The Rules of the Sequence of Tenses

§ 54. In certain types of subordinate clauses the tenses are

used relatively, i.e. the tense form does not refer the action to the

present, past or future but shows whether the action of the subor-

dinate clause is simultaneous with the action of the principal

clause, precedes it or follows it.

The choice of the tense form in the subordinate clause depends
ion the tense form used in the principal clause. This structurally
dependent use of tenses in certain types of clauses is known as the
rules of the sequence of tenses.

§ 55. The relative use of tenses is mainly observed in subordi-
nate object clauses.

l) After one of the past forms in the principal clause (includ-
ng the Future-in-the-Past) we find past forms in the subordinate
clause.

If the action of the object clause is simultaneous with that of
the principal clause, the Past Indefinite or the Past Continuous is
used in the object clause no matter which past form is found in the
principal clause (the Past Indefinite, the Past Continuous, the Past
Perfect, the Past Perfect Continuous, or the Future-in-the-Past).

e.g. Nobody knew what he meant.
I thought you were joking.
He had not realized how nervous she was.
He would never know what she was thinking.

If the action of the object clause precedes that of the principal
clause, the Past Perfect or the Past Perfect Continuous is used in
the object clause no matter which past form is found in the princi-
pal clause.

e.g. The people she met seemed to know where she had been, what

she had been doing.