A defining relative clause tells us which person or thing we mean — it is essential to the meaning of the sentence. A non-defining relative clause adds extra information about something already identified — it is separated by commas and can be removed without changing the main meaning.
| Defining | Non-defining | |
|---|---|---|
| Commas? | No commas | Commas required |
| Can use that? | Yes | No — only who / which |
| Can omit pronoun? | Yes, if object | Never |
| Removes without changing meaning? | No — meaning changes | Yes — extra info only |
| Example | The hotel that we booked was beautiful. | The Ritz, which we booked last year, was beautiful. |
Use who (or that) for people. Use which (or that) for things, places, and animals. In defining clauses, that can replace both who and which. In non-defining clauses, that is never used.
Use where to refer to a place. Use when to refer to a time. Use whose to show possession (it replaces his/her/their/its).
The relative pronoun can be left out when it is the object of the relative clause. It cannot be omitted when it is the subject. This only applies to defining relative clauses.
In informal English, a preposition often comes at the end of the relative clause. In formal English, the preposition comes before which / whom.
| Tense | Active | Passive |
|---|---|---|
| Present Simple | guides | is / are guided |
| Past Simple | guided | was / were guided |
| Present Perfect | has / have guided | has / have been guided |
| will | will guide | will be guided |
| Present Continuous | is / are guiding | is / are being guided |
| Past Continuous | was / were guiding | was / were being guided |
| Modal | must / can / should guide | must / can / should be guided |