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Advanced Relative Clauses

1 min
C1

Use a defining relative clause (no commas) when the clause is essential to identify which person or thing you mean, a non-defining relative clause (with commas) when it just adds extra, removable information, and a reduced relative clause (dropping the pronoun) to compress either type into a shorter phrase.

CEFR C1·clauses

Formula

(no comma)
(with commas)
: adds extra information

Examples

Positive
The book which I recommended is a bestseller.
Negative
Not applicable
Question
The architect whose designs won awards is coming to speak.

Usage

  • •Providing essential information to identify nouns
  • •Adding non-essential additional information
  • •Reducing clauses to more concise forms

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Defining vs non-defining relative clauses — what's the difference?

The comma carries real meaning. Without commas, a relative clause restricts the noun — it tells you which one: "The students who passed the exam were given certificates" (only the ones who passed). With commas, the clause just adds extra, removable information: "The report, which took three months to write, was finally published" (the report is already identified; the clause is a bonus fact).

"That" is only for defining clauses and is never used in non-defining ones: "My brother, that lives in Paris" is wrong — use "My brother, who lives in Paris."

How do you form a reduced relative clause?

Drop the relative pronoun and the "to be" verb, and use a participle instead: active meaning takes the present participle ("the man running" = the man who is running), passive meaning takes the past participle ("the letter written yesterday" = the letter that was written yesterday).

Reduced relatives let you compress a full clause into a tight phrase, which is why they show up constantly in native-like academic and journalistic prose ("the report submitted last week").

Comparison Table

Defining, non-defining, and reduced relative clauses compared
FormCommasCan use "that"Removable without changing meaningExample
DefiningNoYesNo — removing it changes who/what is meantThe book which I recommended is a bestseller.
Non-definingYes, requiredNo — use who/whichYes — it only adds extra informationThe report, which took three months to write, was finally published.
ReducedNoN/A — no pronoun at allDepends on the source clauseThe woman standing at the door is my manager.
Save this comparison chart
Comparison diagram: Defining, non-defining, and reduced relative clauses comparedDownload PNG

More Examples

  • The students who passed the exam were given certificates.

    Defining: only those who passed (no commas)

  • The report, which took three months to write, was finally published.

    Non-defining: extra info, removable

  • The woman standing at the door is my manager.

    Reduced relative clause (who is standing → standing)

Common Mistakes

  • ✗❌ Using "that" in non-defining clauses: "My brother, that lives in Paris, …" → ✓ "…, who lives in Paris, …"
  • ✗❌ Missing commas in non-defining clauses: "My car which cost a fortune broke down" → ✓ "My car, which cost a fortune, broke down"
  • ✗❌ Reduced relative with the wrong participle: "The letter writing yesterday" → ✓ "The letter written yesterday" (passive = past participle)

Tips

  • ✓Defining clauses: no commas, can use "that". Non-defining: commas required, never use "that".
  • ✓Reduced relatives: active → present participle (the man running), passive → past participle (the letter written).

Advanced Notes

The comma distinction carries real meaning and is a common editing error even among advanced writers — remove the commas and the clause now restricts the noun; add them and it merely adds parenthetical information. "Whom" (object) is technically correct but sounds formal; "who" is widely accepted in speech. Reduced relatives allow elegant compression ("the report submitted last week") that characterises native-like academic prose. The sentential relative ("He ignored me, which upset her") comments on a whole clause, not a noun — a subtlety often missed at C1.

FAQ

Can you use "that" in a non-defining relative clause?

No. "My brother, that lives in Paris, …" is wrong — non-defining clauses (the ones with commas) always use "who," "which," or "whose," never "that."

Do non-defining relative clauses need commas?

Yes, always. "My car which cost a fortune broke down" is missing them — it should be "My car, which cost a fortune, broke down." Without the commas, the clause reads as if it were identifying which car, which changes the meaning.

Reduced relative clause: present or past participle?

Match the voice of the original clause. Active meaning (the subject does the action) takes the present participle: "the letter writing yesterday" is wrong — it should be "the man writing the letter." Passive meaning (the action is done to the noun) takes the past participle: "the letter written yesterday."

What's the difference between a relative clause and a participle clause?

A relative clause keeps the relative pronoun and a finite verb ("the man who was running"). A participle clause drops both and uses the -ing or -ed form directly ("the man running") — it's essentially a reduced relative clause, expressing the same idea in a more compressed form.

Is "whom" still used in English?

Yes, but mainly in formal writing. "Whom" is technically correct for the object of a verb or preposition ("the architect whom we hired"), but "who" is widely accepted in speech and informal writing even in object position.

Practice

  1. 1.The students passed the exam were given certificates.
  2. 2.My car, cost a fortune, broke down.
  3. 3.The letter yesterday arrived late.
  4. 4.The man at the door is my manager.
  5. 5.My brother, lives in Paris, is visiting next week.
Quiz loads as you scroll…

Compare With

Participle Clauses(B2)Substitution and Ellipsis(C1)Relative Clauses (Defining)(B1)