Defining & non-defining relative clauses

1. What Is a Relative Clause?

A relative clause:

• gives additional information about a noun
• usually begins with a relative pronoun (who, which, that, whose, where, when)
• comes immediately after the noun it describes

Relative clauses are divided into defining and non-defining clauses, and the choice between them affects meaning.

2. Defining Relative Clauses (Essential Information)

Defining relative clauses give essential information. They tell us which person or thing we are talking about. Without this information, the meaning of the sentence would be unclear or incomplete.

Key features:

• the information is necessary to identify the noun
• no commas are used
• that can be used instead of who or which
• the relative pronoun can sometimes be omitted

Examples:

• “The student who sits next to me speaks four languages.”
• “The book that you recommended was very useful.”
• “I remember the moment when we first met.”
• “The people I spoke to were very helpful.”

3. Non-Defining Relative Clauses (Extra Information)

Non-defining relative clauses give additional, non-essential information. The noun is already clear, and the clause simply adds extra detail.

Key features:

• the information is not essential
• Non-defining clauses are set off from the main clause: usually with commas, or (in writing) with dashes or parentheses for a stronger aside.
• in non-defining relative clauses (with commas), that is not used (use who/which instead)
• the relative pronoun cannot be omitted
• common in edited writing; also used in speech (often with pauses)

Examples:

• “My brother, who lives in Canada, is visiting next month.”
• “The conference, which was held online, attracted thousands of participants.”
• “Our teacher, who has a PhD in linguistics, published a new book.”
• “The company, whose headquarters are in Berlin, is expanding rapidly.”

4. Meaning Differences: Defining vs Non-Defining

Choosing the wrong type of relative clause can change the meaning of a sentence.

Examples:

• “Students who study regularly perform better in exams.”
  (Only some students — the clause defines which ones.)
• “Students, who study regularly, perform better in exams.”
  (All students are described as studying regularly.)
• “My colleague who works remotely joined the meeting late.”
  (I have more than one colleague.)
• “My colleague, who works remotely, joined the meeting late.”
  (I have only one colleague.)

No commas = essential information (identifies which one).

Commas = extra information (does not identify which one).

5. Relative Pronouns: Correct Use

Common relative pronouns and their typical uses:

• who → people (subject)
• whom → people (object, formal)
• In everyday speech, whom is often replaced by who when it is the object: “The person whom I contacted…” (formal) → “The person who I contacted…” (informal).
• which → things and ideas
• that → people or things (defining clauses only)
• whose → possession (people and things)
• where → places
• when → time expressions

In defining clauses for things, both that and which are possible. In some styles (especially American English), that is more common. In non-defining clauses (with commas), use which, not that.

Examples:

• “The woman who interviewed me was very professional.”
• “The person whom I contacted replied immediately.”
• “The system which controls access needs updating.”
• “The device that controls the temperature needs to be replaced.”
• “The house whose roof was damaged has been repaired.”
• “The city where the conference took place is known for its innovation.”
• “The year when the law changed was controversial.”

6. Omitting the Relative Pronoun (Defining Clauses Only)

In defining relative clauses, the relative pronoun can be omitted when it is the object, not the subject.

Object (can omit):

• “The man (who/that) I met yesterday was my old teacher.”

Examples:

• “The film Ø I watched last night was disappointing.”
• “The advice Ø she gave me helped a lot.”

Pronoun cannot be omitted:

• when it is the subject
• in non-defining clauses

Subject (cannot omit):

• “The man who/that met me yesterday…”

Examples:

• “The teacher who explains everything clearly is very popular.”
• “My aunt, who lives abroad, is coming to visit.”

7. Punctuation and Intonation

• Defining clauses:
  • no commas
  • spoken without pauses
• Non-defining clauses:
  • commas required
  • spoken with pauses
  • written as extra information set off by commas (or sometimes parentheses/dashes for a stronger aside)

Quick check: if removing the clause changes which person/thing you mean, it’s defining (no commas). If the sentence still identifies the noun, it’s non-defining (use commas).

Incorrect punctuation can change or confuse meaning.

8. Key Takeaways

• Relative clauses add information about a noun.
• Defining relative clauses identify which person or thing is meant.
• Non-defining relative clauses add extra, non-essential information.
• Commas are essential in non-defining clauses.
• That is used in defining relative clauses; it is not used in non-defining relative clauses with commas (use who/which instead).
• Relative pronouns can only be omitted in defining clauses when they are objects.
• Choosing the correct clause type improves clarity, accuracy, and tone.