分词，主句用would / should / could / might + have +过去分词。

If he had known your address yesterday, he would have telephoned you.

3. 虚拟将来时是表示对将来实现的可能性很小的或不确定的假设。If从句的谓语形式用一般过去式或用were to / should +动词原形，主句用would / should/could/ might +动词原形。

4. 省略if 采用倒装语序的条件句。有时可以把含有助动词、情态动词、be或have的虚拟条件句中的连词if省去，而将had , should, were 等词提到主语之前，即用倒装结构。

Had he worked harder, he would have got through the exams.

Were he to leave today, he would get there by Friday.

Were I in your place, I wouldn't do that.

5混合虚拟语气

有时主句和从句的谓语动词指不同的时间，这时需要用混合虚拟语气。一般来说，在这种情况下，主从句谓语动词指代的时间不同，所以我们又可以错综时间条件句，在这种虚拟情况，动词形式应根据实际情况灵活使用，在做这些题目时候尤其要注意每道题目的提示语：时间状语。绝大多数情况下，从句或者主句都有相关的时间状语，这是我解题的关键。

If you _____ that late movie last night, you wouldn't be so sleepy.

A. haven't watched B. didn't watch

C. hadn't watched D. wouldn't have watched 答案选C。

Had Paul received six more votes in the last election, he would be our chairman now.

混合虚拟语气还有一种情况就是事实和虚拟假设的混合句，这样的句子不仅仅是时间的不同，而重要是事实和假设的混合。

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.

该句前半部分是假设虚拟，而后半部分是事实的陈述。

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.

该句前半句用的是假设虚拟，后半句主句也用的是假设虚拟（如果你去并且解释的话），但是后半句的从句用的是事实语气，因为"父母病了"是客观事实，故不需要用虚拟形式had been。

6. 含蓄虚拟条件句

含蓄条件句是指句中没有明显的虚拟条件句，而是利用其他手段来暗示存在虚拟条件。但是这类隐含式虚拟条件句往往都可以转化为if引导的条件句。常来表示含蓄虚拟条件的手段有：

（1）介词或介词短语，如but for, but that, without, in case of, under more favorable condition等。

Without the leadership of the party, we could not be living a happy today.=If there hadn't been the leadership of the party, we could not be living a happy today.

A. In spite of B. But for C. Because of D. As for 答案选B。

(2)连词，如：so that, unless, in case, supposing, lest, provided(倘若......)，for fear that(