or group of words that consist of a subject and a predicate, although in some languages and some types of clauses, the subject may not appear explicitly as a noun phrase. It may instead be marked on the verb (this is especially common in null subject languages.) The most basic kind of sentence consists of a single clause; more complicated sentences may contain multiple clauses, including clauses contained within clauses.

Clauses are often contrasted with phrases. Traditionally, a clause was said to have both a finite verb and its subject, whereas a phrase either contained a finite verb but not its subject (in which case it is a verb phrase) or did not contain a finite verb. Hence, in the sentence "I didn't know that the dog ran through the yard," "that the dog ran through the yard" is a clause, as is the sentence as a whole, while "the yard," "through the yard," "ran through the yard," and "the dog" are all phrases. However, modern linguists do not draw the same distinction, as they accept the idea of a non-finite clause, a clause that is organized around a non-finite verb.

Functions of dependent clauses

One way to classify dependent clauses is by function; that is, by the roles they play in the clauses they are subordinate to. Since the same dependent clause might have different roles in different sentences, this classification must be applied on a per-sentence basis.

Under this classification scheme, there are three main types of dependent clauses: noun clauses, adjective clauses, and adverb clauses, so called for their syntactic and semantic resemblance to noun phrasea verb or preposition, as in these English examples:

• "What you say is not as important as how you say it."
• "I imagine that they're having a good time."
• "I keep thinking about what happened yesterday."

(Note that the word that is optional in the second sentence, highlighting a complication in the entire dependent/independent contrast: "They're having a good time" is a complete sentence, and therefore an independent clause, but in "I imagine they're having a good time," it acts as a dependent clause.)

An adjective clause modifies a noun phrase. In English, adjective clauses typically come at the end of their noun phrases:

• "The woman I spoke to said otherwise."
• "We have to consider the possibility that he's lying to us."

An adverb clause typically modifies its entire main clause. In English, it usually precedes or follows its main clause:

• "When she gets here, all will be explained."
• "He was annoyed by the whole thing, which was unfortunate, but unavoidable (vague)."