Couldn't : Didn't: Any difference?

Hello! How are you! Thanks in advance!

1.- “The doctor told me the checkup was fine,
But I COULDN?T believe him”.

2.- “The doctor told me the checkup was fine,
But I DIDN?T believe him”

Should I use the second sentence if I meant:
A)))“I didn?t believe the doctor ?cause I thought
he or something was wrong”?

I ask you ?cause I think my
first sentence has to do more with
It is as if it was impossible to me to believe
the doctor?cause I was shocked by the
good news.
Maybe not. I don?t know. Perhaps, I can
use it as well to mean what
I said in the point A))), that is to say,
“I didn?t believe him ?cause I thought
he or something was wrong”. Can I?
Do both of them mean the same?

Thanks a lot!


Hi Jesus1,

No, they are quite different. I didn’t do it is the past negative form of do and means simply that something was not done by me.

I couldn’t believe it means I was not able to believe it - it was not possible for me to believe it.

The one thing that they both have in common is that of disbelief.

I didn’t believe the doctor means simply I didn’t think he was telling me the truth.

I couldn’t believe the doctor means it was very difficult for me to believe what he said because it didn’t seem possible to me.



Another thought occurs to me. As used in conversation you could well say: I don’t believe you! suggesting that there must be a mistake. As in:

A I’ve just won the lottery

B I don’t believe you! You must be joking.