虚拟语气的错综复杂些体现在它在if条件句，目的状语从句，宾语从句等结构中的应用。

一. if条件句中的虚拟

if在表示“如果”的意思时，可对过去，现在和将来提出假设，表示同过去事实相反，同现在事实相反和同将来事实相反的情况。

虚拟情况	if条件句动词时态形式	主句中动词形态形式
同过去事实相反	had done	would/should/could/might + have done
同现在事实相反	did/were	would/should/could/might + do
同将来事实相反	1. did/were 2. should do 3. were to do	would/should/could/might + do

例1： The dinosaurs probably became extinct after a giant asteroid hit the Earth about 65 million years ago. But what _____ if this asteroid _______?                A

A would have happened; had missed              B. would happen; missed

C happened; would miss                                 D. was happening; missed

例2：_____ information provided by members of the public, the police would have a much more difficult job.        C

A supposing        B Provided that         C If it were not for         D On condition that

例3：There is a real possibility that these animals could be frightened, ______ a sudden loud noise.                B

A being there         B should there be         C there was         D there having been

例4：______ a serious crime, what exactly should you do ?        B

A Unless you witness         B If you were to witness

C If only you witness          D Since you witness

二. 名词性从句中的虚拟

1. 主语从句中it作形式主语，it is/was + necessary/surprising/important/proper/... + that且使用表示紧急，重要等感情色彩的形容词时，that后面的谓语动词使用虚拟，用should do形式，should可以省略。

2. It is demanded/suggested/ordered/requested/proposed/... + that且表示请求，建议，命令等，that后面的谓语动词使用虚拟，用should do形式，should可以省略。

3. 在使用suggestion，proposal，order，plan，idea，advice，decision等词的表语从句或同位语从句之后需要使用虚拟，使用should do形式，should可以省略。

4. 宾语从句中，表示“要求，建议，请求”的动词后面使用虚拟，用should do形式，should可省略。（insist, command, suggest, advise, propose, demand, ask, request, require...）

5. 宾语从句中，wish表“愿望”的时候，后面的虚拟语气要根据从句的意义来安排。

①表示与过去事实相反的愿望，结构为“主语 + wish（that）+从句主语+ had done”

②表示与现在事实相反的愿望，结构为“主语 + wish（that）+从句主语+ did / were”

③表示与将来不太可能实现的愿望，结构为“主语 + wish（that）+从句主语+ would / could do”

6. would rather + that 从句，谓语动词用过去式表示虚拟。

例1 ：The president ordered that the stadium ______ finished before the National Day but the engineer knew very clearly that it was almost impossible for it _____ in so short a time.     B

A. be; to do        B be; to be done         C should be; to be doing         D will be; to have done

例2：I wish I ______ myself better in English, but I _____.        B

A will express; won't        B could express; can't

C would express; won't         D can express; can't