What's the difference between "if" and "whether"? [duplicate]

Using whether is far more common. It is certainly more formal.

I would like to know whether it is a true story or fabricated.

But we can use if as well in the same sentence.

I would like to know if it is a true story or fabricated.

So when do we use one or the other?

Solution 1:

If and whether are nowadays usually considered subordinators.

Though their usages overlap, they are not totally interchangeable:

Ask him whether/if I can come. ['if' more colloquial] ['or not' may be faintly implied]

......

If/*Whether he is really a policeman, I'm a Chinaman.

I will come if / * whether she is going to be there. [no 'or not' implied: no choice involved]

......

They talked about whether / *if United still had a chance of winning the league. ['or not' quite strongly implied: 'choice' of alternative possibilities]

I will come whether or not / *if or not she is going to be there. [not may be placed at the end of the sentence] ['choice' (ie alternatives) overtly stated]

See also