虚拟语气是常考语法内容之一，下面对其主要用法进行概括总结，以帮助学生更好地掌握。
1在非真实条件句中，主要有三种情况：a）现在虚拟（从句谓语用过去式，主句谓语用 would ＋动词原形）；b）过去虚拟（从句谓语用 had ＋过去分词，主句谓语用would ＋have ＋过去分词）；c）将来虚拟（从句谓语用过去式或should／wereto＋动词原形，主句谓语用would ＋动词原形）。上述would还可换成should（用于第一人称），could和might。例如：
I would go if I had the time．要是有时间我就会去。
I should have talked to my mother if I had thought of it．如果我想到了这件事，我就会对母亲讲的。
If I saw him tomorrow，I would phone you．如果明天我看见他，我就给你打电话。
关于非真实条件句，还应注意以下几点：
1）错综时间条件句。从句与主句时间不一致，它们应分别使用相应的谓语形式。例：
If you were in better health，we would have invited you to our picnic．如果你身体好些，我们就邀请你去野餐了。（从句为现在虚拟形式，主句为过去虚拟形式）
If the doctor had not operated on him right away，he would be dead now．（从句为过去虚拟形式，主句为现在虚拟形式）
2）含蓄条件句。虚拟条件隐含在句中。
a）用but for，but that（that从句用陈述语气），with，without，or ／otherwise等引出。例：
She came to my office yesterday；otherwise，I should not have met her．她昨天到我办公室来了。否则，我不会见到她的。（＝If she hadn't come to my office yesterday．．．）
I could not have passed the exam but for your help．若不是你的帮助，我不会通过考试的。（＝If it hadn't been for your help．．．）
But that you helped him，he would have failed．如果没有你帮助他，他本会失败的。（＝If you hadn't helped him．．．）
b）由上下文或其他方式表示。例：
He would have given you more help，but he was too busy．他本会给你更多的帮助，但是他（那时）太忙了。（隐含了If he had not been busy．．．）
That would have been considered impossible in the past．要在过去，这会被看作是不可能的。（隐含了If it had been inthepast．．．）
This same thing，happening in wartime， would amount to disaster．这种事要是发生在战时就等于一场灾难。（隐含了If it happened in wartime．．．）
3）省略if条件句。if省略而把were，had， should提到主语前。例：
Were I you，I would go abroad．我要是你，我就会出国。（＝If I were you．．．）
Had I been there，I would have helped him．我要是在那儿，我就会帮助他了。（＝If I had been there．．．）
4）主句为陈述语气的条件句。有时条件从句谓语用虚拟形式should ＋动词原形（表示实现的可能性较小），而主句用陈述语气。例：
If he should come，ask him to wait．万一他来了，让他等一下。
Should she call，what will／would I say？她要是打电话来，我怎么说呢？
2．在necessary等形容词后的从句中，谓语形式为（should ＋动词原形）。常见形容词有necessary，essential，imperative，advisable， desirable，urgent，vital，appropriate，compulsory等。例：
It is necessary that the work（should）be done at once．这项工作必须立即完成。
It is imperative that you（should）not be seen here．切记不要让人看见你在这里。
3．在suggest ／suggestion等动词／名词后的从句中，谓语形式为（should ＋动词原形）。这类词表示建议、命令和要求等，常见的有suggest ／suggestion，recommend ／recommen- dation，propose ／proposal，require ／requirement， prefer，move，insist，urge，desire等。例：
He suggested that we（should）hold a meeting．他建议我们开个会。
His suggestion that we（should）hold a meeting was reasonable．他关于我们开会的建议是合理的。
4．wish之后的从句中。若表示与现在或说话时事实相反的愿望（在时间上，wish与其后的动作同时发生），谓语用过去时态形式；若表示与已经发生的事实相反的愿望（wish与其后的动作相比，后者先于前者发生），谓语用过去完成时态形式；若表示将来不容易实现的主观愿望（有时伴有说话人不满、不快等情绪），谓语用would ＋动词原形。例：
She wishes／wished she knew how to teach English more efficiently．她希望她知道如何更有效地教英语。
I wish I hadn't stayed there．我希望我没有呆在那儿。
I wish you would turn down the radio．我希望你把收音机音量调小一点。
wish之后还有时用虚拟语气的变体形式。例：
I wish I were／was skating with her．我希望我正和她一起滑冰。（用进行体，突出正在进行）
I wish I could have slept longer this morning，but I had to get up and came to class．我希望今早能多睡会儿，可不得不起床来上课。（could have slept比had slept突出情态意义"能够"。）
5．would rather／sooner之后的从句中。与wish之后从句中的谓语形式类似，但不使用would ＋动词原形形式。例：
I'd rather／sooner you did your homework right now．我希望你现在就做作业。
I would rather／sooner you came tomorrow．我宁愿你明天来。
I'd rather／sooner you hadn't come yesterday．我倒希望你昨天没来。
6．as if ／as though之后的从句中。若从句动作／状态与主句动作／状态同时发生，谓语用过去时态形式；若从句动作／状态先于主句动作／状态发生，谓语用过去完成时态形式。例：
I've loved you as if you were my son．我爱你就好像你是我的儿子一样。
He looks as if he had seen a ghost．他看上去好像见到了鬼一样。
若是真实情况，则用陈述语气。例：
It looks as if it's going to rain．天看上去要下雨。
7．if only之后的句子中。常用于简单句，表示"但愿……；要是……就好了"。谓语动词形式与wish之后动词形式相同。例：
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