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条件从句是比较advanced的英语语法点。通常条件句分为真实条件句和虚拟条件句。前者要使用直接陈述的方式表达,后者则要使用虚拟语气。一般来说,当一个从句所表达的条件是有可能实现的、有可能是真实的条件时,用真实条件句;如果一个从句所表达的条件是不可能实现的、与客观事实完全相反的条件时,则使用虚拟条件句。对应这两大类条件句,英语中把条件句进一步细分为4种条件句形式:
1. Zero conditional
2. First conditional
3. Second conditional
4. Third conditional
条件句的结构一般由if 引导出某种假设,再由主句表示基于这种假设下的反馈。可以这么说,如果没有时态的变化,条件句并不难,但是英语中的条件句分为真实和非真实,才使得conditional成为一个很难被轻易攻克的语法点。
The reason I listed it as one of most challenging parts of English learning is it can be pretty confusing to decide which conditional form best fits your situation, and then to formulate it properly.There are four types of conditional forms:
Zero conditional 零条件从句
zero conditional 是最简单的一种 if 条件从句,因为它只涉及现在时态。一般来说零条件从句是用来描述一个真是存在的情况or表述一个自然现象的。这种从句的基本格式是:
if + present simple, then + present simple 在日常口语中我们也可以用 when 来代替 if
Examples:
1. If you study hard enough, you usually get good scores.
2. When it rains, the ground gets wet.
3. I get spooked if I see a snake.
4. If you decide to study in the USA, you must passTOEFL
总结,zero conditional是用来表述常态的,所以永远都用现在时。
First conditional 第一条件句
第一条件句是用来描述一个非常可能要发生的事情(如果要量化的话大概是99.99%),因此和零条件句一样(100%),这两种条件句都不会用到虚拟语气。first conditional的句式结构是:
if + present simple, then+ future simple
从这个结构可以看出,zero 和 first conditional 从句的区别在于后半句将一般时改成了一般将来时。有些同学在看过零条件从句例子后通常会问为什么不能把句中的现在时改成将来时,事实是当然可以改了。
无论是用 zero 还是 first conditional 都是对的,只不过用来表达不同的语境。zero conditional表达一个永远都是真实的 or 常态性的情况,而 first conditional 虽然表达相似的意思,但是通常用来描述一个一次性or特殊但真实的情况。
Examples:
1. If I see a snake I will get spooked. 如果我看到一条蛇,我会被吓到的。
如果把这个例子改成零条件从句,If I see a snake, I usually get spooked. 意思差不多,只是这句用来表达一般性的状态。
2. If you don’t go to bed on time, you’ll have trouble waking up.
3. If he doesn"t give up smoking, he"ll get sick.
Second conditional 第二条件句
从这里开始条件句开始变得 tricky了,因为第二和第三条件句都要使用虚拟语气。second conditional 是用来表述一个只在理论上可能存在的情况,or 一个假设的情况。我喜欢称这种条件句为 daydreaming conditional。它的基本句式结构是:
If +past simple (过去一般时) , then + would + verb
或者 If +past continuous (过去进行时), then + would + verb
if 可以引导过去式 and 过去进行时,另外 would 可以替换成 could, might
Examples:
1. If I won the lottery I would buy a big yacht. 如果我中了彩票我会去买个游艇。(daydreaming right?)
2. If I was still working in downtown London, I would commute by train. 如果我还在伦敦市中心上班,我就是每天乘火车去。
3. If I had some bread, milk and eggs, I could have made some French toast for you.
4. If I spoke to her directly, I might be able to persuade her. 如果我能和她直接交谈,我也许能说服她。
第二条件句有一种特殊的形式“If I were you”, 这个形式通常是在给别人意见时用。
5. If I were you, I would look for a new job.
Third conditional 第三条件句(和第二条件句一样,也要用虚拟语气)
这种条件句可以用来表达 alternative outcomes of past events。有点木已成舟无法挽回的意思。句式结构是:If + past perfect (过去完成时), then + would +present perfect (现在完成时)
Examples:
1. If I hadn’t missed the bus, I would have gotten to school on time. (隐含意思: I did miss the bus, and I was lateto school.) 如果我没有错过汽车,我就不会上课迟到了。
2. If she hadn"t been ill, she would have gone to the party. 如果她没有生病,就会去参加那个聚会了。
3. If my girlfriend had been free yesterday, I would have asked for a date. 如果我女朋友昨天有空,我就会要求她跟我约会。
补充一点:Mixed conditional 指将两种以上的条件从句在同一个对话中混用
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