1. 零条件（普遍真理）：If + 一般现在时, 一般现在时。If you heat ice, it melts.
2. 一条件（将来可能）：If + 一般现在时, will + 动词原形。If it rains, we will stay home.
3. 二条件（现在/将来虚拟）：If + 一般过去时, would + 动词原形。If I were you, I would go.
4. 三条件（过去虚拟）：If + had done, would have done。If I had known, I would have helped.
5. 混合条件：从句过去 + 主句现在。If I had studied harder, I would be rich now.
6. 关键：if 从句用现在时表将来，不能用 will（不说 If it will rain）。
7. unless = if not：Unless you run, you'll miss it.
8. 主句可换 should/could/might：If I knew, I would/could help.
9. 真实条件句里 when/as soon as 也用现在时表将来。
用法速查：规则与例句对照
类型
假设时间
if 从句
主句
例句 (en) / 中文
零条件
永远成立的真理
一般现在时
一般现在时
If you heat ice, it melts.（加热冰就融化）
一条件
将来可能发生
一般现在时
will + 动词原形
If it rains, we will stay home.（下雨就待家）
二条件
现在不太可能 / 与事实相反
一般过去时（be 用 were）
would + 动词原形
If I were you, I would buy it.（我是你就买）
三条件
与过去事实相反（后悔）
had + done
would have + done
If I had left earlier, I would have caught the train.
混合条件
过去条件 → 现在结果
had done
would + 动词原形
If I had taken the job, I would be in Paris now.
二条件里的 were（虚拟）
说法
例句
正式 / 标准：所有人称都用 were
If he were taller, he would be a basketball player.
口语：第三人称也可用 was（非正式）
If I was you…（口语可接受，考试用 were 更稳）
高频条件句速记
英文例句
中文
If you heat ice, it melts.（零）
加热冰就融化。
If it rains, we will stay home.（一）
下雨就待家。
If I had money, I would buy a car.（二）
有钱我就买车。
If I were you, I would say sorry.（二）
我是你就道歉。
If I had run faster, I would have won.（三）
跑快点就赢了。
If she had studied, she would have passed.（三）
学了就过了。
If I had left early, I would be there now.（混合）
早走现在就到了。
Unless you hurry, you'll be late.（=if not）
不快点就迟到。
考点清单（FCE）
考点
常见考法
四种条件句辨认
根据句意选结构
if 从句不加 will
改错将来时 will
If I were you
be 动词虚拟用 were
三条件 would have done
补全后悔句
混合条件句
过去条件影响现在
unless = if not
句型转换
wish / if only
与条件句联动
倒装条件句
Had I known…（拔高）
易混点辨析
表达
区别
if / unless
unless = if not
will / would
一条件主句 will；二条件主句 would
were / was
虚拟条件用 were，不用 was
if + 现在 / if + will
if 从句不出现 will
would do / would have done
现在虚拟 vs 过去虚拟
mixed condition
过去条件 + 现在结果
supposing / suppose
Supposing it rains, what then?
provided that
Provided you go, I'll go.
as long as
As long as you try, it's OK.
wish + would
I wish you would stop smoking.
if 省略倒装
Had I known, I would've helped.
but for
But for you, I would've failed.
例句精讲
If you boil water, it turns into steam.
把水烧开，它就变成蒸汽。（零条件：客观规律）
If I had more money, I would travel around the world.
要是我钱更多，我就环游世界。（二条件：与现在事实相反，我现在钱不多）
If she had studied medicine, she would have become a doctor.
要是她当初学了医，她就当医生了。（三条件：与过去事实相反，实际没学医）
防坑三则① if 从句不能出现 will：一条件里「如果明天会下雨」要说 If it rains tomorrow，不说 If it will rain。 ② 二条件里 be 动词一律用 were（If I were you），考试写 was 算错。 ③ 三条件主句一定是 would have + 过去分词，别漏 have：would have caught，不是 would catch。
补充对照
时间与事实对照表
类型
事实真相
虚拟程度
零条件
永远成立
真实，不虚拟
一条件
将来可能发生
真实，不虚拟
二条件
现在不是这样
半虚拟 / 不太可能
三条件
过去已经那样了
纯虚拟，无法改变
混合条件
过去的事影响现在
跨时间虚拟
中国学生高频错误诊断
错误 1：if 从句用 will ✗ If it will rain tomorrow… → ✓ If it rains tomorrow… if 从句用现在时表将来。
错误 2：二条件 be 用 was ✗ If I was you… → ✓ If I were you… 虚拟条件所有人称都用 were。
错误 3：三条件主句漏 have ✗ If I had left, I would catch the train. → ✓ …I would have caught… 过去虚拟主句 = would have done。
记忆口诀
三句口诀① 真理和可能是真实条件，虚拟是「与事实相反」。② if 从句永远不加 will，二条件 be 全用 were。③ 三条件标配 had done 对 would have done，一听就是后悔。
口语跟读：说出来才算会
跟读 · 互译练习
一条件：If I have time, I will call you.
二条件：If I were rich, I would travel the world.
三条件：If I had studied harder, I would have passed.
挑战：说一个你「要是当初……就好了」的三条件句子。
自测三题（点击按钮对答案）
basic填空：If it ___ (rain) tomorrow, we will cancel the picnic.（一条件）
rains。if 从句用一般现在时表将来，主语 it 加 s。
mid填空：If I ___ (be) you, I ___ (tell) her the truth.（二条件）
were, would tell。二条件虚拟，be 用 were，主句 would + 动词原形。
hard填空：If he ___ (drive) more carefully, he ___ (not have) the accident yesterday.（三条件）
had driven, wouldn't have had。与过去事实相反：if + had done，主句 would have done。
费曼三问：用你自己的话讲清楚
用你自己的话回答这三问① 零条件和一条件长得像，怎么区分？② 为什么二条件里 If I were you 用 were 不用 was？③ 三条件为什么总是带着「后悔」的味道？举一个你自己的三条件例子。
7 天复习计划
天
任务
自检
第 1 天
背零/一/二/三条件结构表
四种结构分得清
第 2 天
练二条件 If I were you 5 句
be 都用 were
第 3 天
练三条件后悔句 5 句
would have done 不漏
第 4 天
重做自测 + 混合条件句
if 从句无 will
第 5-7 天
用四种条件各说一个生活句
时态不倒退错
第 6 天
重看思维导图与必背卡
能默写出核心公式
第 7 天
不看笔记做 3 道自测 + 错题本
正确率 90% 以上
本课一句话总结
零一真实，二三虚拟：if 从句不加 will，二条件 be 全用 were，三条件 would have done 收尾。