In grammar, a clause is the smallest grammatical unit that can express a complete proposition. In some languages it may be a pair or group of words that consists of a subject and a predicate, although in other languages in certain clauses the subject may not appear explicitly as a noun phrase, being instead marked on the verb (this is especially common in null subject languages). The most basic kind of sentence consists of a single (independent) clause. More complex sentences may contain multiple clauses. Clauses may be independent or dependent. Independent clauses are those that could stand as a sentence by themselves, although they may be used connected with other clauses in a longer sentence. Dependent clauses are those that would be awkward or nonsensical if used alone, and must be used in a sentence also containing an independent clause.
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. Technically, a phrase is any group of words that function together as a single part of speech. 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.
Structures of dependent clauses
Dependent clauses may be classified by their structure, although this classification does make some reference to the clause's function in a sentence. This scheme is more complex than analysis by function, as there are many different ways that a dependent clause can be structured. In English. Common structures include the following:
- Many dependent clauses, such as "before he comes" or "because they agreed," consist of a preposition-like subordinating conjunction, plus what would otherwise be an independent clause. These clauses act much like prepositional phrases, and are either adjective clauses or adverb clauses, with many being able to function in either capacity.
- Relative clauses, such as "which I couldn't see," generally consist of a relative pronoun, plus a clause in which the relative pronoun plays a part. Relative clauses usually function as adjective clauses, but occasionally they function as adverb clauses; in either case, they modify their relative pronoun's antecedent and follow the phrase or clause that they modify.
- Fused relative clauses, such as "what she did" (in the sense of "the thing she did"), are like ordinary relative clauses except that they act as noun clauses; they incorporate their subjects into their relative pronouns.
- Declarative content clauses, such as "that they came," usually consist of the conjunction that plus what would otherwise be an independent clause, or of an independent clause alone (with an implicit preceding that). For this reason, they are often called that-clauses. Declarative content clauses refer to states of affairs; it is often implied that the state of affairs is the case, as in "It is fortunate that they came," but this implication is easily removed by the context, as in "It is doubtful that they came."
- Interrogative content clauses, such as "whether they came" and "where he went" (as in "I don't know where he went"), are much like declarative ones, except that they are introduced by interrogative words. Rather than referring to a state of affairs, they refer to an unknown element of a state of affairs, such as one of the participants (as in "I wonder who came") or even the truth of the state (as in "I wonder whether he came").
- Small clauses, such as "him leave" (as in "I saw him leave") and "him to leave" (as in "I wanted him to leave"), are minimal predicate structures, consisting only of an object and an additional structure (usually an infinitive), with the latter being predicated to the former by a controlling verb or a preposition.
- Kroeger, Paul (2005). Analysing Grammar: An Introduction. Cambridge: Cambridge University Press. pp. 32. ISBN 978-0-521-01653-7.