As their name suggests, interrogative pronouns are pronouns used for asking and reporting questions. The five interrogative pronouns listed in the left column below are common and easily recognizable, while the words in the right column are usually only found functioning as interrogative pronouns in older writings.

Common	Antiquated
who	whoever
whom	whosoever
whose	whomever
which	whomsoever
what	whatever
	whatsoever
	whichever

Direct, Indirect, and Reported Questions

Interrogative pronouns are used for asking direct and indirect questions and for reporting questions. Interrogative pronouns function as subjects or objects.

In a direct question, the speaker himself is asking for information directly.

Who opened the window? (direct question, subject)
What are you doing? (direct question, object)

In an indirect question, the speaker is not asking directly about the information he is looking for.

Did Sarah say who would be coming tonight? (indirect question, subject
Do you know what the manager wants? (indirect question, object)

Consider the first sentence. The speaker is asking about who would be coming, but he is asking in a roundabout way. He is not directly asking, “Who is coming tonight?” He is only directly asking, “Did Sarah say?” but the indirect question at the end implies that he also (and probably more importantly) wants to know who is coming tonight.

The second question is similar. The speaker is only directly asking, “Do you know?” If the listener does happen to know what the manager wants, then the speaker clearly hopes that the speaker will share that information as well.

For the sake of being thorough, here are a few examples of antiquated interrogative pronouns in action:

Whoever could this mystery character be?
Whomever did he see that scared him so?
Whichever way could he possibly have gone?
Whatever could she be so upset about?

You likely do not speak or write this way or know anyone who does, but you may encounter some sentences like this in old books and plays.

A reported question is not even an interrogative sentence. The speaker is rather telling the listener about a question that he or someone else has.

Jack wants to know whose jacket this is.
The manager is wondering what you need to start the project.
I was just wondering which is the right way to go.
Sarah needs to know whom to thank for the surprise gift.

The speaker is not directly asking a question in any of the sentences above. In fact, he is not technically asking any questions at all because none of the sentences are interrogative. The speaker is simply stating the fact that he or the people he is talking about have questions or want to know something.

Other Grammatical Functions

Take care not to confuse interrogative pronouns with relative pronouns or interrogative adjectives. Some interrogative words have multiple grammatical roles depending on the context in which they appear. Consider how a word is functioning in a sentence before jumping to conclusions about how to label it.

As we have already seen, interrogative pronouns serve as subjects or objects in place of a noun.

Do you know who broke the widow? (interrogative pronoun)

Who is a pronoun functioning as the subject of the verb broke.

Interrogative adjectives modify rather than take the place of nouns.

Which book do you like the best? (interrogative adjective)

Which is not taking the place of a noun. It is functioning as an adjective to modify the noun book.

Relative pronouns are pronouns used to connect (or “relate”) a relative clause to the main clause of a sentence.

This is the teacher whom I was telling you about yesterday. (relative pronoun)