虚拟语气是一种动词形式，表示说话人的一种愿望，假设，怀疑，建议等含义，虚拟语气所表示的含义不是客观存在的。
一．在非真实条件句中
虚拟条件句（if从句） 主句
与现在事实
相反 主语 + 主语 + would/could/might/ should + do
与过去事实
相反 主语 + 主语 + would/could/might/should + have done
与将来事实
相反 ①主语 + did
②主语 +were to do
③主语 + should do 主语 + would/could/might/should + do
1 If I were you, I would buy it. 2 If she knew English, she would ask me for help now.
3 If you had got up earlier, you would have caught the train yesterday.
注意：错综时间条件句：从句和主句发生的时间不一致时，动词的形式要分别根据它所表示的不同时间作相应的调整。 5 If you had followed my advice (听从)yesterday, you would be better now.
6 If they had studied hard in the past, they would do it easily now.
二 省略if的情况: 虚拟条件句中含were , should, had 时，可省略if,把这几个词置于句首。
1 Were I you, I wouldn’t do that. （be） 2. Had you come earlier, you would have seen him.
3. Should it rain tomorrow, I would stay at home.
三 含蓄条件句 :使用with, without, but, or,or else, otherwise， but for(= if it were not for…与现在事实相反；if it had not been for…与过去事实相反)等代条件句。
1 We couldn’t have succeeded without your help.(没有你的帮助)
2 But for the rain（要不是） we would have finished the work.
3 He telephoned to inform me of your birthday. or (=If he hadn’t telephoned to inform me of your birthday)I would have known nothing about it.
但是： If it were not for the fact that she ____sing, I would invite her to the party. C
A. couldn’t B. shouldn’t C. can’t D. mightn’t
四 常用虚拟语气的句型
(一) 在下列句型中，常用“should + 动词原形”且should可以省略：
1 表示要求，建议，命令，提议，意愿等的主语从句，宾语从句，表语从句和同位语从句中。
一坚持insist; 二命令order, command; 三建议suggest, advise,propose; 四要求demand,require,request,ask等后。
注意：当suggest作__________讲，insist作_________讲，后边that从句不用虚拟语气。
2 在It is + 形容词(necessary, natural, strange, etc. ) + that从句中。
在It is/was a pity（a shame, no wonder, etc. ） + that从句中。
1）We all agreed to his suggestion（that）we (should abandon the plan. 放弃那个计划.
2) It is suggested that the meeting should be put off next week.（被推迟）
3) It’s necessary/important/natural that we_______________________每天打扫房间.
但是1) Mike insisted that he had never stolen anything. （从未偷过）
2) The look on his face suggested that he was angry.
但是： It is（high/about）time（that）sb.did sth /should do sth
Eg: It is high time we started / should start. 动身出发
(二) 用动词的过去式表示与现在事实（或将来事实）相反，用动词的过去完成式表示与过去事实相反的句型。
1)．wish后that引导的宾语从句中。(表示对将来的设想，用could/would/might+v.)
2)．as if（though）引导的表语从句或方式状语从句中。
3)．would rather后的宾语从句中。
4)．If only引导的感叹句中。
1 I wish I _______________________. 和你一样聪明。
2 I wish he ______________________ tomorrow. 再次尝试
3 He looks as if/though he ____________________. 他是一个艺术家
4 I’d rather you _________________ there yesterday. 不去
5 Look at the terrible situation I am in! If only I _______________ (follow) your advice.