Relative pronouns introduce a relative clause that gives more information about a noun or pronoun. They connect the clause to its antecedent, so the listener knows exactly which person, thing, place, or time you mean. In English, relative clauses can be defining meaning needed to identify the noun or non-defining extra information. Choosing the correct relative pronoun depends mainly on what you refer to and the role the pronoun plays inside the relative clause.

The core English relative pronouns are who, whom, whose, which, and that. Who and whom refer to people, which refers to things and sometimes animals, whose shows possession, and that can refer to people or things in defining relative clauses. There are also relative words like where, when, and why that work like relative pronouns for place, time, and reason.

Word/Phrase	Definition	Example
who	Refers to people, often as the subject of the relative clause	The student who sits there is new.
whom	Refers to people as the object in formal style	The person whom I called did not answer.
whose	Shows possession for people, animals, or things	I met a writer whose book won a prize.
which	Refers to things, and can introduce non-defining clauses	The car which I bought is electric.
that	Refers to people or things in defining clauses, common in speech	The movie that we watched was long.
where	Refers to a place meaning in a relative clause	This is the café where we met.
when	Refers to time meaning in a relative clause	I remember the day when we moved.
why	Refers to reason meaning after reason	That is the reason why she left.

Defining relative clauses identify which specific person or thing you mean, so they are essential to the meaning of the sentence. They are not separated by commas. In defining clauses, that is very common, and who or which are also possible depending on the antecedent. If the relative pronoun is the object of the clause, it can often be omitted in defining clauses.

Non-defining relative clauses add extra information that is not needed to identify the noun. They are set off by commas, and in speech they are usually marked by a pause. In non-defining clauses, you generally use who, whom, whose, or which, and you do not use that. You also do not omit the relative pronoun in non-defining clauses.

Rule	Example
Use commas for non-defining relative clauses	My sister, who lives in Rome, is visiting.
Do not use that in non-defining clauses	The report, which was confidential, leaked.
Keep the relative pronoun in non-defining clauses	The museum, which we visited yesterday, was crowded.

The relative pronoun can function as the subject or the object inside the relative clause. If it is the subject, it cannot be omitted. If it is the object, it is often omitted in defining clauses, especially in speech and informal writing. Understanding the pronoun’s role helps you choose between who and whom and helps you decide whether omission is possible.

Rule	Example
Subject relative pronoun cannot be omitted	The woman who called left a message.
Object relative pronoun can be omitted in defining clauses	The woman I called left a message.
Test: replace the pronoun with he she they or him her them in the clause	The man who helped us was kind. The man we thanked was kind.

Who is used when the relative pronoun is the subject of the relative clause, while whom is used when it is the object, especially in formal style. In everyday English, whom is often replaced by who, except after a preposition in careful writing. In very informal speech, many speakers avoid whom entirely and restructure the sentence if needed.

Rule	Example
Use who as the subject in the relative clause	The colleague who sits near me is helpful.
Use whom as the object in formal style	The colleague whom I respect is retiring.
After a preposition, whom is common in formal writing	The professor to whom I wrote replied.
In informal style, who often replaces whom	The person who I met yesterday was friendly.

Whose expresses possession and can refer to people, animals, and things. It links the antecedent to something that belongs to it, such as a body part, family member, property, or feature. Whose works in both defining and non-defining clauses and is often the most natural choice even when referring to things. It is followed by a noun phrase, not a complete clause.

That and which can both refer to things in defining relative clauses, but their distribution differs by style and punctuation. In American English, many writers prefer that for defining clauses and which for non-defining clauses. In British English, which is common in defining clauses as well, especially in more formal writing. Regardless of variety, which is the normal choice for non-defining clauses, and that is not used there.

Region	Word	Regional Definition
🇺🇸American English	that	Commonly preferred for defining clauses about things
🇺🇸American English	which	Commonly preferred for non-defining clauses about things
🇬🇧British English	which	Often used in defining clauses as well as non-defining clauses
General	that	Not used in non-defining clauses

With relative clauses, prepositions can appear at the end of the clause or before the relative pronoun. End-position prepositions are common and natural in conversation. Fronted prepositions are more formal and usually require whom for people and which for things. If the preposition is fronted, you cannot omit the relative pronoun.

Rule	Example
Common: preposition at the end	The chair that I sat on was broken.
Formal: preposition before the relative pronoun	The chair on which I sat was broken.
Formal with people often uses whom	The client for whom we worked was satisfied.
If the preposition is fronted, do not omit the pronoun	The topic about which we spoke was sensitive.

Where, when, and why introduce relative clauses with meanings of place, time, and reason. They often replace patterns like in which, on which, or for which, and they are especially common in speech and general writing. They are most natural after nouns like place, day, time, and reason. In many cases, why can be omitted after reason without changing the meaning.

Rule	Example
Use where after place nouns	This is the house where I grew up.
Use when after time nouns	I will never forget the moment when she arrived.
Use why after reason, often optional	That is the reason she left.
More formal alternatives use preposition plus which	This is the house in which I grew up.