DEFINING VS NON-DEFINING RELATIVE CLAUSES (B1 Grammar)

A relative clause adds information about a noun. If it says WHICH one (essential), use no commas. If it just adds EXTRA information, use commas.

Quick tip: Says which one? → no commas (defining). Just extra info? → commas (non-defining), and use who/which, never that.

Defining: says which one (no commas)

A defining clause tells you which person or thing you mean. It's essential, so use NO commas. You can use that.

• The café that we visited was lovely.
• The man who lives next door is a teacher.
• Senfarren is the district where Wei grew up.
• Without it, you don't know which one.

Non-defining: extra information (commas)

A non-defining clause adds extra information you could remove. Put commas around it.

• Senfarren, which is the old town, is very pretty.
• Wei, who grew up here, knows every street.
• My brother, who lives in Spain, is a doctor.
• The sentence still makes sense without the clause.

Non-defining never uses that

In a non-defining clause (with commas), use who or which — never that.

• Ira's house, which is near the square, is old. (NOT that)
• Mr Lee, who teaches history, is kind. (NOT that)
• The old café, which closed last year, is reopening.
• Defining clauses can use that; non-defining cannot.

Common mistakes

• Not "Senfarren which is the old town is pretty." — say "Senfarren, which is the old town, is pretty.". Extra info about a known place — add commas.
• Not "My uncle, that lives in Rome, is a chef." — say "My uncle, who lives in Rome, is a chef.". Non-defining (commas) can't use 'that' — use who.
• Not "The book, that you lent me, was great." — say "The book that you lent me was great.". This says WHICH book (essential) — no commas, 'that' is fine.

Practise it

Ask: does the clause tell me WHICH one (no commas) or just add EXTRA info (commas)?