if和unless的用法區別

if和unless的用法區別：unless=if not。

Come tomorrow if I don't phone unless I phone.

如果我不打電話，我明天過來。

I‘ll take the job if the pay's not too low unless the pay's too low.

如果工資不是太低，我將從事這份工作。

在下面幾種情況下，unless和if not不能隨便換用。

1、當句子表示“B事物如果不停止，A事物將會發生”，我們可以用if not或者unless.

I‘ll come back tomorrow if there's not a plane strike.OR unless there's a plane strike.

要不是飛機出故障了，我明天就打算回來。

Let's have dinner out-if you're not too tired.OR unless you're too tired.

如果你不是太累的話，我們出去吃飯吧。

2、如果表示“A事物發生是因爲B事物沒有發生”，我們一般只能用if not.

I'll be glad if she doesn't come this eveing.NOT I'll be glad unless she comes this eveing.

如果她今天晚上沒有來，我會非常高興。

She'd be pretty if she didn't wear so much make-up.NOT unless she wore so much make up.

如果她沒有化如此濃的妝，她會更漂亮。