IF条件句虚拟语气
虚拟语气是一项语法难点，为了让学员们便于理解与记忆，我们把虚拟语气分成三大块来讨论：
1．名词从句中的虚拟语气标志词+should+动词原形
2．条件从句中的虚拟语气①三种基本态②倒装虚拟句③混时虚拟句④含蓄虚拟句⑤跳层虚拟句
3．其它情形中的虚拟语气（wish/would rather/It’s high time„/If only„/lest）
一．三种基本形态（1）
表虚拟的时间 if从句谓语形式主句谓语形式
现在： did / were would (should, might, could)+do
过去： had done/ had been would (should/might/could)+have done(been) 将来： were to/ should+do would (should, might, could)+do
三种基本形态（2）（这是基础，建议牢记下面的例句，争取能脱口而出）与现在事实相反：If I had enough money, I would buy a book.
与过去事实相反：If I had had enough money, I would have bought a book. 与将来事实相反：If I were to have enough money, I would buy a book. If I should have enough money, I would buy a book.
二、倒装虚拟句（只能与过去/将来事实相反，省去if，只有三种倒装形式） Had I had enough money, I would have bought a book.
Were I to have enough money, I would buy a book.
Should I have enough money, I would buy a book.
三、混合时间虚拟语气（主要是抓住时间状语）
(对过去事实虚拟+对现在事实虚拟)
If I had studied English at school, I could read the English novel now. (对现在事实虚拟+对过去事实虚拟)
If she were not so careless, she wouldn’t have made such a mistake.
四、含蓄虚拟句（在阅读中常见）
3. 虚拟语气用在主语从句中。在句型“It is important (necessary, strange, natural等) that...”中，that 后面的从句中的谓语动词用(should) + 动词原形。
It's necessary that we should have a walk now. 我们现在有必要出去散散步。
What would I have done without you?
But for their help, I would not have finished the task.
But that the doctor arrived on time that day, they would have been dead. Given more time, I would have been able to finish the test.
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