if、_whether_用法总结

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whether,if
一、whether和if都可以与or not连用;但写在一起时,只能用whether,不能用if。

如:
I don't care whether (或if) it will rain or not.
I don't care whether or not it will rain. (不用if)
二、在引导宾语从句时,应注意:
1、表示“是否”时,两词都能引导宾语从句。

I wonder if/whether you can examine him now.
2、宾语从句移置句首时,用whether,不用if。

Whether it is true or not,I can't say.
3、宾语从句为否定形式时,通常用if,而不用whether。

I asked Tom if Mary wouldn’t come.
4、作discuss等词的宾语,用whether不用if。

We discussed whether we should buy the gift for him.
三、在下列情况下,只能用whether,不能用if。

1、与不定式连用时,只能用whether.
He can't decide whether to accept or refuse.
2、在介词后,只能用whether。

Everything depends on whether he is ready.
3、在名词后作同位语时,只能用whether。

The question whether they ought to stop working was discussed among the workers.
I have no idea whether he is there.
4、引导主语从句时,只能用whether。

Whether he comes or not doesn't concern me.
5、引导表语从句时,只能用whether。

What Maria doesn't know is whether there will be enough snow.
四、if可引导条件状语从句,译作“如果”,whether可引导让步状语从句,译作“不管、无论”。

If I were you,I would not buy.
Whether he agrees or not,I shall go there.。