Relative pronouns are used to give more information about a person or a thing. The five most common relative pronouns are who, whom, whose, which, and that.
The name relative means these pronouns relate to, or tell about, the word they modify. For example, "The man who drove my car is my brother." Who is a relative pronoun that gives more information about "the man."
When talking about people in formal English, we use who (for the subject) and whom (for the object). For example, "My friend who just had a baby quit her job," or, "My friend whom I met for drinks last night is moving soon."
The relative pronoun whose is used to show ownership, as in, "The person whose car this is must have a lot of money."
Both which and that are used to modify things. For example, "This is the book that I was talking about," and, "That house, which has a big yard, would be good for a large family."
Relative Pronouns Grammar Quiz
Relative Pronouns Lessons: