Relative pronouns connect a main clause to a relative clause. They refer back to a noun or pronoun called the antecedent. English commonly uses 'who', 'whom', 'whose', 'which', and 'that' as relative pronouns. Choosing the right pronoun depends on whether the antecedent is a person or a thing, and on the grammatical role inside the relative clause.

'Who' is a relative pronoun used for people as the subject of a relative clause. It introduces information about a person or people and performs the action in the relative clause. Use 'who' when the relative clause describes or identifies a person and acts as the subject inside that clause.

Word/Phrase	Definition
who	A relative pronoun for people as the subject of a relative clause.

'Whom' is a relative pronoun used for people as the object of a relative clause. It refers to a person who receives the action inside the relative clause. In modern English, 'whom' is formal and often replaced by 'who' or omitted in speech, but it remains correct when the pronoun is an object.

Word/Phrase	Definition
whom	A relative pronoun for people as the object of a relative clause.

'Whose' is a relative pronoun that shows possession in a relative clause. It can refer to people or, in formal writing, to animals or things when indicating ownership or association. The noun following 'whose' is what is possessed or related.

Word/Phrase	Definition
whose	A relative pronoun that shows possession in a relative clause.

'Which' is a relative pronoun used for things, animals, or groups as the subject or object of a relative clause. It often appears in non-restrictive clauses, which add extra information and are usually marked by commas. Use 'which' when the antecedent is not a person and the clause identifies or describes it.

Word/Phrase	Definition
which	A relative pronoun for things or animals as subject or object in a relative clause.

'That' is a relative pronoun used for people or things in restrictive relative clauses. Restrictive clauses define or identify the noun and are not set off by commas. Use 'that' when the clause is essential to the meaning of the sentence, especially with things, and often with groups or categories.

Word/Phrase	Definition
that	A relative pronoun for people or things in restrictive relative clauses.

Restrictive relative clauses give essential information to identify the noun and usually use 'that' or 'who' without commas. Non-restrictive relative clauses give extra information and usually use 'which' or 'who' with commas. The choice between restrictive and non-restrictive changes the meaning and punctuation, not just the pronoun.

Rule
Restrictive clauses give essential information and do not use commas.
Non-restrictive clauses give extra information and use commas.

Use 'who' and 'whom' for people and 'which' for things or animals. Use 'whose' for possession, usually with people, and sometimes with things in formal contexts. Use 'that' for people or things in restrictive clauses when the information is necessary.

Rule
Use 'who' for people as subject and 'which' for things.
Use 'whom' for people as object, especially in formal writing.
Use 'that' for essential information with people or things.

The relative pronoun can be omitted when it refers to the object of the relative clause. This omission is common in speech and informal writing with restrictive clauses. Do not omit the pronoun when it is the subject of the relative clause.

Rule
The relative pronoun can be omitted when it is the object in a restrictive clause.
The relative pronoun cannot be omitted when it is the subject of the relative clause.