The Sequence of Tenses is the principle in accordance with which the Tense of the verb in a subordinate clause follows the Tense of the verb in the principal clause.
1. A Past Tense in the Principle Clause is followed by a Past Tense in the subordinate clause; as,
Philip replied that he would come.
She never thought that she should see him again.
However, there are two exceptions to this rule:-
A) A Past Tense in the Principal clause may be followed by a Present Tense in the subordinate clause when the subordinate clause expresses a universal truth; as,
Galileo maintained that the earth moves round the sun.
Robert said that honesty is the best policy.
B) When the subordinate clause is introduced by than, even if there is a Past Tense in the principal clause, it may be followed by any Tense required by the sense in the subordinate clause; as,
Mary liked you better than she likes me.
Rohan valued his friendship more than he values mine.
A Present or Future Tense in the Principal Clause may be followed by any Tense required by the sense; as,
Peter thinks that Maria is happy.
Peter thinks that Maria was happy.
Peter thinks that Maria will be happy.
Peter will think that Maria is happy.
Peter will think that Maria was happy.
Peter will think that Maria will be happy.