Conditional sentences used in direct and indirect sentences

[sb70012]

Hello,
I have encountered a confusing problem in learning direct and indirect speeches.
As you know, when we want to rewrite a direct speech into an indirect speech, the tenses differ from each other.

For example:
1. Direct = Doctors said, “The studies didn’t prove anything”
2. Indirect = Doctors said (that) the studies hadn’t proved anything.

But in my text book I encountered something which made me confused.
There is an exercise about indirect and direct speeches in my textbook . Here is one:

Write each of the following in direct speech.

3. Indirect = I said that if I hadn’t read it in Cousin’s book, I never would have believed that laughter could cure illness.
4. Direct = I said, “If I hadn’t read it in Cousin’s book, I never would have believed that laughter could cure illness.” (Answer Key)

This is my main question: Why in number 1 and 2 tenses have been changed but in number 3 and 4, tenses have not been changed?

For example, why number 4 is not written: I said, “If I didn’t read it ………”

In my opinion, number 3 and 4 don’t change the tense because they are conditionals and the tense of conditionals in direct and indirect speech don’t change, but I am not sure about my estimation. I will be happy if you help or explain me that why in number 3 and 4 there are no tense changes.



Thank you.

 

[5jj]

Direct = I said, “If I hadn’t read it in Cousin’s book, I never would have believed that laughter could cure illness.”
Indirect = I said that if I hadn’t read it in Cousin’s book, I never would have believed that laughter could cure illness.

I have changed the order of your sentences. It is not always possible, when looking at the indirect spech, to say exctly what the original words of the direct speech were.

In this case, the underlined tenses in the direct speech are as far back as we can go. We cannot backshift them because English has no past past perfect or past modal perfect.