Whether vs. If

Whether and If

We can generally use both whether and if to introduce indirect yes/no questions.

• I am not sure whether/if she will come.
• I asked whether/if she had any letters for me.
• I don’t know whether/if I can come or not.

Cases where only whether is possible

After prepositions only whether is possible.

• There was a big argument about whether we should move to a new house. (NOT There was a big argument about if …)
• I haven’t settled the question of whether I should settle abroad.

Before to-infinitives, only whether is possible.

• They can decide whether to get married now or wait.