英语的条件句
做个小测验，检验一下学习成果条件句由 if 从句和主句组成。两个分句所用的时态表明了这种情况有多真实、多大可能发生。
四类条件句一览
记住每一类的时态搭配。if 从句可以放在前面，也可以放在后面；只有放在前面时才用逗号。
| 类型 | if 从句 | 主句 | 用法 |
|---|---|---|---|
| 零条件句 | 一般现在时 | 一般现在时 | 永远成立的事实 |
| 第一条件句 | 一般现在时 | will + 动词 | 将来真实可能发生的事 |
| 第二条件句 | 一般过去时 | would + 动词 | 现在或将来不真实或不太可能的情况 |
| 第三条件句 | 过去完成时 | would have + 过去分词 | 过去不真实的情况 |
零条件句
用于科学事实、规律和总会发生的事。这里的 if 和 when 意思相同。
If you heat ice, it melts.冰加热就会融化。
If I drink coffee at night, I can't sleep.我晚上喝了咖啡就睡不着。
Plants die if they don't get water.植物没有水就会死。
第一条件句
用于真的可能发生的情况及其可能的结果。if 从句里绝不用 will。
If it rains tomorrow, we'll stay at home.如果明天下雨，我们就待在家里。
If you study, you'll pass the exam.你好好学习，就能通过考试。不能说 If you will study。
I won't go if you don't come with me.你不跟我一起去，我就不去。
第二条件句
用于假想的情况：现在并不真实或不太可能的事。这里的过去时并不表示过去的时间。
If I had more money, I would buy a house by the sea.要是我有更多的钱，我就在海边买一栋房子。
If I were you, I'd talk to her.我要是你，就去跟她谈谈。在规范英语中，所有主语都可以用 were，特别是 If I were you 这一说法。
What would you do if you won the lottery?要是你中了彩票，你会做什么？
小测验
关于本课的5道小题，看看你能答对几道？
0 XP
第1题，共5题
请选择正确答案。
If she had studied harder last year, she ___ the exam.
第三条件句
用来设想一个不同的过去及其结果。因为过去无法改变，它常常表示后悔或责备。
If we had left earlier, we wouldn't have missed the train.要是我们早点出发，就不会误了火车。
If she had studied harder, she would have passed.要是她当时更努力学习，就能及格了。
If I'd known, I would have called you.我要是早知道，就给你打电话了。这里的 'd 是 had 的缩写；在 I'd call 中则是 would 的缩写。
unless
unless 意思是 if not（除非，如果不）。它后面的动词用肯定形式，因为否定的意思已经包含在 unless 里了。
| 用 if not | 用 unless |
|---|---|
| You won't pass if you don't study. | You won't pass unless you study. |
| We'll go if it doesn't rain. | We'll go unless it rains. |
| I can't help if you don't tell me. | I can't help unless you tell me. |
常见错误
will 和 would 几乎从不用在 if 从句里。
| 错误 | 正确 |
|---|---|
| If it will rain, we'll stay in. | If it rains, we'll stay in. |
| If I would have time, I'd help. | If I had time, I'd help. |
| If I would have known, I would have come. | If I had known, I would have come. |
| Unless you don't hurry, you'll be late. | Unless you hurry, you'll be late. |
例句
If you press this button, the machine stops.按下这个按钮，机器就会停下来。
If I see Anna, I'll give her your message.我要是见到安娜，就把你的话转告她。
We'll miss the bus unless we leave now.我们现在不走就赶不上公交车了。
If I lived near the sea, I would swim every day.要是我住在海边，我就每天去游泳。
She wouldn't be so tired if she went to bed earlier.她要是早点睡，就不会这么累了。
If you had asked me, I would have helped you.你当时要是问我，我就帮你了。
What would you have done if you had lost your passport?要是你把护照弄丢了，你当时会怎么办？