一、非真实条件句中的虚拟语气
1.和现在的事实相反
从句：一般过去时（were/done）；主句：过去将来时（would do）
E.g.：I am not free today. If I ___ free today, I __ and visit some of my friends.
2.和过去的事实相反
从句：过去完成时（had done）；主句：过去完成时（would have done）
E.g.：If my lawyer ___ here last Saturday, he __ me from going.
3.和将来的事实相反
从句：①were to + 动词原形 ②should+动词原形 ③动词过去式；
主句should/would/could/might+动词原形
E.g.：If I were to see Tom, what ___ you ___ me to tell him?
二、宾语从句中的虚拟语气
1.wish后面宾语从句中的虚拟语气，表示与事实相反的愿望。其表达形式一般是将从句的谓语动词退后一个时态。例如:
1)与现在事实相反: wish + (that)+ did(were)
E.g.：I wish I were as healthy as you.
E.g.：I wish that I had a plane.
2)与过去事实相反 : wish + (that)+ had done
E.g.：I wish I had been to the concert last night.
E.g.：I wish you had written to him.
3)与将来事实相反 : wish + would/could/might + do
E.g.：I wish he would forgive me.
2. 在某些动词后的宾语从句中需用should+动词原形的虚拟语气形式。“should”可以省略。
一个坚持insist; 两个命令order,command ; 三条建议suggest , advise, propose;
四项要求demand, request,require, ask; 另外有:prefer、recommend
注意: suggest表“暗示表明”时 insist表“坚持认为”时不用虚拟语气
E.g.：He ordered that the students (should) wash the clothes every week by themselves.
E.g.：The doctor suggested that she (should) have an operation at once.
*His face suggested that he had been punished by the teacher.
三、主语从句中的虚拟语气
1. Itbe+过去分词+that…+(should)+动词原形+…
过去分词：suggested, requested, ordered,proposed
E.g.: It is required that nobody (should) smoke here.
E.g.: It's suggested that everybody (should) buy a dictionary
2. It be+形容词+that…+(should)+动词原形+…
形容词:important, necessary, natural,right, wrong, better, proper, funny, strange, surprising…
E.g.: It is necessary that we(should ) have a walk now.
E.g.: It's important that we(should) take good care of the patient.
3. It be+名词（ a pity/a shame/ no wonder） that…+ (should)+动词原形+…(表示惊异、懊悔、失望等情感)
It is a regret that he (should)miss this golden chance.
四、表语从句、同位语从句中的虚拟语气
在 suggestion, proposal, idea, plan, order, advice,decision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。
E.g.: My suggestion is that we(should) leave at once.
E.g.: I make a proposal that we(should) hold a meeting next week.
五、状语从句中的虚拟语气
1、用在由as if, as though引导的状语从句中，表示和现在事实相反或对现在的怀疑，用过去时；表示过去想象中的动作或情况，用过去完成时;表示将来用would + 动词原形。
E.g.: It seems as if the man were his brother.
E.g.: This device operated as though it had been repaired.
2.用在lest,for fear that和in case引导的状语从句中，这时谓语动词用(should)+动词原形
E.g.: She closed the windows lest she catch cold.
六、其他句式
1、It's(high/low) time 从句：
It is (high) time that从句谓语动词要用过去式或用should加动词原形，但should不可省略。
E.g.: It is time that the children went to bed.
E.g.: It is high time that the children should go to bed.
2、一些介词短语
But for your help, we couldn't have succeeded.
Nothing could live without the sun.
3、比较if only与only if
only if 表示“只有”；
I wake up only if the alarm clock rings.
if only 则表示“如果……就好了”。其从句中的谓语动词用过去时或过去完成时。
If only I knew more.
If only the alarm clock had rung.
七、虚拟语气难点
1、错综虚拟与隐含虚拟
错综虚拟：If you hadn't bought the ticket last week, how would you go now?
隐含虚拟：情境中提供虚拟语气
Suppose there were no gravity,objects would not fall to the ground when dropped.
She wasn't feeling very well.Otherwise she wouldn't have left the meeting so early.
He telephoned to inform me of your birthday, or I would have known nothing about it .（连词）
I might have given you more help, but I was too busy .（连词）
Given more time, we could have done it better .（分词短语）
… … Such mistakes could have been avoided .（通过上下文）
2、倒装
① Were it (=If it were) not for their help, we couldn't have got over the difficulties.
② Had I (=If I had) known about it, I would have told you.
③ Should anyone (=If anyone should) call, please take a message.
