「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。

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.

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.

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.