Relative clause

A relative clause is a clause that modifies a noun or noun phrase and uses some grammatical device to indicate that one of the arguments in the relative clause refers to the noun or noun phrase. For example, in the sentence I met a man who wasn't too sure of himself, the subordinate clause who wasn't too sure of himself is a relative clause since it modifies the noun man and uses the pronoun who to indicate that the same "MAN" is referred to in the subordinate clause (in this case as its subject).

In many languages, relative clauses are introduced by a special class of pronouns called relative pronouns, such as who in the example just given. In other languages, relative clauses may be marked in different ways: they may be introduced by a special class of conjunctions called relativizers, the main verb of the relative clause may appear in a special morphological variant, or a relative clause may be indicated by word order alone. In some languages, more than one of these mechanisms may be possible.

A bound relative clause, the type most often considered, qualifies an explicit element (usually a noun or noun phrase) appearing in the main clause, and refers back to that element by means of some explicit or implicit device within the relative clause.

The relative clause may also function as an embedded clause within a main (or higher-level) clause, thereby forming a matrix sentence. The noun in the main clause that the relative clause modifies is called the head noun, or (particularly when referred back to by a relative pronoun) the antecedent.

For example, in the English sentence "The person whom I saw yesterday went home", the relative clause "whom I saw yesterday" modifies the head noun person, and the relative pronoun whom refers back to the referent of that noun. The sentence is equivalent to the following two sentences: "I saw a person yesterday. That person went home". The shared argument need not fulfill the same role in both clauses; in this example the same person is referred to by the subject of the matrix clause, but the direct object of the relative clause.

A free relative clause (or fused relative), on the other hand, does not have an explicit antecedent external to itself. Instead, the relative clause itself takes the place of an argument in the matrix clause. For example, in the English sentence "I like what I see", the clause what I see is a free relative clause, because it has no antecedent, but itself serves as the object of the verb like in the main clause. Alternatively, one could argue that the free relative clause has a zero as its antecedent.

Bound relative clauses may or may not be restrictive. A restrictive relative clause is a relative clause that functions as a restrictive modifier. A non-restrictive relative clause is a relative clause that is not a restrictive relative clause. Whereas a non-restrictive or non-defining relative clause merely provides supplementary information, a restrictive or defining relative clause modifies the meaning of its head word (restricts its possible referent). For example:

In speaking, it is natural to make slight pauses around non-restrictive clauses, and in English this is shown in writing by commas (as in the examples). However, many languages distinguish the two types of relative clauses in this way only in speaking, not in writing. Another difference in English is that only restrictive relative clauses may be introduced with that or use the "zero" relative pronoun (see English relative clauses for details).