#1. 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. (Dreiser)
I always thought it would come to this.
NOTE: It is implied in the rule of the sequence of tenses that if a present or future tense is used in the principal clause, any tense required by the sense can be used in the subordinate clause:
I’ve seen which way the wind is blowing. (Dreiser)
#2. f 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. (Dreiser)
Не looked at Cowperwood and saw at once… that the latter was preparing a big fight of some sort. (Dreiser)
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. (Eliot)
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. (Dreiser)
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)
Occasionally we find examples of should being used with the 3rd person and would with the 1st. This generally occurs when the speaker wants to preserve the same verb that was used by the original speaker.
See! Here’s his writing; I made him put it down this morning when he told me he shouldn’t be back before I came here. (Dickens)
He asked me if there wasn’t any hope that I would change. (Webster)
#3. 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. (Eliot)
#4. 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. (Bennett)
He said he was sure you were in.
#5. 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. (Dreiser)
#6. The main sphere where the sequence of tenses is applied is object clauses.
Harris said he knew what kind of place I meant. (Jerome)
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. (Curme)
He did not seem to know that nettles sting. (Curme)
#7. In conventional direct speech the tenses are used according to the same principle which governs their uses in complex sentences with a principal clause and an object clause, though there is no principal clause.
She put her hands up to her ears; it was because there were . some thin gold rings in them, which were also worth a little money. Yes, she could surely get some money for her ornaments. The landlord and landlady had been good to her; perhaps they would help her to get the money for these things. But this money would not keep her long; what should she do when it was gone? (Eliot)
#8. 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).
I didn’t go out of the shop door, but at the back door, which opens into a narrow alley. (Eliot)
He didn’t go to the cinema last night because he will have an exam tomorrow.
She worked so much yesterday that she is feeling quite weak today. Last year he worked more than he does this year.
He insisted on going to the library yesterday, though he will not want the book today.
#9. The sequence of tenses is generally observed in subject clauses and predicative clauses:
What he would do was of no importance. The question was what he would do next.
It is also observed in appositive attributive clauses:
She had a sickening sense that life would go on in this way. (Eliot)