虛擬語氣用法詳解：
一、條件句中的虛擬語氣
1. 條件句中虛擬語氣的形式
從句中提出一種與客觀現實不相符或根本不可能存在的條件，主句會產生的一種不可能獲得的結果。條件句中的虛擬語氣根據不同的時間有三種不同的形式。
時間 從句謂語形式 主句謂語形式
將來 動詞過去式(be用were)
should + 動詞原形
were to + 動詞原形
would / should / might / could + 動詞原形
現在 動詞過去式(be 用 were) would / should / might / could + 動詞原形
過去 had +動詞過去分詞 would / should / might / could have + 動詞過去分詞
2. 條件中的虛擬語氣的舉例
(1) 將來時的條件句中的虛擬語氣。如：
If he should go to Qing Hua University, he would make full use of his time. 如果他要上清華大學的話，他就會充分利用他的時間了。
If he were to come here, he would tell us about it. 如果他要來的話，他會通知我們一聲。
(2) 現在時的條件句中的虛擬語氣。如：
If he were free, he would help us. 要是他有空的話，它會幫助我們的。
If he studied at this school, he would know you well. 如果他在這所學校學習的話，它會對你很熟悉。
(3) 過去時的條件句中的虛擬語氣。如：
If I had seen the film, I would have told you about it. 我如果看過這場電影，我會把電影內容告訴你了。
If I had got there earlier, I would have met Mr. Li. 如果我早點到那兒，我就會會到了李先生。
3. 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。但在倒裝虛擬結構及if I were you, as it were中，只能用were。如：
Were I ten years younger, I would study abroad. 要是我還年輕十歲的話，我會去國外學習。
If I were you, I would try my best to grasp the chance. 要是我是你的話，我要盡力抓住這次機會。
(2) 有時，虛擬條件句中，主、從句的動作若不是同時發生時，須區別對待。
①從句的動作與過去事實相反，而主句的動作與現在或現在正在發生的事實不符。如：
If I had worked hard at school, I would be an engineer, too. 如果我在學校學習刻苦的話，我現在也會使工程師了
If they had informed us, we would not come here now. 如果他們通知過我們的話，我們現在就不會來這里了。
②從句的動作與現在事實相反，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. 如果他今天有空的話，我們會已經派他去北京了(from http://www.enmajor.com/)。
If he knew her, he would have greeted her. 要是他認識她的話，他肯定會去問候她了。
③從句的動作與過去發生的情況相反，而主句的動作與現在正在發生的情況相反。如：
If it had not been raining too much, the crops would be growing much better. 如果天不下太多的雨的話，莊家會長得更好。
If he had been working hard, he would be working in the office now. 要是他工作一直努力的話，他現在已進了辦公室了。
(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. 要是他答應去的話，我們就派他去。
Were she here, she would agree with us. 如果她在這兒的話，她會同意我們的。
Had he learnt about computers, we would have hired him to work here. 如果她懂一些電腦知識的話，我們會已經聘用他來這里工作了(from http://www.enmajor.com/)。
(4) 有時，句子沒有直接給出假設情況的條件，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. 我本該來看你了，然而我太忙了。
But for his help, we would be working now. 要不是他的幫助，我們還會在工作呢。
Without your instruction, I would not have made such great progress. 要是沒有你的指導，我不會取得如此大的進步。
(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. 他本該完成了。
You could have passed this exam. 你應該會通過這次考試了。
②省略主句
If I were at home now. 要是我現在在家里該多好啊。
If only I had got it. 要是我得到它了該多好啊。
