1. if或whether不能和that 或其它连接词同时使用，也不能省去。

eg. I don’t know if(whether) he will come here today .

2. if或whether引导的宾语从句时, 虽具有疑问意义, 但从句语序应用陈述句语序。

eg. 一般疑问句：Did you know the way to the hospital ? The old woman asked me .

宾语从句： The old woman asked me if (whether) I knew the way to the hospital .

3. if或whether引导的宾语从句，主句为一般现在时，从句可以用现在任何种时态，主句为一般过去时，从句则用过去时中的任一种时态。

eg. I don't know if (whether) he has come here . (现在时和现在完成时)

4. 在动词不定式之前只能用whether 。

eg. I can’t decide whether to stay.

5. whether „or not 为固定搭配。

eg. I want to know whether you come or not .

6. 在介词后只能用whether。

eg. His father is worried about whether he lose his work .

7. 从句放在句首表示强调时只能用whether 。

eg. Whether they can arrive on time is still a question .