A poprelative pronoun is a pronoun that marks a relative clause within a larger sentence. In linguistics and grammar, a pronoun is a pro-form that substitutes for a noun or noun phrase with or without a determiner, such as you and they in English. ... A relative clause is a subordinate clause that modifies a noun. ... In linguistics, a sentence is a unit of language, characterized in most languages by the presence of a finite verb. ...

A relative pronoun links two clauses into a single complex clause. To this extent, it is similar in function to a subordinating conjunction. Unlike a conjunction, however, a relative pronoun stands in place of a noun. Compare:

(1) This is a house. Jack built this house.

(2) This is the house that Jack built.

Sentence (2) consists of two clauses, a main clause (This is the house) and a relative clause (that Jack built). The word that is a relative pronoun. Within the relative clause, the relative pronoun stands for the noun phrase it references in the main clause, which is one of the arguments of the verb in the relative clause. In the example, the argument is the house, the direct object of built. A syntactic verb argument, in linguistics, is a phrase that appears in a relationship with the verb in a proposition. ...

Other arguments can be relativised using relative pronouns:

Subject: Simon is the boy who kissed Sandra.

Indirect object: Simon is the boy that Sandra gave a gift to.

Adpositional complement: Jack built the house in which I now live.

Possessor: Simon is the boy whose friend built my house.

Not all languages have relative pronouns. Those that do tend to use words which originally had other functions; for example, the English which is also an interrogative word. This suggests that relative pronouns might be a fairly late development in many languages. In linguistics, an interrogative word is a function word used to introduce an interrogative clause. ...

Relative pronouns may or may not agree with the antecedent. In Spanish, for example, some relative pronouns agree in gender and number with the noun they modify. In English, different pronouns are sometimes used if the antecedent is a human being, as opposed to a non-human or an inanimate object (as in who/that). In some languages, the relative pronoun is an invariable word. In linguistics, grammatical gender is a morphological category associated with the expression of gender through inflection or agreement. ...

See also

• For specific discussion of English usage: English relative clauses or English grammar.
• Relative pronouns in Spanish