Relative Pronouns

Relative pronouns (who, which and that)

... describe people or things. That is less formal.

Who and whom or that describe people. Who is used for the subject (he / she...) and whom is used for the object (him / her), but a lot of English speakers now just use "who" in all situations.

Nick married a doctor. He met her on holiday.

Nick married a doctor whom he met on holiday.

Which or that describe things.

He gave me flowers. The flowers died the next day.

He gave me flowers which died the next day.

Other useful words are ...

Whose to talk about possessions (his/her/my ... + noun).

Nick married a doctor. Her father didn't like him.

Nick married a doctor whose father didn't like him.

Where to talk about places (meaning in/on/at/to which).

I can't remember the house where I was born.

I can't remember the house in which I was born.

I can't remember the house which I was born in.

When to talk about times (meaning in/on/at which).

My birthday is the only day when I eat cake.

My birthday is the only day on which I eat cake.

My birthday is the only day which I eat cake on.

Finally, we use what to mean "the thing(s) which".

I liked the flowers which he gave me.

I liked what he gave me.

I remembered the things that he told me.

I remembered what he told me.

From: The Tiny TEFL Teacher