英语中虚拟语气的用法很多。在英语教学的过程中，我们常常发现有些学生对各种虚拟语气结构中的动词是用现在虚拟式还是过去虚拟式分辨不清，下面我就这个问题作一一说明。
1．表示有可能实现的意愿的虚拟结构中，动词常用现在虚拟式：
（1）It is + adj + that +Sb + do/be + Sth
该结构中的主语从句表示说话人的意愿或主观态度，结构中的形容词用来表现说者的意愿趋向, 从句中的动词应用现在虚拟式。可用于该结构中的形容词包括 advisable, appropriate, crucial, desirable, essential, fitting, imperative（必要的）, important, impossible, natural, necessary, obligatory（必须）, preferable（更好的）, proper, sad, strange, surprising, vital（至关重要的）等。
如：It is necessary that the car be checked thoroughly.
It was important that she have confidence in herself.
（2） S1 + v + that S2 + do Sth
在带有宾语从句的英语句子中，如主句中的谓语动词表示以下有可能实现的意愿时，从句中的动词应用现在虚拟式：
<1> 要求: ask, beg, demand, insist, request, require,
<2> 建议: advise, advocate, propose, recommend, suggest
<3> 命令: command, direct（命令, decree（裁决）instruct, move, order, urge, stipulate。
<4> 愿望: desire, expect, prefer（宁愿）。
<5> 决定：decide。
如：He insisted that you be on time.
It is desired that we get everything ready by tonight.
The commanding officer decided that no one be admitted without a special pass.
（3）N+(…) that +sb +do sth
表示要求、建议、命令、愿望、决定等意义的名词后如有其同位语从句或表语从句时，这类从句中的动词应用现在虚拟式。适用于该句型的名词有advice, conviction, decision, decree, demand, idea, motion, necessity, order, plan, preference, proposal, recommendation, requirement, resolution (决议), suggestion, wish。
如：My idea is that we go right now.
The resolution that women be allowed to vote was carried.
（4）Fear/be afraid/worried lest Sb do Sth 表示害怕(担心)某种可能出现的情况，从句中的动词应用现在虚拟式。
如: I fear lest he arrive too late.
We were afraid lest it be stolen.
He was at once worried lest she leave him.
2．在用来表示不太可能实现的意愿或假设的虚拟结构中，动词常用过去虚拟式：
（1）Would that sb did sth/ had done sth
该结构表示与现实相反的愿望（would充当及物动词），that从句中的动词应用过去虚拟式。
如：Would that I were a student again.
Would that you didn't refuse my proposal of marriage（求婚）.
Would that I had told him the change last Friday.
（2）If only
If only有两种主要用法:
① 表示目前较难实现的愿望或与过去事实相反的愿望。表示目前较难实现的愿望时使
If only Sb+ did/were Sth 或 if only Sb could/would do/be Sth的结构；表示与过去事实相反的愿望时使用if only Sb had done/been Sth 或 if only Sb could have done Sth的结构。
如：Oh, if he could only come
If only you would listen to reason.
If only I could have gone to the movies.
If only you hadn't told Linda what I said.
② if only 还可带一个条件状语从句，该条件句表示一种较难兑现的条件。
如：If only you would help me type my paper this afternoon, I would not have to burn the midnight oil.
If only they were here now, we would be able to discuss the issue together.
（3）But for和Except for（若非）
but for 和except for均需置于句首，其后均可接名词短语，表示与事实相反的假设或条件，其后句子中的谓语要用should/would/could (not)do/be…来表示对现在的虚拟；而用should/would (not) have done/been… 来表示对过去的虚拟。
如：But/Except for air and water, nothing could live in the earth.
But/Except for the storm, I could have swam across the Channel.
But/Except for Martin's arms, I would have collapsed.
(4) but that（若非）
But that 后接真实情况的条件从句，该从句不用虚拟式，可置于句首或句中，而主句则需用 虚拟式Sb would (not) have done Sth（对过去）。
如：But that he was prevented, he would have shot the other gay.
He would have said no but that he was afraid.
（5）If引导的非真实条件句
在If 引导的非真实条件句中，if Sb did/were sth表示对现在或将来的虚拟，这时主句用would do sth/would be doing sth来表示现在或将来难以实现的愿望或假设；if Sb had done/been sth表示对过去的虚拟，这时主句用could/might/should/would have done/been sth来表示过去未能实现的愿望或假设。如果省去条件句中的if，则引起该条件句的倒装。
如：If I were you, I'd marry her.
If we were men, we'd be doing something decent now.
Had he come earlier, he would have met her.
I should have talked to mother if I had thought of it.
（6）if it were not / had not been for…
该结构也是由if引导的非真实条件句，其中if it were not for…是与现在事实相反的条件句（句中的were不可替换成was），意为"要不是…"，这时主句中的动词使用过去将来式；if it had not been for…是与过去事实相反的条件句，这时主句中的动词使用过去将来完成式（另外，该条件句中的if如被省去时则引起倒装）。
- 考试辅导
