「unless」的用法

「unless」跟「if...not」的意思是一樣的。就如 if 一樣,unless 後面接的是現在式、過去式或過去完成式(但絕對不是條件式)。unless 用來取代所有類型條件句的 if...not。對於使用 unless 的句子,子句順序的擺放並沒有多大的影響。

第一類條件句:unless + 現在式
if 子句 意思相當的 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.
第二類條件句:unless + 過去式
用 if 子句 意思相當的 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.
第三類條件句:unless + 過去完成式
if 子句 相當的 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.