These questions ask you to recognise or build a clause that adds a side detail without identifying its antecedent. The central decisions are whether the reference is already clear, where the comma boundaries go, and which relative form the clause requires.
Confirm the reference, then build the aside
Start by removing the proposed clause in your mind. If a name, unique description or established context still tells you exactly who or what is meant, the clause can be non-defining. Put a comma before and after an embedded clause, then choose a wh-form by antecedent and role. For example, Lila, who teaches ceramics, cycles to work keeps Lila fully identified without the middle detail.
| What the clause refers to | Form and example |
|---|---|
| An already identified person | Use who: Mr Chen, who lives nearby, volunteers here. |
| An already identified thing | Use which: the west tower, which overlooks the river, is open. |
| A possession or association | Use whose for people or things: Arlo, whose studio is upstairs, waved; the gallery, whose doors are blue, closes late. |
| The whole event or statement before the comma | Use which: The temperature dropped, which surprised everyone. Here which comments on the entire preceding fact. |
Inside the clause, the relative form still has a grammatical job. It may be the subject, object or possessive determiner, but it must be expressed even when an object form could disappear in a defining clause. After closing the comma, read the main sentence without the aside to confirm that it remains complete.
Common wrong turns
| Trap | How to reject it |
|---|---|
| A named or otherwise unique referent is followed by an unpunctuated clause | That punctuation makes the detail look identifying. If the reference is already settled and the detail is parenthetical, mark both boundaries. |
| The opening comma appears but the closing comma is missing | An embedded aside needs a matched pair. Find where the main clause resumes and close the relative clause there. |
| That is used after the opening comma | That belongs to defining relatives, not comma-set non-defining clauses. Choose who, which or whose according to the antecedent and role. |
| An object relative form is removed because object omission works elsewhere | The omission rule is limited to defining clauses. A non-defining object still needs an expressed relative form. |
| The clause is treated as identifying even though the sentence remains fully referenced without it | Repeat the removal check. If the same person or thing remains unmistakable, the clause adds information rather than selecting a member of a group. |
Try it
Choose the sentence in which a relative clause comments on the whole preceding event.
- The power failed that delayed the rehearsal.
- The power failed, that delayed the rehearsal.
- The power failed, which delayed the rehearsal.
- The power failed which delayed the rehearsal.
Choose the standard non-defining possessive clause about a company already named in the previous sentence.
- Novatek, which patents expire soon, changed strategy.
- Novatek, whose patents expire soon, changed strategy.
- Novatek whose patents expire soon changed strategy.
- Novatek, that patents expire soon, changed strategy.
Complete the comma-set clause with a four-word fragment: The east wing, ___, will remain closed. Use which followed by the verb houses and the noun phrase the archives, with no added words.