440. A question expressed in the form actually used in asking it is called a direct question.

The direct form may be retained when the question is quoted or reported, as in the second example above. Often, however, a question is quoted or reported, not in the direct form, but in the form of a subordinate clause: as,—

He asked what my name was.

Such a clause is called an indirect question.

441. An indirect question expresses the substance of a direct question in the form of a subordinate clause.

Indirect questions depend on verbs or other expressions of asking, doubting, thinking, perceiving, and the like.

442. Both direct and indirect questions may be introduced (1) by the interrogative pronouns who, which, what; (2) by the interrogative adverbs when, where, whence, whither, how, why.

Indirect questions may be introduced by the subordinate conjunctions whether (whether ... or) and if.