「unless」的用法

「unless」跟「if...not」的意思是一样的。就如 if 一样,unless 后面接的是现在时丶过去时或过去完成时(但绝对不是条件式)。unless 用来取代所有类型条件句的 if...not。对于使用 unless 的句子,子句顺序的摆放并没有多大的影响。

第一类条件句:unless + 现在时
if 子句 意思相当的 unless 子句
You will be sick if you don't stop eating. You'll be sick unless you stop eating.
I won't pay if you don't provide the goods immediately. I won't pay unless you provide the goods immediately.
If you don't study dilligently, you'll never understand trigonometry. Unless you study dilligently, you'll never understand trigonometry.
第二类条件句:unless + 过去时
用 if 子句 意思相当的 unless 子句
If he wasn't very ill, he would be at work. Unless he was very ill, he would be at work.
I wouldn't eat that food if I wasn't really hungry. I wouldn't eat that food unless I was really hungry.
She would be here by now if she wasn't stuck in traffic. She would be here by now unless she was stuck in traffic.
第三类条件句:unless + 过去完成时
if 子句 相当的 unless 子句
Our director would not have signed the contract if she hadn't had a lawyer present. Our director would not have signed the contract unless she had had a lawyer present.
I wouldn't have phoned him if you hadn't suggested it. I wouldn't have phoned him unless you'd suggested it.
They would have shot her if she hadn't given them the money. They would have shot her unless she'd given them the money.