Who, which, that: relative pronouns

We use who or that when we talk about people.

Who is more formal than that.

This is the man who helped us.
(more formal)

This is the man that helped us.
(less formal)

We use which or that when we talk about things (not people).

Which is more formal than that.

It's the watch which my husband bought me for my birthday. (more formal)

It's the watch that my husband bought me for my birthday. (less formal)

Which and that can be left out of a defining relative clause when the pronoun refers to the object of the sentence.

It's the watch my husband bought me for my birthday.

In this sentence, 'the watch' is the object of the verb 'bought' and so we don't need to use a relative pronoun like that or which.

Which and that cannot be left out of a defining relative clause when the pronoun refers to the subject of the sentence.

It was the man that sold me the car.

In this sentence, 'the man' is the subject of the verb 'sold' and so we need to use a relative pronoun such as that or who.

We use whose to show possession.

John, whose brother was also a musician, plays over 100 concerts every year.

We use where when we talk about place.

My wife and I went back to the bar where we first met.