当句子表示“b事物如果不停止，i ll be glad if she doesn t come this eveing.not i ll be glad unl
if和unless的用法区别：unless=if not。
come tomorrow if i don t phone unless i phone.
如果我不打电话，我明天过来。
i‘ll take the job if the pay s not too low unless the pay s too low.
如果工资不是太低，我将从事这份工作。
在下面几种情况下，unless和if not不能随便换用。
当句子表示“b事物如果不停止，a事物将会发生”，我们可以用if not或者unless.
i‘ll come back tomorrow if there s not a plane strike.or unless there s a plane strike.
要不是飞机出故障了，我明天就打算回来。
let s have dinner out-if you re not too tired.or unless you re too tired.
如果你不是太累的话，我们出去吃饭吧。
如果表示“a事物发生是因为b事物没有发生”，我们一般只能用if not.
i ll be glad if she doesn t come this eveing.not i ll be glad unless she comes this eveing.
如果她今天晚上没有来，我会非常高兴。
she d be pretty if she didn t wear so much make-up.not unless she wore so much make up.
如果她没有化如此浓的妆，她会更漂亮。
