1.主从句谓语动词的时态
(1)掌握主从句谓语动词的规范搭配:
主句从句
与现在事实相反would/情态动词过去式+do were (不分人称)/did
与过去事实相反would/情态动词过去式+have done had done
与将来事实相反would/情态动词过去式+do should do / were to do
如：If the doctor had been available, the child could not have died.
There is a real possibility that these animals could be frightened, should there be a sudden loud noise.
(2)区分主从句表示的不同时间概念：
主从句谓语动词所指时间不同，这叫做错综时间条件句，动词形式应根据实际情况来调整。如：
Had it not been for the timely investment from the general public, our company would not be so thriving as it is.
(主句与现在事实相反，从句与过去事实相反)
Had Paul received six more votes in the last election, he would be our chairman now.
(主句与现在事实相反，从句与过去事实相反)
(3)识别事实和假设混合句：
Your math instructor would have been happy to give you a make-up examination had you gone and explained that your parents were ill at the time. (句子前半部分为假设情况，而“父母病了”是事实)
I would have gone to visit him in the hospital had it been at all possible, but I was fully occupied the whole of last week. (前半部分为假设，后半部分是事实)
2.名词性从句的虚拟形式
名词性从句是指宾语从句、主语从句、表语从句和同位语从句。从句的谓语动词需用(should+)动词原形表示虚拟。考生应熟悉：
(1)下列动词做谓语时，that宾语从句中的动词用虚拟形式：
desire, advise, recommend, command, direct, order, ask, demand, request, require, insist, maintain, move, propose, prefer, urge, vote。如：
In the past men generally preferred that their wives work in the home.
I move that he be discharged for his serious mistake.
(2)下列形容词和分词做表语或补语时，that主语从句中动词用虚拟形式：
advisable, desirable, insistent, preferable, urgent, appropriate, compulsory, crucial, essential, imperative, important, necessary, obligatory, possible, probable, proper, vital, advised, arranged, commanded, demanded, desired, ordered, proposed, recommended, requested, required, suggested。如：
The board deem it urgent that these files should be printed right away.
It is essential that all these figures be checked twice.
(3)下列名词接同位语从句或表语从句时，从句中动词用虚拟形式：
insistence, preference, recommendation, suggestion, proposal, motion, desire, requirement, request, order, necessity, importance, regulation, rule, resolution, understanding。如：
John Wagner’s most enduring contribution to the study of Afro-American poetry is his insistence that it be analyzed in a religious, as well as worldly, frame of reference.
They keep telling us it is of utmost importance that our representative be sent to the conference on schedule.
3.含蓄虚拟条件句的谓语动词形式
含蓄虚拟语气是指假设条件不通过if从句表达，而是暗含在其他结构中。考生应熟悉：
(1)连词but, but that, or, or else；副词otherwise, unfortunately等表示转折假设。如：
A safety analysis would have identified the target as a potential danger. Unfortunately, it was never done.
Victor obviously doesn’t know what’s happened; otherwise he wouldn’t have made such a stupid remark.
(2)介词短语暗含假设条件，常用的有：without, but for, under more favorable conditions等。如：
But for the English examination I would have gone to the concert last Sunday.
(3)intended/meant/hoped/wished/plann或was/were +不定式完成式或had intended/meant/planned/hoped/wished
+不定式一般式暗示虚拟语气。如：I intended to have called on you, but I was busy at that time.
(4)情态动词完成式暗示虚拟语气。如：I should have called to make an airline reservation, but I didn’t.
4.常用虚拟形式的句型
(1)从句中动词用过去式或过去完成式表示虚拟的句型：
would rather would as soon as though suppose…
had rather would sooner as if supposing…
If only… It is (high) time that…(从句中动词只用过去式)
如：His wife would rather they didn’t talk about the matter any more.
I’d rather you went by train, because I can’t bear the idea of your being in an airplane in such bad weather.
If I were in a movie, then it would be about time that I buried my head in my hands for a cry.
My father always talks as though he were addressing a public meeting.
(2)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)相当于but for。如：
If it had not been for his help (= but for his help), we would not have succeeded.
(3)If only…谓语动词视情况选用适当的形式。如：
If only the committee would approve the regulations and put them into effect as soon as possible.
(4)lest/for fear that/in case从句谓语用(should+)动词原形。如：
The mad man was put in the soft-padded cell lest he injure himself.
(5)whether…or…有时谓语用be的原形，引导让步虚拟从句，这种用法经常采用倒装结构。如：
Church as we use the word refers to all religious institutions, be they Christian, Islamic, Buddhist, Jewish, and so on.
The business of each day, be it selling goods or shipping them, went quite smoothly.
