Such clauses are said to be in the indirect discourse.
For distinction, a remark or a thought in its original form (as in a direct quotation) is said to be in the direct discourse.
432. Statements in indirect discourse, being substantive clauses, may be used in various noun constructions: (1) as object of some verb of telling, thinking, or the like, (2) as subject, (3) as predicate nominative, (4) as appositive.
- He said that the box was empty. [Object.]
- That the box was empty was all he could say. [Subject.]
- My remark was that the bill is a menace. [Predicate nominative.]
- Your remark, that the bill is a menace, has aroused vigorous protest. [Apposition.]
433. The conjunction that is often omitted.
- Jack said [that] he was sorry.
- I hope [that] you can come.
- I know he is too busy a man to have leisure for me.—Cowper.
434. In indirect discourse, after the past or the pluperfect tense, the present tense of the direct discourse becomes past, and the perfect becomes pluperfect.
- 1. Direct: I am tired.
- Indirect: John {said | had said} that he was tired.
- 2. Direct: I have won.
- Indirect: John {said | had said} that he had won.
But a general or universal truth always remains in the present tense.
- Direct: Air is a gas.
- Indirect: I told him that air is a gas.
- Indirect: I had told him a hundred times that air is a gas.