Relative pronouns introduce a relative clause, which adds information to a noun. The clause follows the noun it describes and gives the listener or reader more detail about which person, thing, or idea is meant. In the woman who called, the clause who called identifies the woman. If you remove the clause, the sentence still has a noun, but it loses the extra detail that makes it specific. Relative clauses connect closely to Clauses and depend on Pronouns to stand in for the noun inside the clause.

Adding extra information with relative clauses

Idea
A relative clause gives extra information about a noun and makes the meaning more specific.
A relative clause usually comes immediately after the noun it describes.

Use who for people in a relative clause. It can refer to a subject inside the clause: the teacher who lives next door. Here, who stands for the teacher and acts as the subject of lives. It also appears after a person when the clause identifies that person: a man who works at the airport. The noun before who is the person being described, and the clause gives the extra information that narrows the meaning.

Using who for people in relative clauses

Usage	Explanation
Subject reference	Use who when the relative pronoun refers to a person and acts as the subject of the clause.
People in general	Use who to identify a person when the clause gives important information about them.

Use which for things, animals, objects, and ideas. It appears after the noun it refers to and introduces a clause that describes that noun: the book which I borrowed or the plan which failed. In the clause, which can be the subject or the object. English also often uses which for animals when the speaker thinks of them as things or when the form is very formal. In everyday speech, the choice depends on what the noun refers to, not on the kind of clause.

Using which for things and ideas

Usage	Explanation
Objects	Use which to refer to a thing or object in a relative clause.
Ideas and situations	Use which to refer to an idea or situation when the clause adds information about it.

Use that in defining relative clauses for people and things: the girl that won, the car that we bought, the house that I want. It often appears in speech and writing when the clause is needed to identify the noun. That cannot be used in non-defining relative clauses, so it belongs only in clauses that specify exactly which person or thing is meant. It works with both people and objects, which makes it very flexible in everyday English.

Using that in defining relative clauses

Idea
In defining relative clauses, that can refer to people as well as things.
In defining relative clauses, that can refer to things when the information is needed to identify the noun.

Use whose to show possession inside a relative clause. It means that the noun after whose belongs to, or is connected with, the noun before it: the student whose bag was stolen, the company whose offices are closed. The structure is noun + whose + noun + verb. The possessive idea stays inside the clause, so whose links the two nouns without using a separate possessive phrase. It can refer to people, animals, and things.

Showing possession with whose

Usage	Explanation
Owner of a person	Use whose to show that a person owns or is connected to something in the relative clause.
Owner of a thing	Use whose to show possession when the noun is not a person.

Use whom as the object form for people in formal English: the lawyer whom we met, the guests whom she invited. In the relative clause, whom does not do the action. It receives the action of the verb or appears after a preposition. In modern speech, many speakers use who instead of whom, especially after the noun: the lawyer who we met. After a preposition, whom sounds more formal: the person to whom I spoke.

Formal object form for people

Idea
Use whom as the formal object form for a person in very formal English.
In everyday speech, many speakers use who instead of whom.

Defining relative clauses do not use commas. They are needed to identify the noun, so the clause is part of the noun phrase: the woman who sits by the window, the shirt that I ordered. Without the clause, the listener does not know exactly which woman or which shirt is meant. The relative pronoun is part of the identifying structure, so the clause stays tightly connected to the noun.

Punctuation in defining relative clauses

Idea
A defining relative clause does not use commas.
A defining relative clause is needed to identify the noun clearly.

Non-defining relative clauses use commas because they add extra information about a noun that is already clear: My brother, who lives in Canada, is visiting. The sentence already identifies the brother, so the clause gives additional detail. Non-defining clauses do not use that. They normally use who, which, or whose. The commas mark the clause as separate information, not part of the noun’s basic identification.

Punctuation in non defining relative clauses

Idea
A non defining relative clause uses commas around the extra information.
A non defining relative clause does not use that.

In defining relative clauses, the object relative pronoun can be left out when it is not the subject of the clause: the book I bought, the person we called, the house she painted. The noun before the clause is still clear, and the verb in the clause follows directly after it. You cannot leave out the pronoun when it is the subject: the man who called is correct, but not the man called when the meaning is that the man did the calling. The omission is common with everyday speech and writing, especially after Pronouns that act as objects inside Clauses.

Leaving out object relative pronouns

Usage	Explanation
Defining clause object	You can omit the object relative pronoun when it is not the subject of a defining relative clause.
Informal everyday style	Leaving out the object relative pronoun is common in everyday English when the meaning is still clear.