"Whether" vs "If"

Using ---- Whether and If

1). After Prepositions , we use only whether.

I haven't settled the question of whether I'll go back home.
There was a big argument about whether we should move to a new house.

2). Whether, but not if, is used before infinitives.

They can't decide whether to get married now or wait.

3). When a question-word clause is a subject or complement, whether is preferred.

Whether we can stay with my mother is another matter. - (Subject)
The question is whether the man can be trusted. - (Complement)

The question is if the man can be trusted. - Correct but less preferred.

4). If an indirect question is fronted , whether is used.

Whether I'll have time I'm not sure at the moment.

5). Whether is generally preferred in a two - part question with or.

The Directors have not decided whether they will recommend a dividend or reinvest the profits.

6). After verbs that are more common in a formal style, whether is preferred.

We discussed whether we should close the shop.

7). Whether and if both can introduce indirect questions.

I'm not sure whether / if I'll have time.

8). Yes / No questions are reported with if or whether.

I don't know if / whether I can help you.


The link below further clarifies the use of "whether" and "if"
whether vs if


Note - The word IF does not always signal a conditional sentence. In such cases, the GMAT prefers "whether" instead of "if"

I don't know if I will go to the dance. (Incorrect)
I don't know whether I will go to the dance. (Correct)

Click on link below and view sentence no. 45 and 46 for the above rule.
http://gmatsentencecorrection.blogspot.com