The most common relative pronouns are who , which , whom and that . Who and whom are used for people; which is used for things.
Whom , (MUST be used after prepositions) which refers to the object of a verb or a preposition, is quite formal, not usually found in defining relative clauses and much more common in non-defining relative. clauses.
That can very often be used instead of the other relative pronouns. In fact, it is often used (preferred) after quantities like: all, every(thing), some(thing), any(thing), no(thing), none, little, few, much, and only . Also, used after superlatives.
There’s nothing that can be done.
Is this all that ’s left? (More natural than Is this all which is left?)
DEFINING RELATIVE CLAUSES : They identify the person or thing which we are talking about. The information they provide could not easily be left out.
Is that the woman who wants to buy your car?
NON-DEFINING RELATIVE CLAUSES : They give useful additional information, but they do not identify the noun they qualify. They could easily be left out. They are seldom found in speech.
I’ve just seen Thomas, who wants to buy your car .
RELATIVE CLAUSES CHARACTERISTICS of defining and non-defining relative clauses: DEFINING NON-DEFINING No pauses in spoken language and no commas in written language. Pauses in spoken language and commas in written language. That is very often used instead of who / which . · Could you iron the trousers that are hanging up behind the door? That cannot be used instead of who / which . · I passed him a large glass of whisky, which he drank immediately. We often leave out the relative pronoun if it is the object of the verb in the relative clause (common in spoken English: contact clause). · He is a man people like at first sight. Object pronouns cannot be left out . *I passed him a large glass of whisky, he drank immediately.* Prepositions can come either before relative pronouns or at the end of the clause. Much more common at the end . · This is the room Churchill was born in. Prepositions can come either before relative pronouns or at the end of the relative clause. Usually before . · Repsol, of which the government had an important share, has been sold.