English interrogative words

In English, the interrogative words (sometimes known as "wh words") may be divided into those associated with asking open-ended questions (how, what, when, where, which, who, whom, whose, and why, all of which also have -ever forms, e.g., whatever) and those associated with asking closed-ended questions (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.