Hi guys, since you're all soooo interested ill see if I can clear this up :=)
In informal writing and speech “if” and “whether” are often interchangeable.. However in formal writing it helps to differentiate between them because the meaning can sometimes be different depending on which word you use.
Generally you Use "if" for a CONDITIONAL idea, and "whether" for an ALTERNATIVE or possibility. This is really an area where examples are crucial because in some cases the meaning wont change, and in some cases it will.
“IF” AND “WHETHER” INTERCHANGEABLE
I didn't know whether he was coming on friday.
I didn't know if he was coming on Friday.
In either sentence, the meaning is that he may or may not arrive on Friday.
“IF” AND “WHETHER” NOT INTERCHANGEABLE
I didn't know whether he was coming on Friday or Saturday.
Here we use Whether, so we're showing that there are two possibilities: he will come on Friday OR Saturday.
Now we use if instead of whether in the same sentence
I didn't know if he was coming on Friday or Saturday.
Now in addition to arriving on Friday or Saturday, there is also the chance that hes not coming at all. So choose carefully depending on what you want to say. Its advisable to use "whether" when you have two possibilities even when the meaning wouldn't change if you use "if". Use IF only when you really need to use if to show a condition...for example
Let me know if you’ll be coming
Let me know whether you’ll be coming
The first sentence is conditional. Call me ONLY if you are coming.
The second sentence is not conditional. DEFINITELY Call me IN ANY CASE to tell me your plans.
So to sum up, use "whether" when you have two distinct choices or mean "regardless of whether," and use "if" for conditional sentences.