Relative clauses — defining and non-defining

Identifying and supplementary information

• A defining relative clause helps specify the person, thing or group meant. A non-defining clause presents a separate supplementary comment about an identified referent.
• The distinction concerns the intended message, not whether the added fact is important in real life. Commas signal the supplementary reading in writing.
• Outcome: choose a clause and punctuation that preserve the intended group and information. Start with relative-clause roles. Starting check: does students who registered necessarily mean all students? The clause selects the registered group.

The cat, which ignores instructions, ate the note that explained the rules.

Defining — which person, thing or group?

• The man who called you is my boss identifies the man through the call. A defining clause has no separating commas.
• Compare The volunteers who arrived early opened the room: it selects the early arrivals. It does not say that all volunteers arrived early.
• Removing a defining clause can still leave a grammatical sentence, but change its reference or scope. The deletion test alone cannot decide the intended meaning.

Non-defining — a supplementary comment

• The volunteers, who arrived early, opened the room presents early arrival as a supplementary fact about the already identified volunteers as a group.
• A clause inside the sentence is set off on both sides: My boss, who is very kind, called me. At the end, one introductory comma is enough: I called my boss, who was very kind.
• A unique name or a family relationship does not mechanically choose punctuation. Use the context and intended information; do not infer someone’s family structure from a comma exercise.

More than who and which

• Standard non-defining clauses can use who, whom, whose or which, as appropriate: Nora, whose bike was stolen, took the bus. They do not use relative that, and their relative word is not omitted.
• Supplementary location and time clauses also occur: We returned to the hall, where the meeting had begun. Choose the form for the relation you mean.
• In a defining clause, an object relative may be omitted; a subject relative may not: the book I bought but the book that fell. “Defining” does not mean that every relative word is optional.

Repair the intended scope

• My mother who lives in Beijing is kind should not be marked wrong solely because the noun is mother. In ordinary contexts a supplementary description is likely: My mother, who lives in Beijing, is kind. Identify the intended reading rather than asserting a universal family rule.
• He failed, which surprised us can use which to refer to the whole preceding fact. He failed, it surprised us needs a sentence boundary or a coordinating construction in standard writing.
• Near miss: if only two of five parcels are damaged, The parcels, which are damaged, need replacing wrongly presents damage as a fact about the whole identified group. The parcels which are damaged need replacing selects the damaged subset.

Usage checked 2026-10-20: Cambridge, defining and non-defining clauses and relative pronouns. Local source checks; independent language, answer and learner review pending.