Relative Clauses: Who, Which, That & Whose Explained

Reviewed by the Grammarlyzer Editorial Team · Our Review Standards · Published January 29, 2026 · Updated June 13, 2026

Master Defining and Non-Defining Relative Clauses

📌 Quick Answer
Use who for people, which for things, and that for both (in defining clauses only). Use whose to show possession. Defining clauses have no commas and are essential. Non-defining clauses have commas and add optional extra information.

Memory Trick: If you can remove the clause and the sentence still makes sense about the right person/thing, add commas (non-defining). If removing it makes the meaning unclear, no commas (defining).

💡 Key Rule

"That" is only used in defining relative clauses. You can never use "that" after a comma in a non-defining clause.

Quick Comparison

Pronoun Used For Clause Type Example
Who People Defining & Non-defining "The nurse who treated me was brilliant."
Which Things & Animals Defining & Non-defining "The report, which took a month, was excellent."
That People & Things Defining only (no commas) "The book that I recommended is sold out."
Whose People & Things (possession) Defining & Non-defining "The student whose essay won is in my class."

Common Mistakes

Using "Which" for People

❌ Incorrect:

"The manager which approved the budget has resigned."

✓ Correct:

"The manager who approved the budget has resigned."

"Which" is for things, not people. Always use "who" (or "that" in defining clauses) when referring to a person.

Using "That" After a Comma

❌ Incorrect:

"My car, that I bought last year, is already broken."

✓ Correct:

"My car, which I bought last year, is already broken."

"That" cannot appear in non-defining clauses (those with commas). Use "which" for things and "who" for people in non-defining clauses.

Missing Commas in Non-Defining Clauses

❌ Incorrect:

"My sister who is a doctor lives in Toronto."

(Implies you have multiple sisters and this one is the doctor)

✓ Correct:

"My sister, who is a doctor, lives in Toronto."

(Adds extra info — you have one sister and she happens to be a doctor)

Commas change the meaning. Adding or removing commas can imply you have one sibling or several. Always use commas for non-essential information.

When You Can Drop the Relative Pronoun

In everyday writing you often see relative clauses with no "that," "which," or "who" at all. This isn't an error — English lets you omit the pronoun when it is the object of the clause, but not when it is the subject.

Object position: dropping it is fine

"The book that I recommended is sold out" → "The book I recommended is sold out." The pronoun stands for the object (I recommended it), so it can vanish. This only works in defining clauses with no commas.

Subject position: you must keep it

❌ Incorrect:

"The author wrote this lives nearby."

✓ Correct:

"The author who wrote this lives nearby."

Here the pronoun is the subject of "wrote," so dropping it leaves the sentence broken. Quick test: if a verb comes right after the gap, keep the pronoun.

Relative Adverbs: where, when, and why

Clauses about places, times, and reasons often use a relative adverb instead of a pronoun — and it usually reads more smoothly than a "preposition + which" version.

Refers to Word Example
A place where The café where we met has closed. (= in which)
A time when I remember the day when it snowed in May. (= on which)
A reason why That's the reason why she left. (= for which)

Putting a Preposition Before the Pronoun

Formal vs natural word order

In formal writing the preposition can move in front of the pronoun: "the colleague to whom I spoke." In everyday English it stays at the end and the pronoun is often dropped: "the colleague I spoke to." Both are correct; the first sounds formal, the second sounds natural.

"Whom" survives mainly after a preposition

You rarely need whom anymore — except right after a preposition, where "to who" sounds wrong: prefer "with whom," "for whom," "to whom." Elsewhere, "who" is widely accepted. See Who vs Whom for the full test.

🎯 Test Your Knowledge

1. "The engineer ____ designed the bridge received an award."

2. "The new law, ____ was passed last month, affects small businesses."

3. "The student ____ project was selected will present at the conference."

4. "This is the building ____ the meeting will be held."

5. "The contract ____ we signed yesterday is binding."

See It Live: Check a Sentence With Our Engine

Try the rule against a real sentence. This widget runs Grammarlyzer's in-browser engine, so nothing you type leaves your device. The starter sentence (“The manager which approved the budget has resigned.”) already contains a slip—edit it or paste your own to watch the engine react.

The correct version is: "The manager who approved the budget has resigned.".

Honest limits: the engine reliably flags the mechanics—spelling, agreement, punctuation—but whether a sentence is clear is a judgment call. Use the relative clauses guidance above to decide if the structure actually serves the reader.

Frequently Asked Questions

What is the difference between "who", "which", and "that"?

"Who" is for people. "Which" is for things and animals. "That" can be used for both, but only in defining clauses (no commas). In non-defining clauses (with commas), only "who" or "which" are acceptable.

What is a defining relative clause?

A defining clause identifies which person or thing you mean — the information is essential and has no commas: "The student who passed will graduate." This tells you which student specifically.

Can I use "that" after a comma?

No. "That" is never used in non-defining clauses (those with commas). Use "who" for people and "which" for things: "My laptop, which I bought last year, is broken." (NOT: "My laptop, that I bought...")

When should I use "whose"?

"Whose" shows possession in a relative clause — it replaces "his/her/their" to link back to the noun. Works for both people and things: "The student whose essay won the prize" / "The company whose shares dropped."

Can I leave out "that" or "which"?

Yes — but only when the pronoun is the object of a defining clause: "the film (that) we watched." If a verb follows the gap, the pronoun is the subject and must stay: "the film that won the award." You can never drop the pronoun in a non-defining (comma) clause.

Should I use "the reason why" or just "the reason"?

Both are acceptable. "The reason why she left" uses the relative adverb why; "the reason she left" drops it. Some editors trim "why" as redundant after "reason," but it is not an error. The same flexibility applies to "the place (where)" and "the day (when)."

Defining Relative Clauses (No Commas)

A defining relative clause identifies which specific person or thing you mean. It is essential — removing it changes the meaning.

Examples

  • "The candidate who interviews best will get the job." (Professional)
  • "The software that crashed yesterday has been updated." (Professional)
  • "Students who submit early receive extra credit." (Academic)
  • "The restaurant that we visited last month has closed." (Casual)
  • "Any employee whose performance improves will be considered for promotion." (Professional)
  • "The theory that Darwin proposed revolutionized biology." (Academic)

Non-Defining Relative Clauses (With Commas)

A non-defining relative clause adds optional extra information about something already clearly identified. Remove it and the core meaning is unchanged.

Examples

  • "Our CEO, who joined in 2020, has transformed the company." (Professional)
  • "The new policy, which was announced last week, affects all departments." (Professional)
  • "Einstein, who was born in Germany, developed the theory of relativity." (Academic)
  • "My laptop, which I bought last year, keeps overheating." (Casual)
  • "The annual report, whose findings were surprising, will be published tomorrow." (Professional)
  • "The Amazon rainforest, which covers 5.5 million km², is critical for global climate." (Academic)

Word Origins & Etymology

A relative clause is introduced by a relative pronoun (who, whom, whose, which, that) and modifies a noun. The term 'relative' comes from Latin 'relativus' (having reference), because these clauses 'relate back' to a noun.

English has two types: restrictive (essential, no commas) and non-restrictive (extra info, with commas). The distinction determines meaning.

🔗 The Connection

Understanding relative clauses unlocks correct usage of who/whom, which/that, and whose — some of the most confused words in English.

Real-World Examples

📏 Restrictive:

The student who scored highest will receive the scholarship.

No commas = essential (identifies which student)
📏 Non-restrictive:

Maria, who scored highest, will receive the scholarship.

Commas = extra info (we already know it's Maria)
💼 Business:

Employees who complete training are eligible for promotion.

Restrictive: only those who complete training
💼 Business:

Our employees, who complete training annually, are eligible for promotion.

Non-restrictive: ALL employees complete training (extra fact)
❌ Mistake:

The manager who, is on vacation, approved it.

Wrong comma placement. Should be: 'The manager, who is on vacation, approved it.'
💡 Key Rule:

Commas completely change the meaning. 'Students who cheat fail' (only cheaters fail). 'Students, who cheat, fail' (all students cheat and fail).

The comma test shows how commas change restrictive → non-restrictive

Why Do People Confuse Them?

The comma makes or breaks the meaning. Without commas, the clause is restrictive (it limits which noun you're talking about). With commas, the clause is non-restrictive (it adds bonus information). Most writers use commas inconsistently, which can change the intended meaning entirely.

Practice with Related Guides

Keep practicing with closely related guides: Which vs That: When to Use Each and Who vs Whom: The Complete Guide.

Related Articles

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