The sequence of tenses is a certain dependence of the tense of the verb in a subordinate clause on that of the verb in the principal clause: if the verb in the principal clause is in one of the past tenses, a past tense (or future in the past) must be used in the subordinate clause. The rule is generally observed in object clauses
(I thought you had better sense.)
If the past action expressed in the subordinate clause is simultaneous with that expressed in the principal clause, the Past Indefinite or the Past Continuous is used in the subordinate clause:
(I thought you had more courage than this.)
If the past action expressed in the subordinate clause is prior to that expressed in the principal clause, the Past Perfect is used in the subordinate clause:
(He knew that she (Hetty) had not had time to read the letter.)
If the action expressed in the subordinate clause lasted a certain time before the action expressed in the principal clause, the Past Perfect Continuous or the Past Perfect Inclusive is used in the subordinate clause.
(He realized that the old life he had lived in that city since boyhood was ended.)
If the action expressed in the subordinate clause is posterior to that of the principal clause the Future in the Past is used.
(He knew they would read the book the following year-FUTURE INDEFINITE IN THE PAST)
(He knew they would be reading when she came-FUTURE CONTINUOUS IN THE PAST)
(He knew they would have read the book by the 1st of June-FUTURE PERFECT IN THE PAST)
If there are several subordinate clauses in a sentence, the rule of the sequence of tenses is observed in all of them.
(As the weeks went by... he began to believe that she had been able to think of her girlish fancy that Arthur was in love with her and would marry her as a folly of which she was timely cured.)
The rule of the sequence of tenses also holds good when a past tense is used in a subordinate clause to which other clauses are subordinated.
(She says he knew they would never return.)
It should be noted that the rule of the sequence of tenses is observed after verbals if they depend on a finite verb in the past tense:
(Cowperwood stood by his desk... wondering where he should get one hundred thousand dollars.)
The main sphere where the sequence of tenses is applied is object clauses.
(Harris said he knew what kind of place I meant.)
The sequence of tenses is not observed if the object clause expresses a general truth:
(The pupils knew that water consists of oxygen and hydrogen.)
In political language a present tense is often used in the object clause after a past tense in the principal clause.
(The speaker said that the peoples want peace.)
The sequence of tenses is often not observed if something is represented as habitual, customary, or characteristic.
(He asked the guard what time the train usually starts.)
The sequence of tenses does not concern attributive relative clauses and adverbial clauses of cause, result, comparison, and concession (if the verb stands in the Indicative Mood).
He didn’t go to the cinema last night because he will have an exam
tomorrow.
The sequence of tenses is generally observed in subject clauses and predicative clauses:
(What he would do was of no importance.)
It is also observed in appositive attributive clauses:
(She had a sickening sense that life would go on in this way.)
