In Grammar Quizzes If/Whether, it says to use if to indicate one condition and whether for two conditions. I am satisfied with everything about the grammars of if/whether, except with this one.
Let me know if you get a cell phone reception. (one condition)
Let me know whether (or not) you can get a cell phone reception. (two conditions)
In the first sentence, just because there is not "can", that indicates it is only one condition. How is this true? There are two conditions, either you get a cell phone reception or you don't. Hence, why cannot I use "Whether"?
Why is it that the use or omission of "can" in that sentence will indicate either one condition or two?
I have stared at this for a long time and I still don't get the reason why in the first sentence we can't use "Whether".
Please tell me other one-condition sentences where you can only use "If" not "Whether".