虚拟语气的构成及用法

l 相关背景知识介绍
虚拟语气 = 虚拟(假设) + 语气
Bus travel now and then (2001年版C级)
For cities without other public transport services, if all the buses were to stop running for a day, work would come to a standstill (停止) in hundreds of offices and factories and...

虚拟语气 (Subjunctive Mood)
虚拟语气是谓语动词的一种形式，用于表示非真实的假设，或表示命令、建议以及说话人的主观愿望，有时也有使语气缓和、委婉的作用。

Ⅰ、条件句中的虚拟语气
1.构成
含有条件状语从句的句子称为条件句。如果所表示的条件是真实的，或者完全可能实现的，则称为真实条件句，其主句和从句的谓语都用陈述语气，如：
You may spoil the work if you make the same mistake again.
如果条件句表示的条件根本不可能实现或实现的可能性很小时，则称为虚拟条件句，其主句和从句的谓语就要用虚拟语气。谓语形式因时间不同而有所不同。现以动词give和tell为例列表如下：

条件从句

主句

与现在事实相反的假定

gave

should + tell
would + tell

与过去事实相反的假定

had + given

should + have + told
would + have + told

推测未来不可能实现或实现可能性很小的假定

should + give
were to + give
gave

should + tell
would + tell

注：
① 在与现在事实相反的假设条件从句中谓语为be时，一般不分人称，多用过去式的复数形式were。如主语为第一、三人称单数时，也可用was (但“if I were you…”中只能用were。)
② 主句中第一人称常用should，第二、三人称常用would。但在美国英语中，第一人称也常用would。主句中除should, would外，还可用could, might。
2.用法
(1) 与现在事实相反的假定。如：
If the sun stopped radiating(放射出) heat and light, life on earth would be impossible.
如果太阳停止放射光和热，地球上的生命就不可能生存。
If I were you, I should start packing now.
如果我是你，我现在就动手收拾行装了。
(2) 与过去事实相反的假定。如：
If you had started your work earlier, you would have finished it.
如果当时你早点开始工作的话，你早就把工作完成了。
He would have succeeded in the Sydney Olympic Games if his courage hadn’t failed him.
如果他不是当时一时胆怯，他就会已经在悉尼奥运会上获胜了。
(3) 推测未来不可能实现或实现可能性很小的假定。如：
If the director came tomorrow, I would tell him about our proposal.
如果主任明天来，我将把我们的建议告诉他。
If I should live in the twenty-second century, I would spend my vacation on the moon.
如果我生活在二十二世纪，我将在月球上度假。
What would you do if war were to break out(爆发)?
如果战争爆发，你怎么办?
注：
①虚拟条件从句中，如谓语中有were (was), had, should等词，有时可把这些词放到主语前，并省略连词if。如上面(2)中的第一句(If you had started your work earlier, you would have finished it.) 和(3)中的第二句 (If I should live in the twenty-second century, I would spend my vacation on the moon.) 可分别改为下列形式而意思不变：
Had you started your work earlier, you would have finished it.
Should I live in the twenty-second century, I would spend my vacation on the moon.
②虚拟条件除用从句表示外，还可以通过介词短语等来表示，这时句中动词也用虚拟语气。如：
Without dust, there would be no clouds and no rain.
没有灰尘，不会有云，也不会有雨。
But for your cooperation, my business would have collapsed.
要不是你的合作，我经营的企业早就垮了。