1.條件句中的虛擬語氣類型
(1)將來時的條件句中的虛擬語氣。如：
If it were to rain tomorrow, the meeting would be put off.
(2)現(xiàn)在時的條件句中的虛擬語氣。如：
If he studied at this school, he would know you well.
(3)過去時的條件句中的虛擬語氣。如：
I could have done better if I had been more careful．

2.運用條件句中的虛擬語氣時，須注意的幾個問題
(1)當從句的主語為第三人稱單數(shù)時，謂語動詞若是系動詞be時，可用was代替were。但在倒裝虛擬結(jié)構(gòu)及if I were you, as it were中，只能用were。如：Were I ten years younger, I would study abroad.

(2)當條件狀語從句表示的行為和主句表示的行為所發(fā)生的時間不一致時，動詞的形式要依據(jù)它所表示的時間來調(diào)整。
①從句的動作與過去事實相反，而主句的動作與現(xiàn)在或現(xiàn)在正在發(fā)生的事實不符。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從句的動作與現(xiàn)在事實相反，而主句的動作與過去事實不符。如：
If he were free today, we would have sent him to Beijing.
③從句的動作與過去發(fā)生的情況相反，而主句的動作與現(xiàn)在正在發(fā)生的情況相反。如：
If it had not been raining too much, the crops would be growing much better.

(3)當虛擬條件句的謂語動詞含有were, should, had時，if可省略，而將were, should, had等詞置于句首。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)有時，句子沒有直接給出假設(shè)情況的條件，而須通過上下文或其他方式來判斷。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)有時，虛擬條件句中，主、從句可以省略其中的一個，來表示說話人的一種強烈的感情。
①省略從句
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.