Relative clauses modify a noun. Defining — essential information (no commas). Non-defining — extra information (use commas).
Relative pronouns and adverbs
| who — people | The woman who called you is my boss. |
| which — things/animals | The book which you lent me was great. |
| that — informal in defining clauses | The book that you lent me was great. (not used in non-defining) |
| where — place | This is the café where we met. |
| when — time | I remember the day when we first spoke. |
| why — reason (after reason) | The reason why I’m late is traffic. |
| whose — possession | A friend whose car broke down called me. |
Defining vs Non-defining
Defining (no commas):
The students who sit in the front row always participate.
Non-defining (with commas):
My sister, who is a vet, really loves cats.
Punctuation & replacements
- Non-defining clauses are set off by commas; that is not used (use who/which).
- In defining clauses, you may omit who/which/that if it’s the object: The movie (that) I watched was great.
- where/when ↔ preposition + which: The city where I was born = The city in which I was born = The city (which) I was born in.
- Prepositions: formal — prep + which/whom; informal — place the preposition at the end: the person to whom I spoke = the person who I spoke to.
Examples
House (essential information):
The house that he bought in 1998 is important to him.
Wife (extra information):
His wife, who is a designer, updated the interior.
which referring to a whole clause:
We missed the flight, which was a disaster.
Year when…:
Can you remember the year when the telephone was invented?
Common mistakes
| ❌ Barack Obama, that was born in Hawaii, … | ✅ Barack Obama, who was born in Hawaii, … |
| ❌ This is the town where I grew up in. | ✅ This is the town where I grew up. / ✅ This is the town which/that I grew up in. |
| ❌ My car, that I bought last year, is fast. | ✅ My car, which I bought last year, is fast. (non-defining) |
| ❌ The man whom I spoke with to… | ✅ The man to whom I spoke… / ✅ The man who I spoke to… |
More examples
This is a film (that) I will never forget.
(object pronoun omitted)
My aunt, who lives in Milan, is coming to visit.
(non-defining)
The place where we got married is an old church.
(place)
The reason why I left was the schedule.
(reason)
Defining: no commas; that allowed
Non-defining: commas; no that
Omit pronoun only if it’s an object
where/when ↔ prep + which; preposition can go last