Grammar Relative Clauses LexFizz Team 12 min read
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Practise relative clauses with Cloze Dropdown exercises. Also see English Clauses Guide and Relative Clauses Practice.

Key Takeaways
  • Who refers to people; which refers to things and animals; that can refer to both people and things in defining clauses.
  • Defining relative clauses identify which person or thing you mean — no commas.
  • Non-defining relative clauses add extra information — commas required, and that cannot be used.
  • Whose shows possession for both people and things.
  • The relative pronoun can often be omitted in defining clauses where it is the object of the verb.

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Relative pronouns are small but powerful words that connect clauses and give your English a more sophisticated, natural flow. Without them, you would have to use short, choppy sentences. With them, you can pack more information into a single, elegant sentence. This guide covers every relative pronoun in English — who, which, that, whose, whom — explains the crucial distinction between defining and non-defining relative clauses, and addresses the most common mistakes learners make.

What Are Relative Pronouns?

A relative pronoun introduces a relative clause — a clause that gives more information about a noun (the antecedent) in the main sentence. The relative pronoun connects the two clauses and refers back to the antecedent.

The doctor who treated me was very kind. (who = the doctor)

The book that I borrowed was fascinating. (that = the book)

The company, which was founded in 1990, is now expanding. (which = the company)

English relative pronouns are: who, whom, whose, which, and that. The choice depends on whether the antecedent is a person or a thing, and whether the clause is defining or non-defining.

Who vs. Which vs. That

The most fundamental rule is:

  • who (and whom) → refers to people
  • which → refers to things and animals
  • that → can refer to both people and things, but only in defining clauses

Examples

The woman who called you left a message. (person)

The phone that rang was mine. (thing, defining)

The report, which was 50 pages long, took three weeks to write. (thing, non-defining)

The woman which called you left a message. (wrong: which cannot refer to a person)

The report, that was 50 pages long, took three weeks to write. (wrong: that cannot be used in non-defining clauses)

Pro tip: In everyday informal English, “that” is commonly used instead of “who” for people in defining clauses (“The man that called”). This is widely accepted. However, in formal writing, use “who” for people.

Defining Relative Clauses

A defining (restrictive) relative clause identifies which specific person or thing you are talking about. Without it, the sentence loses its essential meaning. Defining clauses have no commas.

Structure and Examples

The student [who passed the exam] received a certificate.

Remove the relative clause and you get: “The student received a certificate.” Which student? We do not know. The clause defines which student, so it is essential.

The car that broke down on the motorway was towed away.

The colleague who helped me is called Priya.

The hotel which / that we stayed in was excellent.

Non-Defining Relative Clauses

A non-defining (non-restrictive) relative clause adds extra, non-essential information about a noun that is already clearly identified. These clauses are enclosed in commas (or dashes in informal writing). Remove the clause and the main sentence still makes complete sense.

Key rules for non-defining clauses:

  • Always use commas before and after the clause.
  • Use who for people, which for things. Never use that.
  • The relative pronoun cannot be omitted.

Examples

My sister, who lives in Edinburgh, is visiting next week.

The Eiffel Tower, which was built in 1889, receives millions of visitors each year.

My sister, that lives in Edinburgh, is visiting next week. (wrong: that in non-defining clause)

The Eiffel Tower, built in 1889, receives millions of visitors each year. (the pronoun cannot be omitted here)

The comma test: if you can remove the clause and the sentence still makes sense and refers to the same specific thing, it is non-defining — use commas. If removing the clause changes which person/thing you mean, it is defining — no commas.

Whose

Whose is the possessive relative pronoun. It replaces possessive determiners (his, her, its, their) within a relative clause and can be used for both people and things.

Using Whose

The author whose book I read last week is speaking tonight. (= her book)

The company whose logo I designed has just won an award. (= its logo)

We need someone whose skills match the job description.

Note: whose is always followed directly by a noun, unlike who and which which are followed by a verb or subject.

Whom

Whom is the object form of who. It is used when the relative pronoun is the object of the verb or preposition in the relative clause, not the subject. In formal written English, whom is preferred; in spoken English, who is commonly used instead.

When to Use Whom

The manager whom I spoke to was very helpful. (formal: I spoke to him)

The manager who I spoke to was very helpful. (informal, also acceptable)

The candidate whom we selected has extensive experience.

Quick test: If you can replace the relative pronoun with “him/her/them” (objective case), use whom. If you can replace it with “he/she/they” (subjective case), use who.

The person who called… → “he/she called” → who ✓

The person whom we called… → “we called him/her” → whom ✓

Omitting the Relative Pronoun

In defining relative clauses, the relative pronoun can be omitted when it functions as the object of the verb in the relative clause (not the subject). This is sometimes called a contact clause and is very common in spoken English.

When You Can Omit the Pronoun

The film [that] we watched last night was brilliant. (object: we watched it)

The person [who] you need to speak to is in room 3. (object: you need to speak to them)

When You Cannot Omit the Pronoun

The man who called yesterday left a message. (subject: he called — cannot omit)

The report, which was 50 pages, took three weeks. (non-defining — cannot omit)

Common Mistakes with Relative Pronouns

Mistake 1: Using “that” in a non-defining clause

London, that is the capital of England, has a population of over 9 million.

London, which is the capital of England, has a population of over 9 million.

Mistake 2: Forgetting commas in non-defining clauses

My father who is 70 years old still runs marathons. (implies he has more than one father)

My father, who is 70 years old, still runs marathons.

Mistake 3: Double subject (adding a pronoun after the relative pronoun)

The woman who she works in reception is called Maria.

The woman who works in reception is called Maria.

Mistake 4: Using “which” for people

The teacher which gave us the assignment is excellent.

The teacher who gave us the assignment is excellent.

Relative Pronoun Reference Table

PronounRefers toClause typeCan be omitted?
whoPeopleDefining & non-definingOnly if object (defining only)
whomPeople (object)Defining & non-definingOnly if object (defining only)
whichThings & animalsDefining & non-definingOnly if object (defining only)
thatPeople & thingsDefining onlyOnly if object
whosePeople & things (possessive)Defining & non-definingNo

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Frequently Asked Questions

What is the difference between who and which in English?
Who refers to people: “The man who called”. Which refers to things and animals: “The book which I read”. Using which for people (“the woman which…”) is a common learner error and is considered incorrect in standard English. In defining clauses, both who (for people) and which (for things) can be replaced by that.
Can I use “that” instead of “who” in English?
Yes, in defining relative clauses only. “The student that passed” is grammatically correct and widely used in informal English. However, in formal writing, “who” is preferred for people. That can never be used in non-defining relative clauses (those with commas): “My sister, who lives in Paris” — not “my sister, that lives in Paris.”
What is the difference between defining and non-defining relative clauses?
A defining clause identifies which specific person or thing you mean and is essential to the meaning of the sentence — no commas. A non-defining clause adds extra information about something already identified — always use commas. Compare: “The book that I recommended” (which book? the one I recommended — defining) vs. “The book, which I recommended to everyone, is now a film” (we already know which book; the clause adds extra info — non-defining).
When do I use “whose” vs. “who’s”?
These two words sound the same but have completely different functions. Whose is the possessive relative pronoun: “the woman whose bag was stolen.” Who’s is a contraction of “who is” or “who has”: “Who’s calling?” (= Who is calling?). A simple test: if you can expand it to “who is” or “who has,” use who’s. If it shows possession, use whose.
Can “whose” be used for things (not just people)?
Yes. Whose is used for both people and things when showing possession: “a country whose economy is growing”, “a company whose products are sold worldwide.” In formal writing, “of which” can also be used for things (“a company the products of which are sold worldwide”), but this is awkward and rarely used in modern English. Whose is the natural, accepted choice.
When can I omit the relative pronoun?
You can omit the relative pronoun in a defining clause when it is the object of the verb in the relative clause. Test this by checking if the relative clause already has its own subject and verb: “The film [that] we watched” — “we” is the subject of “watched,” so the pronoun can be dropped. You cannot omit it when it is the subject: “The film that won the award” — “that” is the subject of “won.”
Is “whom” still used in modern English?
Whom is still used in formal written English and is considered correct. In spoken English and informal writing, most native speakers use who even in object positions (“the person who I spoke to”). You will not be wrong to use who informally, but knowing whom is important for formal writing, academic English, IELTS, and professional communication.
Why do I need commas in non-defining relative clauses?
Commas signal to the reader that the information in the clause is extra, non-essential context — it adds detail but does not change which specific person or thing you are referring to. Without commas, the clause reads as defining, which can change the meaning. “My brother who lives in Paris is a chef” (implies I have more than one brother) vs. “My brother, who lives in Paris, is a chef” (I have one brother, and he lives in Paris).
What is a double subject error with relative pronouns?
A double subject error occurs when a learner adds a personal pronoun after the relative pronoun, creating two subjects: “The doctor who he treated me” is wrong because “who” already functions as the subject. The correct form is simply “The doctor who treated me.” This error is common among speakers of languages where the relative clause structure differs from English.
What is the difference between “the book which” and “the book that”?
In a defining relative clause, both are correct and interchangeable: “the book which I read” and “the book that I read” mean the same thing. American English tends to prefer that for defining clauses and reserves which for non-defining clauses. British English accepts both in defining clauses. In non-defining clauses, only which is correct: “the book, which I read on holiday, was brilliant.”