[英语语法]词法之动词:虚拟语气
本博文源于《语法知识清单》，语气和时态、语态一样，是谓语动词的一种形式，表明说话的目的和意图。英语中有四种语气：陈述语气、疑问语气、祈使语气。
语气的分类
- 陈述语气：用来陈述事实或提出想法，包括肯定与否定
- 疑问语气：用来提出问题
- 祈使语气：用来向对方提出请求、邀请、给予、忠告、指示、警告、发出命令等的语气称为祈使语气。在祈使语气中，直接用动词原形，主语you一般省略。
- 虚拟语气：在表示一种完全假设的情况或主观愿望时，动词需用一种特殊的形式。
虚拟语气在条件句的用法
条件句分为真实条件句和虚拟条件句
真实条件句
可能实现的条件句叫真实条件句，这种条件句实现的可能性非常大，在条件句中从句常用一般现在表将来，遵循主将从现原则。
- If I have time,I’ll come over to see you.
虚拟条件句
虚拟条件句则表示不能实现的或纯假想的情况，其谓语动词用虚拟语气。
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虚拟语气在条件句的其他用法
错综时间条件句(也称为“混合虚拟语气”)
有些条件句的主句谓语和从句谓语表示的动作在时间上并不一致，这类句子称为错综时间条件句。
例子:
If you had taken my advice then,you wouldn’t be in trouble now.
含蓄虚拟条件句
有些句子不含条件从句，而是通过介词或介词短语(but for,without)、上下文、连词（but、or等）或其他方式表现出来，意思和条件句差不多，这种句子称为“含蓄虚拟条件句”
例子：
Without electricity,the world would be dark.
(=If there were no electricity,the would would be dark.)
虚拟语气的倒装
如果条件句中含有were，should或had，有时可将if省略，把were，should或had,有时可将if省略，把were，should或had移到主语之前
例子：
If you had taken my advice,you wouldn’t have failed in the examination.
---->Had you taken my advice,you wouldn’t have failed in the examination.
虚拟语气在三大从句的运用
主语从句中的运用
在以下几个句型中，it是形式主语，that引导的是主语从句，谓语部分常用“(should+)动词原形”虚拟语气形式.
It be + adj. + that…常见的形容词有：important，necessary等，should意为“应该，竟然”
It is necessary that you (should) seize every possible chance.
It be + n.+that…常见的名词有：pity/shame/surprise/wonder等，should意为“竟然”
It is pity that you (should) have to leave.
It be + 过去分词 + that…常见的过去分词有：suggested/required/ordered/proposed等
It is suggested that parents (should) spend more time with their children.
虚拟语气在宾语从句中的运用
wish后的宾语从句中虚拟语气的用法
| 主句表达的愿望 | 宾语从句中谓语动词的形式 |
|---|---|
| 表示与现在事实相反的愿望 | 过去式(be用were) |
| 表示与过去事实相反的愿望 | had+过去分词 |
| 表示与将来事实相反的愿望 | would/could+动词原形 |
例子：
I wish I were ten years yonger.
would rather后的宾语从句谓语动词常用过去式，表示对现在或将来的虚拟；用“had+过去分词”表示对过去的虚拟.
Dont’t always make noise.I’d rather you kept silent.
表示“建议、命令、要求”等动词的宾语从句常用“(should+)动词原形”虚拟结构.
“一、二、四、四法”：一个“坚持（insist）”，两个“命令（order,command）”,四个“建议（suggest propose recommend advise）”,四个“要求(demand,require,request,desire)”
例子：
My parents advise I should not watch too much TV.
虚拟语气在表语从句和同位语从句中的运用
在suggestion,proposal,order,request,advice等名词(表建议、命令、要求…)后的表语从句和同位语从句中要用虚拟语气，其谓语动词构成是“(should+)动词原形”
His suggestion is that we (should) go to Dalian for sightseeing.
as if/as though引导的表语从句虚拟语气
| 对事实的假设 | 表语从句中的谓语动词 |
|---|---|
| 与现在事实相反 | did/were(一般过去时) |
| 与过去事实相反 | had done(过去完成时) |
| 与将来事实相反 | would/might/could+动词原形(过去将来时) |
例子：
He treats me as if I were a stranger.
虚拟语气在定语从句中的运用
虚拟语气可用于定语从句中。这种从句常用在It is(high)time (that)…句型中.从句中谓语动词一般用过去式或“should+动词原形”的虚拟结构
It’s time that public should raise their awareness of using shared bikes reasonably.
虚拟语气在状语从句中的运用
as if/though引导的方式状语从句所表达内容如果与实际相反或者发生的可能性不大，则从句中需用虚拟语气，形式和as if/though引导表语从句时一样
He speaks as though he were sick.
在in case,for fear that,in order that,so that 引导的目的状语从句中，谓语用“should /could/would +动词原形”
He took his raincoat with him in case / for fear that he should be caught in the rain.
虚拟语气的其他用法
表示祝愿：常用“May + 主语 + 动词原形 + 其他”结构，有时也会只用动词原形
May God bless you!
if only 句型：if only 后跟虚拟语气表示“要是…就好了”。用过去式表示与现在事实相反；用“had+过去分词”表示与过去事实相反，用“would+动词原形”表示将来事实相反
If only she would listen to me carefully.=I wish she would listen to me carefully.
表示“本打算做而未做成”：hope、want、plan、mean、intended、expect等动词的“had+过去分词”形式和这些动词的“过去式+to have done”形式都表示过去未曾实现的希望、打算、意图
I had meant to phone you,but I forgot your phone number.=I meant to have phoned you,but I forgot your phone number.