3. 虚拟语气
第一大类：非真实条件下的虚拟语气
时间 从句 主句
与现在事实相反 did/ were should/could/would + do
与过去事实相反 had done should/could/would + have done
与将来事实相反 were to doshould do should/could/would + do                           
e.g. If I were you, I would be happy to do it.
 If we had got the news, we could have prepared earlier.
 If the job were to succeed, you should work harder.

第二大类：从句中用过去时或过去完成时的虚拟语气
1) would rather + 从句
2) wish + 从句
3) if only + 从句
4) as if/ as though + 从句
5) It’s time + 从句
e.g. I would rather you didn’t tell me the story now.
 I would rather you had told me the story yesterday.

第三大类：从句中用should加动词原形的虚拟语气，其中should可省略。
1) suggest, propose, advise, move(动议), ask, order, require, request, desire, insist, prefer 等动词后接的宾语从句；
2) suggestion, proposal, advice, motion, order, requirement, request, desire, preference等名词后的同位语从句；
3) important, necessary, essential, imperative, desirable, advisable, preferable 等形容词用在it is … that…句型中；
4) lest, in case, for fear that 等引导的从句中。
e.g. It is suggested that the meeting (should) be put off.
 It is my suggestion that the meeting (should) be put off.
 It is necessary that the meeting (should) be put off.
 He came to the office earlier lest he (should) miss the important meeting.
 
历年考题中的虚拟语气
1. If it hadn’t been for your help, we ___ (be) in real trouble. He would have given you more help, if he ___ (not be) so busy.
3. It is high time that we ___ (take) firm measures to protect our environment.
4. It was imperative that students ___ (finish) their papers before July 1st.
5. They demanded that the right to vote ___ (give) to every adult person.There was a mistake on my paycheck. I _____(receive) $10 more.I would rather he ____ ( buy) the house next year.  The manager told us to be friendly to the visitors as if we ___ (meet) them before.
9. Should she come tomorrow, I ___ take her to the museum.  
[A] can    [B] will   [C] would    [D] must
10. If we ___ everything ready by now, we should be having a terrible time tomorrow.
[A] hadn’t got  [B] didn’t get [C] wouldn’t have got [D] wouldn’t get

Key:
1. would have been 与过去事实相反的虚拟语气的主句
2. had not been 与过去事实相反的虚拟语气的从句
3. took  It is high time +过去式的虚拟形式
4. should finish/finish  It was imperative that+动词原形的虚拟形式
5. be given  demand所接宾语从句用动词原形的虚拟形式
6. should have received 与过去事实相反的虚拟语气的主句，表示“本应该收到”而实际上没有。
7. bought would rather后接宾语从句，从句用过去式表示虚拟语气。
8. had met  as if 所引导的从句用过去完成式表示虚拟语气。
9. C 与将来事实相反的虚拟语气的主句。
10. A 从句与现在事实相反，但本身已经是现在完成时（从by now可以看出），所以变为过去完成时。