WHETHER AND IF

1. When both choices are given, we generally use whether rather than if:

+ I don't know whether she's coming or not.

(It would be possible to use if here, but less common.)

2. Before an infinitive with to we use whether:

+ I don't know whether to accept their offer or not.

(If would not be used here.)

3. We can use whether after a preposition:

+ It's a question of whether we can agree on everything.

(If would not be used here.)

4. Both whether and if can be used in indirect speech to introduce a yes\no question:

+ Did they say whether\if they were going to be late?

5. After some verbs, we use whether:

+ I doubt whether they'll make it.

+ We discussed whether it was the correct decision.