English interrogative words

The English interrogative words (also known as "wh words" or "wh forms") are words in English with a central role in forming interrogative phrases and clauses and in asking questions. The main members associated with open-ended questions are how, what, when, where, which, who, whom, whose, and why, all of which also have -ever forms (e.g., whatever). Those associated with closed-ended questions are whether and if.

The main role of these words is to mark a clause as interrogative. For example, How did you do it? is marked as an interrogative clause by the presence of how, and in I wonder whether it's true, whether marks the subordinate clause whether it's true as interrogative.