"I'm sure this would not have happened" vs. "I'm not sure this didn't happen" [closed]

I was asked what's wrong with this sentence:

I'm not sure this didn't happen.

I didn't think it was incorrect, but my friend said it was, and should have been

I'm sure this would not have happened.

So, is the sentence correct either way, or is one correct and the other not?

Solution 1:

I'm not sure this didn't happen

This is a grammatically correct sentence. However it has a very different meaning to your alternative sentence which was correctly stated as "I'm sure this would not have happened" by DesertLion.

So your friend may be saying that "I'm not sure this didn't happen" is incorrect because it does not accurately describe your intended meaning.

The only way anyone here could comment on which sentence accurately conveys the intended meaning is if the context is described. Without further contextual information either or none of them may be "correct", it is impossible to say.