What Is a Relative Clause?
A relative clause is a group of words built around a relative pronoun (who, which, that, whose, or where) that adds information about a noun. The pronoun sits at the start of the clause and links back to the noun it describes, joining two ideas into one sentence.
Take the sentence "The teacher who graded my exam is strict." The clause "who graded my exam" modifies "teacher," and "who" ties the two parts together grammatically. Remove that pronoun and the connection breaks, leaving two disconnected statements.
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Relative clauses belong to a broader category covered in our parts of speech guide, since relative pronouns form a distinct word class. For a wider foundation before tackling defining and non-defining clause rules, start with the main grammar section.
Relative Pronouns: Comparison Table (Who, Which, That, Where, Whose)
Who, which, that, where, and whose cover almost every relative clause on a CEFR exam, and mixing them up is one of the most common ways test-takers lose points. Each pronoun points to a specific type of noun, and the choice between them often signals whether a clause is defining (essential information) or non-defining (extra detail set off by commas).
| Pronoun | Refers to | Defining / Non-defining | Example sentence |
|---|---|---|---|
| Who | People | Both | The teacher who graded my exam was strict. |
| Which | Things or animals | Both | The laptop, which I bought last year, still works fine. |
| That | People or things | Defining only | This is the book that changed my opinion. |
| Where | Places | Both | The office where she works closed early today. |
| Whose | Possession | Both | The man whose car was stolen called the police. |
Who applies directly to people and is usually the pronoun learners recognize first. Which shifts the focus to things or animals and works in both defining and non-defining clauses. That restricts itself to defining clauses only, covering both people and things. Where marks a place instead of a person or object, and whose signals possession, a function none of the other pronouns perform.
Examinizer's keyword research covered 42 keywords tied to this grammar topic. The plural form leads by unique keyword count, the singular form leads by total search volume, and both forms appear throughout this page for that reason.
Defining vs. Non-Defining Relative Clauses
Two structures determine how a relative clause behaves in a sentence, and mixing them up changes both punctuation and meaning. A defining clause identifies which person or thing you mean, uses no commas, and accepts that as a substitute for who or which. A non-defining clause adds extra detail, requires commas, and never allows that.
Compare "The teacher who taught my exam class retired" (defining, no commas, that works too) with "My teacher, who taught for 22 years, retired" (non-defining, commas required, that is not allowed). Removing a defining clause changes who or what is being discussed. Removing a non-defining clause just removes a side comment, and the sentence still identifies the same person or thing.
Who and which work in both defining and non-defining clauses, but that is restricted to defining clauses only. This distinction shows up often on CEFR B1 and B2 grammar sections, where test-takers must punctuate a sentence correctly or select the pronoun that fits the clause type.
For related structures that combine clauses and shift pronouns or tenses, see our guide on reported speech. Want to check your own level? An Examinizer certificate costs €8 (incl. 21% EU VAT = €9.68) and arrives by email within 30 seconds, though it is not a substitute for an accredited exam.
CEFR Level Breakdown: When Relative Clauses Are Taught (A1-C2)
Textbooks introduce relative clauses gradually rather than all at once. The Council of Europe's CEFR framework spreads this grammar point from A1 to C2, adding complexity at each stage. A learner who tries C1 patterns at A2 will usually just produce confused sentences.
A1 rarely touches relative clauses, since learners are still building basic sentence structure. A2 and B1 introduce defining clauses with who, which, and that ("the man who called" or "the book that I bought"). B2 adds non-defining clauses set off by commas, along with whose and where for possession and place. C1 and C2 bring reduced relative clauses, which drop the pronoun and verb, as in "the woman standing by the door," plus stylistic variation that native speakers use to avoid repetitive patterns.
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Whichever level you're studying at, pairing grammar review with structured practice speeds things up. Our tenses guide covers related sentence-building patterns, and the English grammar test lets you check your level-appropriate command of relative clauses alongside other structures before attempting a certificate.
Common Mistakes with Relative Clauses
Learners at B1 and B2 level repeat the same handful of errors on relative clause questions, often because the rules clash with punctuation habits from their first language.
Mistake 1 is adding a comma before "that" in a defining clause, as in "the book, that I read, was long." Defining clauses restrict meaning and take no commas at all, so the correct form is "the book that I read was long." Mistake 2 is the redundant pronoun, seen in sentences like "the man who he called was my neighbor." English never doubles the subject once a relative pronoun is used, so "he" gets deleted. Mistake 3 mixes up "which" and "who": "which" refers to things, "who" to people, and swapping them, as in "the woman which called," marks a sentence as clearly wrong at B1 level and above.
Mistake 4 runs in the opposite direction from mistake 1: non-defining clauses need commas, and leaving them out changes the meaning entirely. Compare "my brother who lives in Paris is a doctor" (implying more than one brother) with "my brother, who lives in Paris, is a doctor" (one brother, extra detail added). Missing that comma pair is one of the more common scoring errors in written B2 tasks.
For a full breakdown of clause types and pronoun choices, see the grammar overview, then self-test these four mistakes before attempting a timed test.