A relative pronoun is a type of pronoun that connects two clauses together to form a more cohesive sentence or clause. In English, the most common relative pronouns are “that, which, who, whom, whose” and can be used in slightly different forms such as “whoever” and “whosoever.” There are two major ways in which a relative pronoun can be used, which are referred to as restrictive and non-restrictive relative clauses. Restrictive relative clauses do not typically have a comma in them, use “that,” and the second clause is necessary to allow for full meaning, while a non-restrictive clause often does have a comma, use “which” or another pronoun, and the second clause is not absolutely necessary.
Use of a relative pronoun is typically intended to connect two clauses together through a pronoun that allows the second clause to refer to the first. In this type of phrase, the pronoun in the second clause refers to the subject or object of the first clause, which is called the antecedent. Each clause connected by a relative pronoun can be written out separately, and in joining them the use of the pronoun allows for clearer understanding by a reader.
This can be seen in a simple sentence like, “Bob built the house that I moved into last week.” Two short statements could express the same idea as, “Bob built the house. I moved into the house last week.” Rather than using two short clauses, however, they can be connected through the use of a relative pronoun that relates the object of one clause to the subject or object of another.
“Bob built the house” is one clause, and has the subject “Bob,” the verb “built,” and the direct object “the house.” In the second clause, “that I moved into last week,” the relative pronoun “that” takes the place of “the house” from the first clause; “the house” is referred to as the antecedent in this phrase. So the second clause then has the subject “I” and the verb phrase “moved into last week” with a direct object of “that” as a relative pronoun.
This is an example of a restrictive relative clause, in which the second clause is necessary for full meaning. While each clause can exist on its own, the purpose of this sentence is to explain that “Bob” built a house the speaker moved into, and without the second clause this meaning is obscured. In contrast to this is a non-restrictive relative clause, in which the second clause only expands upon the first and is not strictly necessary for meaning.
An example of a non-restrictive relative clause is a statement like “I own a cat, which I found in my garage.” While the second clause “which I found in my garage” provides additional information in the sentence, it is not absolutely required. The meaning of the sentence is that the speaker owns a cat, which is conveyed in the first clause. Restrictive clauses use "that" and do not have a comma, while non-restrictive ones use a relative pronoun like "which" or "who" and separate the clauses with a comma. Relative pronouns in English are often differentiated based on whether the subject is human or not, with “who” and “whom” referring to human antecedents while “that” and “which” are used for non-human ones.