Relative Clauses
1. Definition and Rule
A relative clause is a dependent clause that acts like an adjective — it modifies a noun or pronoun that comes before it. Its job is to give additional information about that noun, helping the reader or listener understand exactly which person, thing, or place is meant.
Without relative clauses, writers would produce short, disconnected sentences. Compare:
I bought a new car. It is very fast. → I bought a new car that is very fast.
Relative clauses are introduced either by relative pronouns (who, whom, whose, which, that) or by relative adverbs (where, when, why). The noun the clause modifies is called the antecedent or head noun.
There are two main types:
- Defining (restrictive) relative clauses — identify which noun is meant; essential to the sentence.
- Non-defining (non-restrictive) relative clauses — add extra, non-essential detail about a noun already identified.
2. Form and Structure
Relative Pronouns
WHO — refers to people; used when the relative pronoun is the subject of the clause. It cannot be omitted.
The man who saw me was tall.
WHOM — refers to people; used when the relative pronoun is the object of the clause, or after a preposition. In modern English it is often dropped in defining clauses.
The man whom I met yesterday is a doctor. / The man I met yesterday is a doctor.
WHOSE — shows possession for both people and things; can never be omitted. Structure: whose + noun.
I have a friend whose mother works at a bank.
He is the student whose house was for sale.
WHICH — refers to things; used as subject or object of the clause. When it is the object, it can be omitted in defining clauses.
The book which sits on the table is mine. (subject — cannot omit)
The book which I was reading is fascinating. / The book I was reading is fascinating. (object — can omit)
THAT — refers to both people and things; used only in defining clauses. It is especially common in spoken English. After superlatives and words like everything, anything, nothing, use that rather than which.
She is the best teacher that I've had.
Everything that glitters is not gold.
Relative Adverbs
WHERE — replaces a preposition + which for locations; acts as an adverbial (not the subject). Use it when a place noun is not the subject of the relative clause.
This is the café where we had coffee last year. (where = at which)
WHEN — replaces a preposition + which for time expressions; also acts as an adverbial.
I'll never forget the moment when I saw her. (when = at which)
WHY — used with the noun reason; replaces for which.
The reason why he left is unknown.
Omission of the Relative Pronoun (Zero Relative)
The relative pronoun may be left out only when it is the object of a defining clause. When it is the subject, it must stay.
The film (that / which) I watched last night was excellent. [object — omission allowed]
The man who saw me was tall. [subject — omission NOT allowed]
3. Uses
- To identify or specify which person, thing, or place is meant (defining use).
- To add supplementary, non-essential details about a noun already known to the reader (non-defining use).
- To combine two short sentences into one more fluent and complex sentence.
- To show possession (whose) for both people and things.
- To give information about place (where), time (when), or reason (why) linked to a head noun.
- To create formal written English by placing a preposition before whom or which at the start of the clause.
4. Worked Examples
Defining Relative Clauses
The book that sits on my desk belongs to Sarah. (specifies which book)
Students who complete their homework early can leave class first. (identifies which students)
The house which I purchased from Peter is very old. (identifies which house)
The traveller whose bag was stolen was upset. (possession — whose)
Non-Defining Relative Clauses
My brother, who is a doctor, lives abroad. (extra detail about an already-identified person)
London, which has some fantastic parks, is where I live. (extra detail about a known place)
My colleague, whose sister is a lawyer, works in accounting. (non-defining possessive)
Relative Adverbs in Context
The restaurant where we met was downtown.
The day when we met was cloudy.
The reason why I'm late is traffic.
Formal vs. Informal Preposition Placement
Formal: The man with whom I was talking is a doctor.
Informal: The man I was talking with is a doctor.
5. Common Mistakes to Avoid
Mistake 1 — Wrong pronoun for people vs. things.
✗ The man which lives here is my neighbour.
✓ The man who lives here is my neighbour.
Rule: Use who / whom for people and which / that for things.
Mistake 2 — Repeating the subject or object inside the clause (redundant pronoun).
✗ That's the school that it does lots of music and drama.
✓ That's the school that does lots of music and drama.
Rule: Once a relative pronoun is used, never repeat the noun or pronoun inside the relative clause.
Mistake 3 — Using that in non-defining clauses.
✗ My brother, that is a doctor, lives abroad.
✓ My brother, who is a doctor, lives abroad.
Rule: That is only permitted in defining clauses. In non-defining clauses, use who (people) or which (things).
Mistake 4 — Wrong use of commas (confusing clause types).
✗ Sally is a committee member, who finds it difficult to make decisions. (if defining is intended)
✓ Sally is a committee member who finds it difficult to make decisions.
Rule: No commas in defining clauses; commas are required on both sides in non-defining clauses.
Mistake 5 — Omitting a subject relative pronoun.
✗ The student passed the exam really did well.
✓ The student who passed the exam really did well.
Rule: A relative pronoun functioning as the subject of its clause can never be removed.
Mistake 6 — Placing the relative clause too far from the head noun, causing ambiguity.
✗ He played soft melodies in the attic that the town loved. (does the town love the attic or the melodies?)
✓ In the attic, he played soft melodies that the town loved.
Rule: The relative clause must follow the head noun immediately.
Mistake 7 — Using where / when as a replacement for the subject.
✗ The restaurant where is big serves good food.
✓ The restaurant that is big serves good food.
Rule: Where, when, and why are adverbials. They cannot replace a subject noun — use that or which instead.
6. Key-Point Callout
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Key points to remember: (1) Use who / whom for people and which / that for things. (2) Defining clauses have no commas and can use that; non-defining clauses require commas and cannot use that. (3) A subject relative pronoun can never be omitted; an object relative pronoun may be omitted only in defining clauses. (4) Whose is never omitted and works for both people and things. (5) Where, when, and why are adverbials — they cannot replace a subject; use that or which for subjects. (6) Always place the relative clause immediately after the head noun it modifies.