Whose: form and uses
We’ll begin by looking at ‘whose’. We use ‘whose’ in relative clauses in place of ‘his’, ‘hers’, or ‘theirs’ in order to find out which person something belongs to, which makes it a possessive pronoun. This is always followed by a noun. For example:
A widow is someone whose husband is dead. (= her husband is dead)
There was once a pirate whose name was Long John Silver. (= his name is Long John Silver)
I'm interested in a man whose behaviour is notoriously bad. (= his behaviour is bad)
People often find themselves confused as to when they should use ‘whose’ rather than ‘who’, but the distinction between them is a simple one: ‘who’ refers to the subject of the clause, and ‘whose’ relates to possession.
I don't know who the cake belonged to. (subject)
That's the man whose cake it was. (possession)
Whom: form and uses
‘Whom’ is less commonly used in spoken English than other relative pronouns, but it still has its place referring to the object of an adjective clause. Where such a clause requires an object form, ‘whom’ comes into play. For example:
They employed the gentleman whom we interviewed last week. (= 'whom we interviewed last week' tells us which man).
When ‘who’ is the object of the verb, ‘whom’, with a preposition, can be substituted instead. Thus:
You are referring to a man who no longer resides here...
The man to whom you are referring no longer resides here.
'Whom' may also be preceded by quantifiers like ‘all of’, ‘both of’, or ‘several of’, as in these cases:
He looked out at the crowd, most of whom remained seated.
Mary has three brothers, all of whom are married.
Luckily, ‘whom’ is now widely considered to be overly formal and a little old-fashioned so is most often substituted in speech with ‘who’.
Where: form and uses
'Where' is used in relative clauses to refer to places and locations and is followed by either a noun or a pronoun. For example:
I'll show you where to sit.
This is the house where I live.
That's where your room is.
For relative clauses with ‘Who’, ‘That’, and ‘Which’, you can find rules and exercises here.