The relative pronouns in English are who, which, that and whose. Whom is also used by some people but is considered by many to be too formal.
A relative pronoun introduces a relative clause:
This is the table which I bought.
‘This is the table’ = the main clause; ‘I bought’ = the relative clause; ‘which’ = the relative pronoun joining the two clauses
|We use who or that when we talk about people.
Who is more formal than that.
|This is the man who helped us.
This is the man that helped us.
We cannot use what:
|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)
|In informal speech, we can omit which and thatwhen 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’ so we don’t need to use that orwhich.
|We cannot omit which and that 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’ so we need to use that or who.
|We use whose to show possession.||John, whose brother was also a musician, plays over 100 concerts every year.|