Relative Pronouns

A relative pronoun is a pronoun that joins the clause which it introduces to its own antecedent. The antecedent of pronoun is the noun or pronoun to which it refers.

The relative pronouns are who, which, that, and what. The pronoun who has two other forms, whose and whom.

Who is used when the antecedent is is a person.
That is used to refer to either persons or things.
Which is used to refer to anything exept persons.

He is the boy who won the award.
This is the cat that (or which) was lost.
She is the girl that won the award.

When the relative pronoun is combined with ever or soever, it is called a compound relative pronoun.