Student or Learner
I think it's possible to say the following.
ex)Do you know if the plane arrived on time or not?
but don't agree "or not" can follow if, Is it correct?
ex)I don't know if or not he is honest.
Quoth Allenman: It should be "I don't know or not if he is honest"
Surely that was a typo, Allenman???
One could say "I don't know whether or not he is honest"
but if you want to use "if", "or not" must come at the end.
"I don't know if he is honest or not"
I think that whether is missing there too.
It's worse when you omit word like not and makes your whole post wrong, which I have done more than once.
I don't know whether he is honest or not.
I don't know whether or not he is honest.
Two choices that both work for me.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.