A relative pronoun is a pronoun that marks a relative clause within a larger sentence. It is called a relative pronoun because it relates the relative (and hence subordinate) clause to the noun that it modifies. In English, the relative pronouns are: who, whom, whose, whosever, whosesoever, which, and, in some treatments, that. In addition, English has various fused relative pronouns, which combine in one word the antecedent and the relative pronoun: what, whatever, whatsoever, whoever, whosoever, whomever, whomsoever, whichever, and whichsoever,
A relative pronoun links two clauses into a single complex clause. It is similar in function to a subordinating conjunction. Unlike a conjunction, however, a relative pronoun stands in place of a noun. Compare:
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 in some analyses.[1] Within the relative clause, the relative pronoun stands for the noun phrase it references in the main clause (its antecedent), and 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.
Other arguments can be relativised using relative pronouns:
In some languages, such as German and Latin, which have gender, number, and noun declensions, the relative pronoun agrees with its antecedent in gender and number, while its case indicates its relationship with the verb in the relative clause. In some other languages, the relative pronoun is an invariable word.
The words used as relative pronouns are often 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. Some languages, such as Welsh, do not have relative pronouns.
In English and German, 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).
With the relative pronouns, sentences (5) and (6) would read like this:
In sentences (7) and (8), the words that and who are the relative pronouns. The word that is used because the bank is a thing; the word who is used because "she" is a person.
In some languages with relative clauses, such as Mandarin Chinese, there are no relative pronouns. In English, the relative pronoun may be optionally omitted, particularly in speech, from a restrictive relative clause — that is, one which contributes to establishing the identity of the antecedent — if the relative pronoun would serve as the object of the verb or of a stranded preposition in the relative clause (as in This is the car I bought = This is the car that I bought or This is the car you heard of = This is the car of which you heard).