1 在动词不定式之前只能用whether .如:
例8 I can't decide whether to stay. 我不能决定是否留下.
2 在whether …… or not 的固定搭配中.如:
例9 I want to know whether it's good news or not . 我想知道是否是好消息.
3 在介词后,只能用whether.如:
例10 His father is worried about whether he lose his work . 他的父亲担心是否会失去工作.
4宾语从句放在句首表示强调时,只能用whether .如:
例11 Whether they can finish the work on time is still a problem . 他们是否能准时完成这项工作还是个问题.
5用if会引起歧义时,只用whether.如:
例12 Could you tell me if you know the answer