Relative Pronouns (Who, Which, That): English Grammar Guide

Relative pronouns are an essential part of English grammar because they help connect ideas smoothly and clearly. Words like who, which, and that allow us to combine sentences, describe nouns in more detail, and avoid unnecessary repetition. In this guide, we’ll explore what relative pronouns are, how to use them correctly, and how they make your sentences more natural and fluent.

What Are Relative Pronouns?

Relative pronouns are words that introduce relative clauses — parts of a sentence that describe or give more information about a noun. They connect two ideas: the main clause and the relative clause.

For example:

• The man who lives next door is a teacher.
  Here, “who lives next door” is a relative clause describing “the man.”

Common relative pronouns include:

• who – for people

• which – for animals or things

• that – for people, animals, or things (in informal use)

The Function of Relative Pronouns

Relative pronouns act as a bridge between two clauses. They also serve as the subject or object of the relative clause.

Example 1 (subject):

• I met a woman who speaks five languages.
  → “Who” is the subject of the verb “speaks.”

Example 2 (object):

• The book that I read was fascinating.
  → “That” is the object of the verb “read.”

Without relative pronouns, you would need to write two separate sentences:

• I met a woman. She speaks five languages.
  Using a relative pronoun makes the sentence smoother and more natural.

Using “Who”

Who refers only to people and can act as both subject and object in a sentence.

Examples:

• The teacher who helped me was very kind. (subject)

• The person who you called is not available. (object)

When “who” is the object of the clause, it’s common in spoken English to omit it:

• The person (who) you called is not available.

More Examples:

• Students who study hard often succeed.

• She met the doctor who treated her last year.

• Anyone who wants to join the club must apply by Friday.

Common Mistake:

❌ The car who is parked outside is mine.
✅ The car which is parked outside is mine.

“Who” cannot refer to things — only to people.

Using “Which”

Which refers to animals or things, not people. It can describe objects, ideas, or entire clauses.

Examples:

• The phone which I bought last week is already broken.

• The movie which we watched was amazing.

• I forgot my umbrella, which was a big mistake.

In the last example, “which” refers to the whole previous idea (forgetting the umbrella), not just one word.

Omitting “Which”

Unlike “that,” “which” is not usually omitted, especially in formal writing.
❌ The phone I bought last week is already broken. → (informal)
✅ The phone which I bought last week is already broken. → (formal)

Using “That”

That can refer to people, animals, or things. It is more informal and flexible than “who” or “which.” In everyday English, “that” is often used instead of “who” or “which.”

Examples:

• The man that helped me is my uncle.

• The movie that won the award is fantastic.

• This is the book that I told you about.

Omitting “That”

When “that” is the object of the relative clause, it can be left out:

• The book (that) I borrowed was interesting.

• The song (that) you love is playing on the radio.

However, when it is the subject, it cannot be omitted:

• ✅ The man that called you is waiting.

• ❌ The man called you is waiting.

Defining vs. Non-Defining Relative Clauses

Relative clauses come in two main types: defining and non-defining. Understanding the difference is crucial for correct punctuation and clarity.

1. Defining Relative Clauses

These identify exactly which person or thing you mean. Without the clause, the sentence loses its meaning.
No commas are used.

Examples:

• The students who arrived early got the best seats.

• The book that I borrowed from you was helpful.

(We need these clauses to know which students or book we’re talking about.)

2. Non-Defining Relative Clauses

These add extra information, not essential to understanding the main point.
They are always set off by commas, and you cannot use “that” in this type.

Examples:

• My brother, who lives in Canada, is visiting next week.

• The Eiffel Tower, which is in Paris, is very famous.

If we remove the clause, the main meaning remains:

• My brother is visiting next week.

Who vs. That vs. Which — Quick Comparison

Advanced Notes

1. “Whose” – The Possessive Form

While not part of the main three, whose is another important relative pronoun.
It shows possession for both people and things.

Examples:

• The man whose car was stolen went to the police.

• The company whose logo changed is Apple.

2. “Where” and “When”

These are also relative words but act as relative adverbs.

Examples:

• The city where I was born is beautiful.

• The day when we met was unforgettable.

They work like relative pronouns by connecting clauses, but they describe places or times.

3. Formal vs. Informal Choices

In formal English, “who” and “which” are preferred.
In spoken or informal English, “that” is more common:

• Formal: The book which you recommended was excellent.

• Informal: The book that you recommended was excellent.

Common Errors and How to Avoid Them

1. Using “which” for people
   ❌ The woman which works here is nice.
   ✅ The woman who works here is nice.

2. Using commas in defining clauses
   ❌ The students, who arrived early, got the best seats.
   ✅ The students who arrived early got the best seats.

3. Using “that” in non-defining clauses
   ❌ My house, that is near the beach, is for sale.
   ✅ My house, which is near the beach, is for sale.

4. Omitting the pronoun when it’s the subject
   ❌ The man called you is my father.
   ✅ The man who called you is my father.

Practice Sentences

Try completing these with the correct relative pronoun:

1. The person ___ called you is my friend.

2. The movie ___ we watched last night was amazing.

3. This is the hotel ___ I told you about.

4. My sister, ___ lives in Tokyo, is visiting soon.

5. The car ___ was parked outside belongs to my neighbor.

Answers:

1. who / that

2. which / that

3. that / which

4. who

5. which / that

Why Relative Pronouns Matter

Relative pronouns make writing and speech more fluent and descriptive. They allow you to combine ideas naturally, avoid repetition, and sound more like a native English speaker. Mastering “who,” “which,” and “that” helps you:

• Write complex sentences confidently

• Improve reading comprehension

• Speak more precisely

For example, instead of saying:

“I have a friend. He lives in Japan.”

You can say:

“I have a friend who lives in Japan.”

It’s smoother, more natural, and stylistically advanced.

Conclusion

Relative pronouns — who, which, and that — are powerful tools for connecting ideas and describing nouns clearly.

• Use who for people.

• Use which for things and animals.

• Use that for people or things, especially in defining clauses.

Remember to avoid “that” in non-defining clauses and use commas when adding extra information.
With consistent practice, you’ll find that relative clauses make your English not only grammatically correct but also richer and more elegant.

What is a relative pronoun and why is it used?

A relative pronoun introduces a relative clause that modifies a noun or pronoun, linking two ideas into a single sentence. In English, the most common relative pronouns are who, which, and that. They help reduce repetition, add precision, and improve sentence flow. For example, “The scientist who won the award” uses a relative clause to identify which scientist is meant.

When should I use who instead of that or which?

Use who to refer to people. It can function as the subject (“The tutor who explains clearly…”) or the object (“The colleague who you recommended…”). In everyday speech, some speakers use that for people in defining clauses, but who is clearer and preferred in careful or formal writing.

When should I use which?

Use which for animals and things, especially in non-defining clauses (with commas) or when the antecedent is a whole idea. Example: “She missed the deadline, which surprised her manager.” Here, which refers to the entire preceding clause (“missed the deadline”).

When is that the best choice?

That is common in defining (restrictive) clauses and can refer to people, animals, or things: “The policy that we adopted improved retention.” It is concise and frequent in speech and neutral writing, but avoid that in non-defining clauses (with commas), where which is required.

What is the difference between defining and non-defining relative clauses?

A defining (restrictive) clause specifies exactly which person or thing you mean; no commas are used: “Students who submit early get feedback.” A non-defining (non-restrictive) clause adds extra, non-essential information and is set off by commas: “My advisor, who is on sabbatical, will return in June.” Removing a defining clause often changes meaning; removing a non-defining clause doesn’t.

Can I omit the relative pronoun?

Yes, when the pronoun is the object of the relative clause in a defining clause: “The book (that/which) I borrowed was excellent.” Do not omit the pronoun when it is the subject: “The book that won the prize…” (You cannot say “The book won the prize…”, because the clause needs its subject.) Omission is most natural with that in informal styles.

Is it okay to use that with people?

Yes, in defining clauses many writers and speakers use that for people: “The engineer that led the project…” However, some style guides prefer who for people, especially in formal or respectful contexts. In non-defining clauses, do not use that; use who or which as appropriate.

Should I use commas with which?

Use commas with which in non-defining clauses: “The mural, which took months to complete, draws tourists.” In American English, many editors encourage that (no commas) for defining clauses and which (with commas) for non-defining clauses. British English is more flexible, but clarity should guide your choice.

What is the possessive relative pronoun whose and when do I use it?

Whose expresses possession for people, animals, and even things: “The researcher whose article you cited…,” “A firm whose products are recyclable…” Although some hesitate to use whose for things, it is widely accepted and often more elegant than awkward alternatives like “of which.”

How do I choose between which and “of which”?

Use which directly when it fits naturally: “The report, which was published in May…” Use “of which” for possessive-like relationships, especially in formal writing: “A study, the results of which were inconclusive…” In many cases, whose sounds smoother: “A study whose results were inconclusive…”

Can relative pronouns refer to entire ideas or only to nouns?

They usually modify a specific noun (the antecedent). However, which in a non-defining clause can refer to a preceding clause or idea: “He forgot his passport, which caused a delay.” Ensure the reference is unambiguous; otherwise, rephrase to avoid confusion.

What are common mistakes with relative pronouns?

• Using which for people: “The manager who approved it,” not “which approved it.”
• Using that in non-defining clauses: “My car, which I bought last year,…” not “that.”
• Dropping a subject pronoun: “The artist who painted this…” not “The artist painted this…”
• Mismatched number or person: Ensure verb agreement with the pronoun’s function in the clause.

How do relative pronouns affect subject–verb agreement?

The verb in the relative clause agrees with the antecedent and the pronoun’s role as subject or object. Example: “The data that are missing…” in formal scientific style (treating data as plural). In general usage, treat the antecedent as it is commonly used in your field, and keep the clause consistent: “The team that is winning,” not “that are winning.”

Can I start a sentence with a relative clause?

You cannot begin with a bare relative pronoun without its antecedent (“Which was surprising.”) unless the antecedent appears earlier or the structure is recast. Instead, use a full sentence or a participial phrase: “He missed the flight, which was surprising,” or “Surprisingly, he missed the flight.”

What is the difference between who and whom in relative clauses?

Who is the subject; whom is the object: “The mentor whom I consulted…” In modern English, whom is often replaced by who in speech, especially when not preceded by a preposition. With a preposition, formal writing prefers “the professor to whom I wrote” over “the professor who I wrote to.”

Where do prepositions go in relative clauses?

In formal style, place the preposition before the relative pronoun: “The client for whom I prepared the brief.” In neutral or informal style, stranding the preposition is natural: “The client who I prepared the brief for.” Avoid mixing forms in the same document; pick a tone and be consistent.

How do I avoid ambiguous antecedents?

Place the relative clause as close as possible to the noun it modifies and choose the pronoun that makes the relationship obvious. If a clause might seem to modify the wrong noun or the whole sentence unintentionally, rephrase: “We approved the plan for the new wing, which will increase capacity,” could be clearer as “We approved the plan to increase capacity for the new wing.”

Are there register (formality) preferences among who, which, and that?

Yes. In formal writing, use who for people and which for things, reserving that mainly for defining clauses. In conversational or journalistic prose, that is common and succinct in restrictive contexts. Always avoid that in non-defining clauses.

Can relative pronouns appear after quantifiers like “all,” “many,” or “most”?

Yes. Structures such as “all of whom,” “most of which,” and “many of which” are idiomatic, especially in non-defining clauses: “Twenty students enrolled, most of whom are international.” These phrases provide compact, high-information summaries.

What about relative adverbs like where, when, and why—are they interchangeable with pronouns?

They function similarly but modify places, times, and reasons rather than nouns directly: “the city where I grew up,” “the year when we met,” “the reason why I left.” You can often rephrase with which + preposition: “the city in which I grew up.” Choose the version that is clearest and fits the tone.

How can I test whether a clause is defining or non-defining?

1. Remove the clause. If the reference becomes vague or changes meaning, it is defining.
2. Check punctuation. Non-defining clauses require commas; defining clauses do not.
3. Try substituting that. If it works and no commas are needed, the clause is likely defining (though style may still prefer who/which).

What revision strategies improve clarity with relative clauses?

• Minimize stacking: Avoid long chains of nested clauses; split into two sentences when readability suffers.
• Prefer proximity: Keep the relative clause close to its antecedent.
• Choose the right marker: Use who for people, which for things, that for concise defining clauses.
• Trim objects: Omit the pronoun when it is the object in a defining clause, if the rhythm improves.

Can I use relative clauses to vary sentence rhythm and style?

Yes. Relative clauses let you balance short, direct sentences with richer, more nuanced ones. In persuasive and academic writing, alternating simple sentences with carefully placed relative clauses creates emphasis, attributes evidence, and shows relationships between ideas without overloading the reader.

Quick practice: which relative pronoun fits best?

Choose the best option and then compare to the key below.

1. The analyst ___ wrote the memo clarified the risks.
2. The framework ___ we adopted reduced defects.
3. Her proposal, ___ included a pilot test, gained approval.
4. Applicants ___ meet the criteria will be shortlisted.
5. The shipment ___ arrived yesterday contained prototypes.

Key: 1) who/that (subject) 2) that/which or Ø (object) 3) which (non-defining) 4) who/that (defining) 5) which/that (subject).

Final takeaway

Use who for people, which for things (especially in non-defining clauses), and that for concise defining clauses with people or things. Keep relative clauses close to their antecedents, avoid that in non-defining clauses, and omit the pronoun only when it is the object in a defining clause. Prioritize clarity, consistency, and reader comfort in every choice.

English Grammar Guide: Complete Rules, Examples, and Tips for All Levels