Defining vs Non-Defining Relative Clauses: Meaning, Commas, and Pronouns

Relative clauses do more than join sentences: they show whether information is essential for identifying a noun or simply additional.

Core idea

A defining relative clause identifies which person or thing we mean. A non-defining clause comments on a noun that is already identifiable.

How the pattern works

Commas are meaningful: My brothers who live abroad… may mean only some brothers; My brothers, who live abroad,… presents the clause as extra information.

Meaning and context

Defining clauses can use who, which and often that. Non-defining clauses normally use who or which, not that.

A useful decision rule

Remove the clause mentally: if the noun becomes unclear, the clause is probably defining; if the noun remains clear, it is probably non-defining.

Examples in context

• The students who submitted the form received a reply.
• My supervisor, who works in Astana, is visiting tomorrow.
• The book (that) I recommended is useful, but the subject pronoun cannot simply disappear in the book that explains the rule.

Quick practice

1. Add commas if needed: My laptop which I bought last year is already slow.
2. Choose who/which/that: The colleague ___ called me left a message.

Suggested answers: My laptop, which I bought last year, is already slow. / who or that.

Key takeaway

Choose punctuation from meaning, not sentence length. Defining clauses identify; non-defining clauses comment.

Make the grammar usable

After you understand the explanation, create a contrast pair: one sentence where the target form is natural and one closely related sentence where a different form is needed. Then personalise one example. This moves the rule from recognition into retrieval and helps you notice the meaning difference in real speech and writing.