3. 混合条件句
     有时，主句与从句的动作发生在不同的时间，主句从句谓语动词的虚拟语气形式因时间不同而不同，这种条件句叫做混合条件句。例如：
If you had asked him yesterday, you would know what to do now. 如果你昨天问过他，今天就知道做什么了。
（从句与过去事实相反，主句与现在事实相反。）
If it had rained last night（过去）, it would be very cold today（现在）. 如果昨晚下过雨，今天就会很冷了。

4. 虚拟条件句的倒装
     虚拟条件句的从句部分含有were, should, 或had时, 可省略if，再把were, should或had 移到从句的句首，实行倒装。例如：
Were they here now, they could help us. =If they were here now, they could help us.他们现在在的话，就会帮助我们了。
Had you come earlier, you would have met him. =If you had come earlier, you would have met him.你来得早一点，就碰到他了。
Should it rain, the crops would be saved. =Were it to rain, the crops would be saved.假如下雨，庄稼就有救了。
注意：在虚拟语气的从句中，动词'be'的过去时态一律用"were"，不用was，即在从句中be用were代替。例如：
If I were you, I would go to look for him. 如果我是你，就会去找他。
If he were here, everything would be all right. 如果他在这儿，一切都会好的。
典型例题
_____ to do the work, I should do it some other day.
A. If were I　　 B. I were　C. Were I　D. Was I
答案C. 在虚拟条件状语中如果有were, should, had这三个词，通常将if省略，主语提前, 变成 were, should, had +主语的形式。但要注意，在虚拟条件状语从句中，省略连词的倒装形式的句首不能用动词的缩略形式。如我们可说 Were I not to do, 而不能说 Weren't I to do。

5. 特殊的虚拟语气词should
1）在主语从句中的应用
     主语从句（常用形式主语 it 来代替，结构为 It is that…）中的虚拟语气主要取决于某些用来表示建议、命令、要求、惊异和失望等的形容词和过去分词，其形式为：（should）+ 动词原形。常这样用的形容词有：appropriate，advisable，better，desirable，essential，imperative，important，insistent，natural，necessary，preferable，strange，urgent，vital等。过去分词有：desired, demanded, ordered, requested, suggested, recommended, required 等。
例如：
It is essential that you (should) win the voters’ hearts.
It was suggested that he (should) join the club activities.
2）在宾语从句中的应用
     在表示命令、建议、要求等一类动词后面的从句中，像order, suggest, propose, require, demand, request, insist, command, insist + （should） do等。例如：
I suggest that we （should） hold a meeting next week. 我建议下周召开个会议。
He insisted that he （should ） be sent there.他要求被派到那儿去。
注意：如suggest, insist不表示"建议" 或"坚持要某人做某事时"，即它们用于其本意"暗示、表明"、"坚持认为"时，宾语从句用陈述语气。
判断改错：
（错）You pale face suggests that you（should）be ill.
（对）Your pale face suggests that you are ill.
（错）I insisted that you（should）be wrong.
（对）I insisted that you were wrong.
3）在表语从句，同位语从句中的应用
     suggestion, proposal, idea, plan, order, advice等名词后面的表语从句、同位语从句中要用虚拟语气，即（should）+动词原形。例如：
My idea is that we（should）get more people to attend the conference.我的想法是让更多的人来参加会议。
I make a proposal that we（should）hold a meeting next week.我提了个建议，下周我们开个会。