虚拟语气被普遍认为是难度大，不易掌握的语法项目，很容易使人望而生畏，能否从中找出一些规律呢？下面就是根据虚拟语气的谓语动词变化，把虚拟语气分为四大类型，以便掌握。

l. 时间选择型

当虚拟语气用来表示一种不能成为现实、不真实的情况时，须选择与现在、将来和过去情况相反的三种不同时间，从而决定谓语动词。这类虚拟语气主要用于如下几方面:

（1）虚拟条件句（含蓄虚拟条件句）
If l were you, l would study much harder．（与现在情况相反）
If he did（were to do，should do）it，he would do it well．（与将来情况相反）
I wouldn't have finished the work without your help． （与过去情况相反）

（2）由 even if (though) 引导的让步状语从句，其谓语动词变化同于虚拟条件句，在口语中也可用直陈语气。

Even if he were here, he wouldn't be able to help you． （与现在情况相反）
Nothing could have saved your father，even if the doctor had arrived on time．（与过去情况相反）

（3） wish后的宾语从句

I wish I were five years younger than you．（与现在情况相反）
He wishes you would go with him.（与将来情况相反）
I wished I had won the match．（与过去情况相反）

注意：wish的时态不影响从句三种时间的判定。

（4） as if (though)引导的表语从句和方式状语从句
He looks as if he were very sleepy．（与现在情况相反）
They are talking about something, as if they were quarrelling with each other．

2．should+动词原形型

这种类型的虚拟语气一般用于主语从句、宾语从句、表语和同位语从句。谓语由should+动词原形构成，无论什么人称都不能用 would, should在口语中可以略去。

（1）在主语从句中用以表示惊奇、惋惜、理应如此，构成 It is natural （important, necessary, strange, a pity, a shame等）that… 句型。
It is natural that you should say apology to him．
It is a pity that you should be careless．

（2）用于表示命令、建议一类动词后的宾语从句，如：suggest，move，insist，demand，request，command等。
The young man insisted that he should be sent to do the work．
I suggested that we should set off earlier．
应注意：当insist表示对已发生过的事物的看法，或当suggest为“说明了”，“

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