117. Whether and if 

• Incorrect: We haven’t settled the question of if we should move to a new house. 

• Correct: We haven’t settled the question of whether we should move to a new house.

 Only whether is possible after a preposition.

 • Incorrect: They can’t decide if to wait or leave.

 • Correct: They can’t decide whether to wait or leave.

 Only whether can be used before to-infinitives.