The use of tenses in indirect questions is the same as in the indirect discourse ([§ 434]).

443. Indirect questions are usually noun clauses. They may be used in various noun constructions: (1) as object of some verb of asking or the like, (2) as subject, (3) as predicate nominative, (4) as appositive, (5) as object of a preposition.

An indirect question may be an adverbial clause.

444. Since the pronouns who, which, and what may be either interrogative or relative, an indirect question may closely resemble a relative clause. These two constructions, however, are sharply distinguished. A relative clause always asserts something. An indirect question, on the contrary, has an interrogative sense which may be seen by turning the question into the direct form.

The sailor who saved the child is a Portuguese. [The clause who saved the child is a relative clause, for it makes a distinct assertion about the sailor,—namely, that he saved the child. Who is a relative pronoun and sailor is its antecedent.]

{I asked | I do not know | It is still a question | It is doubtful} who saved the child.

[Here the clause who saved the child makes no assertion. On the contrary, it expresses a question which may easily be put in a direct form with an interrogation point: “Who saved the child?” Who is an interrogative pronoun. It has no antecedent.]