「unless」的用法 | 英语文法指南 | ef-九游官网下载
「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. |