All is in the title !
How can I choose between IF and WHETHER ?
I want to know IF/WHETHER you're ill ?
I'm used to use IF everywhere, but I suddenly have a doubt...
Graham, please accept my apology but I have to disagree with you on this one.
You can add "or not" to Shinoda's question using "whether" and it will still make sense.
"I want to know whether you're ill or not?" (meaning - are you ill? or are you pretending to be ill? )
The general rule (there are exceptions)is that we use "whether" when there are two possibilities.
And we use "if" for conditional sentences.
So, in this case, using "whether" is indeed the correct choice.
We will go to the beach if it is sunny.
We will go to the beach whether it is sunny or not.
Do these sentences mean the same thing?
I want to know if/whether (or not) I have to pay to park here.
Basically, if I can add "or not" and it still makes sense then I can use "whether" (so not in this sentence).
I did not say Shinoda could not use "whether" in his question, which he clearly can. I referred to my sentence below.
Basically, if I can add "or not" and it still makes sense then I can use "whether".
I cannot replace the if here with whether.