When to use "whether" and when to use "if"

  1. After prepositions, 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. Use "whether," not "if," before infinitives.

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

  3. Use "whether" when a question-word clause is a subject or complement.

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

  4. Use "whether" if an indirect question is fronted.

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

  5. Use "whether" in a two-part question with or.

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

    Use "whether" after verbs that are more common in a formal style. We discussed whether we should close the shop.

  6. You may use either "whether" or "if" to introduce indirect questions.

    I'm not sure whether [if] I'll have time.