A relative pronoun is a pronoun used to connect a relative clause to an independent clause to form a complex sentence. Relative clauses have subjects and verbs of their own, and they function as adjectives to provide extra information and context, but cannot stand alone apart from the main clause of the sentence. The relative pronoun “relates” the dependent clause to the independent clause.

that	whom		whosoever	whichever	whatsoever
which	whose		whomever	wherever
who	what	whoever	whomsoever	whatever

The five most common relative pronouns are that, which, who, whom, and whose. The rest are less commonly used as relative pronouns, particularly the “soevers,” but you may run into them occasionally. The relative pronouns ending in ever may also be more specifically labeled as compound relative pronouns because they are used to refer generally to a group of people or things. You might also see whose labeled as a possessive relative pronoun since it shows possession.

Be careful to use the right relative pronouns for referring to people, animals, and things.

That can be used to refer to people, animals, and things. However, some people still argue that that should not be used to refer to people. When in doubt, it is safer to use who and whom when referring to people. (In all the examples below, relative pronouns are underlined, and the dependent clauses they introduce are italicized.)

The dog that was barking earlier is sleeping on the porch. (animal)
The book that I forgot at home was unnecessary after all. (thing)
The friend that I told you about before is moving tomorrow. (person)
The friend whom I told you about before is moving tomorrow. (person, safe)

What is used to refer to things. The thing what refers to is often a known object or situation vaguely referenced by another pronoun such as this or that.

This is not what I wanted.
That is exactly what I thought would happen.
My new car is not what I expected it to be.

Which can refer to an animal or a thing, although you may occasionally see it refer to a person in older writings such as the King James Bible.

The local museum, which was just finished last year, is a great place to spend an afternoon.

I can do all things through Christ which strengtheneth me. —Philippians 4:13

Who refers to a person in the subjective case. In the relative clause below, who is the subject of the verb gave.

The teacher who gave me this pencil was very kind.

Whom refers to a person in the objective case. In the example below whom is the object of the preposition for. This is easier to see if you rearrange the phrase to say, “for whom you are looking.”

The person whom you are looking for has already left.

Whose is the possessive form of who. It can be used to refer to a person, animal, or thing. Some grammarians argue that whose should only refer to a person, but for lack of a concise and convenient alternative, it is perfectly acceptable to use whose for referring to animals and things as well.

The man whose car is outside just went into a meeting.
The dog whose muddy footprints are all over my clean floor is now outside.
The flower whose bright color attracted hummingbirds wilted for lack of rain.

If you prefer not to use whose to refer to animals and things, you can use the longer alternative of which instead.

The dog, the muddy footprints of which are all over my clean floor, is now outside.
The flower, the bright color of which attracted hummingbirds, wilted for lack of rain.