虚拟语气作为英语学科的重点和难点，在专升本考试中是一个独立的语法考查题型，大家必须完全掌握这一考点。
从专升本考查的情况看，三种与事实相反的条件句和主句的基本结构，以及用其他形式代替条件句和虚拟条件句的倒装是考查的重点。
今天小普为大家整理出专升本英语中虚拟语气知识点，同学们结合真题食用更佳！
》》》用于条件句
一、用于 if 引导的非真实条件句
1. 与现在事实相反，从句用动词的过去式（be的过去式用were），主句用would/should/could/might＋动词原形。
2. 与过去事实相反，从句用had＋过去分词，would/should/could/might+have+过去分词。
3. 与将来事实相反，从句用动词的过去式(be的过去式用were;should/were to+动词原形，主句用would/should/could/might＋动词原形。
If I were a boy，I would join the army．
If my brother had taken my advice，he would have succeeded in the competition.If it were to rain tomorrow ，the football match would be put off．
注意：主句中的should通常用于第一人称，would／could可以用于各种人称。
Were I to do the work，I should do it some other day．
If I had his telephone number, I would call him now．
If he had worked hard, he would have been in New York now．
二、用于含蓄条件句
在表示假设的虚拟语气中，有时假设的条件并不以条件从句的形式出现，而是通过上下文或句中内在的逻辑关系，或用其他形式表达出来，这就是“含蓄条件句”。常用的有以下几种方式：
1. 介词或介词短语，如but for，without，in case of, under，with，in等。
But for their help，we could not get over the difficulties．
Without music，the world would be a dull place．
2. 连词，如or，otherwise，but，in case，lest，for fear that，so that等。
We took a taxi to the airport．Otherwise we should have been late．
He felt very tired yesterday，or he would have attended the party．
注意：由lest，for fear that和in case引起的从句中谓语动词多用“should+动词原形”，但也可以不用虚拟语气，而用动词的陈述语气形式。
3. 分词短语
United（等于If they had been united）, they wouldn’t have been defeated.
4. 动词不定式短语
To hear him speak English, one would think him an Englishman.
5. 名词短语和“名词＋ and”结构
A diligent student would have worked harder.One step further and you would be dead.
6. 定语从句
Anyone who had been in your position would have done the same.
7. 形容词及其比较级
A more careful person would not have made so many mistakes.
8. 独立主格结构或由 with 引导的复合结构
All things considered, the price would be reasonable.
三、用于混合条件句
条件从句表示的动作与主句表示的动作在时间上不一致的叫混合条件句 （错综时间条件句）。
其主句和从句的谓语动词应根据各自所指的时间选用适当的形式，一般从句指过去，主句指现在或将来；或从句不指某一特定时间，主句指过去；或从句用虚拟语气，主句用陈述语气或祈使语气。
If you had asked him yesterday, you would know what to do now.
If the weather had been more favourable, the crops would be growing better.
四、虚拟条件句的倒装
在虚拟条件句中，如果从句部分含有 were, should 或 had，可将 if 省略，were, should 或 had置于从句句首，使用倒装。
Were they here now, they could help us.
Should it rain, the crops would be saved.
Had you come earlier, you would have got the ticket.
