四、虚拟语气(Subjunctive Mood)
虚拟语气用来表示说话人的愿望、请求、意图、建议、怀疑、设想等未能或不可能成为事实的情况，以及在说话人看来实现的可能性很小的情况。
1. If 条件句中的虚拟语气
If 非真实条件句所表示的假设是不可能或不大可能发生或实现的，句中的主句与从句都用虚拟语气，其构成如下：
从句 | 主句 | |
与现在事实相反 | 动词的过去式(be为were) | would (should, could, might) + 动词原形 |
与过去事实相反 | had + 过去分词 | would (should, could, might) + have + 过去分词 |
与将来事实可能相反 | 动词过去式（should + 动词原形， were to + 动词原形） | would (should, could, might) + 动词原形 |
例句：
If I had time, I would go to the movies with you.
If we hadn’t made adequate preparations, the conference wouldn’t have been so successful.
If it were to rain tomorrow, the game would be put off.
几种特殊形式：
1)在非真实条件句中，有时从句的动词所表示的动作和主句的动词所表示的动作并不同时发生，在这样的条件句中使用的虚拟式称为混合虚拟式。其构成视具体情况而定。例如：
If I had taken my raincoat when I came out this morning, I would not be wet now.
If I were you, I wouldn’t have missed the film last night.
2)引导非真实条件从句的连词if在正式文体中有时可以省去，were, had, should等非行为动词这是应提到从句句首。例如：
If I were you, I wouldn’t feel sorry.
Were I you, I wouldn’t feel sorry.
3)不用if引导的虚拟条件句时，without, but for, but that, otherwise等同样表示虚拟。例如：
But for your help, they couldn’t have succeeded.
She wasn’t feeling well. Otherwise, she wouldn’t have left the meeting so early.
2. 其它的虚拟语气形式
1)意为“提议、建议、请求、命令”等意思的动词所带的从句(包括宾语从句和主语从句)中，谓语部分用(should +) 动词原形形式。词类动词有：ask, advise, agree, arrange, beg, command, decide, demand, desire, determine, direct, instruct, insist, intend, maintain, move, order, persuade, pray, propose, recommend, request, require, suggest, tell, urge, stipulate等。例如：
I suggest that we (should) go camping tomorrow.
He insisted that our laboratory reports (should) be handed in the day after the experiment was done.
It’s proposed that a committee (should) be set up to look into the matter.
表示上述意思的名词所带的表语从句或同位语从句也采用相同的虚拟语气的形式。如：
His suggestion is that we (should) go camping tomorrow.
His suggestion that we (should) go camping tomorrow is good.
注意：当suggest, insist等词不再表示“建议”或“坚持要求”的含义时，其后的从句不再用虚拟语气。当上述名词所带的从句为定语从句时也不用虚拟语气。例如：
His look suggested that he wasn’t telling the truth.
He insisted that he was right.
The suggestion that he made is good.
2)在 It is + 形容词 + that从句的句型中，that引导的主语从句中的谓语动词采用should + 动词原形形式，其中should常省略。常见此类形容词有：absurd, advisable, better, best, desirable, (un)fair, fortunate, good, imperative, important, incredible, just, natural, (un)necessary, odd, pleasant, possible, preferable, right, ridiculous, sad, silly, unusual, urgent, vital, wrong等，表示必要、应该、建议、要求、惊讶、不相信等意。例如：
It’s necessary that we (should) set out at once.
3)在lest, for fear that, in case等词引导的从句中，谓语部分用 (should +) 动词原形表示虚拟。例如：
Grown people should never say or do anything wrong before children, lest they (should) set them a bad example.
4)虚拟语气可用于wish后的宾语从句中，表示与事实相反的愿望。其表达形式一般是将谓语动词提前一个时态。例如：
I wish I had been to the concert last night.
I wish he would forgive me.
I wish I knew the spelling of the word now.
5)在would rather后面的从句中，动词也要求用虚拟语气，表示某人的愿望。其表达形式一般是将谓语动词提前一个时态。例如：
I’d rather you left tomorrow instead of today.
I’d rather you hadn’t done anything like that.
I’d rather stay at home instead of going outside.
6)在由as if, as though引导的方式状语从句中，表示和现在事实相反或对现在情况有所怀疑，或表示与主句谓语动词同时或其后的假设情况时，从句中谓语动词用过去时。表示过去想象中的动作或情况或表示在主句谓语动词所表示时间之前的假设情况，从句用过去完成时。如果表示的情况很可能发生或是事实，则用陈述语气。例如：
She looks as if she knew all about it.
They talked as though they had got acquainted with each other for years.
7)在if only引起的感叹句中，用谓语动词的一般过去时表示与现在的事实相反的情况，用过去完成时表示与过去事实相反的情况。例如：
If only he knew our telephone number!
If only I had prepared for the examination last night.
8)It is (high, about) time that…的句型要求用虚拟式，表示应该做还没有做的事。其表达形式一般是谓语动词使用过去时态。例如：
It’s high time that he stopped smoking.
It’s about time that we took our leave.
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