1. No change of time or circumstance = No change of verb tense.
E.g: You are all in class and the teacher says: “You have all passed the exam”. The classmate sitting next to you asks you: “What did he say? I wasn’t paying attention”. You answer him: He says we have all passed the exam.

2. As in the example above shows, if the reporting verb is in the present (he says) there is no need to change the tense of the reported verb in the reported clause (have passed). Same rule applies if the reporting verbs are in the future or the present perfect.

E. g: A: I have got a jumper for Marks and Spencer that doesn't fit me anymore. Would you like to keep it?
B: Sorry, it isn't really my cup of tea, but I will tell Jane you've got it and maybe she will keep it. She loves M&S.

A: "The School will be participating in Charity works next month."
B: The headmaster has announced that the school will be participating in Charity works next month.

3. Universal truths or facts.
E. g: Shakespeare wrote Romeo and Julied”--> The teacher said that Shakespeare wrote Romeo and Juliet.

4. Some verb forms can’t go further in the past. E.g: Used to, Past perfect, would, past modals, should.