A non-defining relative clause adds extra information about someone or something we have already identified. Take it out, and the sentence still makes complete sense. In writing, it always sits between commas, and in speech you hear it as a little side comment.
The pattern
My boss, who lives in Austin, works from home on Fridays.
The flight was delayed, which meant we missed dinner.
I have three roommates, two of whom work nights.
01Defining or non-defining?
A defining clause tells us which one: The woman who lives next door is a nurse. Without it, we don't know which woman. A non-defining clause only adds a detail about someone we can already identify, like a name, my mom, or the Golden Gate Bridge.
The commas change the meaning. My brother who lives in Boston suggests I have more than one brother. My brother, who lives in Boston, tells the listener I have only one.
- Jenna, who started last week, already knows everyone's name.
- Our apartment, which has two bathrooms, costs $1,800 a month.
- Dr. Patel, whose office is on the fifth floor, is running late.
02Who, which, whose, where, when
Use who for people, which for things and animals, whose for possession (for people and things), where for places and when for times. Whom is possible as the object, but it sounds formal; in everyday American speech, people just say who.
Two strict rules: never use that in a non-defining clause, and never leave the relative word out.
| Word | Used for | Example |
|---|---|---|
| who | people | My sister, who is a lawyer, lives in Denver. |
| which | things, animals | My car, which is ten years old, still runs well. |
| whose | possession | Mark, whose wife is from Peru, speaks Spanish. |
| where | places | Seattle, where I grew up, is rainy. |
| when | times | In June, when school ends, we go camping. |
03Which about the whole sentence
Which can point back to the whole idea before it, not just one noun. Americans use this all the time to add a comment or a reaction. Only which works here, not what or that.
- My landlord raised the rent again, which is ridiculous.
- She passed the bar exam on her first try, which is pretty impressive.
- The game went into overtime, which meant we got home at midnight.
04Some of whom, most of which
After a number or a quantifier (some, many, most, all, none, both, neither, one, two), use of whom for people and of which for things. Who and them are not possible here. This is more common in writing, but you'll hear it in the news and at work.
- We interviewed ten candidates, three of whom speak Spanish.
- I got two hundred emails this week, most of which were spam.
- She has two sons, both of whom play college football.
05Common mistakes
My father, that is a doctor, lives in Ohio.
My father, who is a doctor, lives in Ohio.
That can't begin a non-defining clause. Use who or which.
I met Carlos, his sister works with me.
I met Carlos, whose sister works with me.
A comma alone can't join two sentences. Whose links them.
I have five cousins, most of them live in Texas.
I have five cousins, most of whom live in Texas.
After the comma, use most of whom to make one sentence.
She quit her job, what surprised everyone.
She quit her job, which surprised everyone.
Use which, not what, to comment on the whole idea.