1.条件句中的虚拟语气类型
(1)将来时的条件句中的虚拟语气。如:
If it were to rain tomorrow, the meeting would be put off.
(2)现在时的条件句中的虚拟语气。如:
If he studied at this school, he would know you well.
(3)过去时的条件句中的虚拟语气。如:
I could have done better if I had been more careful.

2.运用条件句中的虚拟语气时,须注意的几个问题
(1)当从句的主语为第三人称单数时,谓语动词若是系动词be时,可用was代替were。但在倒装虚拟结构及if I were you, as it were中,只能用were。如:Were I ten years younger, I would study abroad.

(2)当条件状语从句表示的行为和主句表示的行为所发生的时间不一致时,动词的形式要依据它所表示的时间来调整。
①从句的动作与过去事实相反,而主句的动作与现在或现在正在发生的事实不符。如:
If I had worked hard at school, I would be a teacher, too.
If they had informed us, we would not come here now.
②从句的动作与现在事实相反,而主句的动作与过去事实不符。如:
If he were free today, we would have sent him to Beijing.
③从句的动作与过去发生的情况相反,而主句的动作与现在正在发生的情况相反。如:
If it had not been raining too much, the crops would be growing much better.

(3)当虚拟条件句的谓语动词含有were, should, had时,if可省略,而将were, should, had等词置于句首。如:
Should he agree to go there, we would send him there.
Were she here, she would agree with us.
Had he learnt about computers, we would have hired him to work here.

(4)有时,句子没有直接给出假设情况的条件,而须通过上下文或其他方式来判断。如:
I would have come to see you, but I was too busy.
But for his help, we would be working now.
Without your instruction, I would not have made such great progress.

(5)有时,虚拟条件句中,主、从句可以省略其中的一个,来表示说话人的一种强烈的感情。
①省略从句
He would have finished it.
You could have passed this exam.
②省略主句
If I were at home now.
If only I had got it.