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。
2. 條件句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裏了。
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。
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等詞置於句首。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裏工作了
(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，來表示説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. 要是我現在在家裏該多好啊。
If only I had got it. 要是我得到它了該多好啊。
二、其他狀語從句的虛擬語氣
1. 目的狀語從句中的虛擬語氣
(1) 在 for fear that, in case, lest 引導的目的狀語從句中，若用虛擬語氣時，從句謂語為： should + 動詞原形。並且 should 不能省略
She examined the door again for fear that a thief should come in. 她又把門檢查了一遍，以防盜賊的進入。
He started out earlier lest he should be late. 他很早就出發了以防遲到。
(2) 在 so that, in order that 所引導的目的狀語從句中，從句中的謂語為：can / may / could / might / will / would / should + 動詞原形。如(from )：
He goes closer to the speaker so that he can hear him clearer. 他走近説話的人以便能挺得更清楚。
He read the letter carefully in order that he should not miss a word. 他把信讀得很仔細以便不漏掉一個單詞。
2. 讓步狀語從句中的虛擬語氣
(1) 在 even if, even though 所引導的讓步狀語從句中，可用虛擬語氣，主句、從句的結構與 if 所引導的條件從句結構相同。如：
Even if he were here himself, he should not know what to do. 即使他親自來也不知該怎麼辦。
Nobody could save him even though Hua Tuo should come here. 即使華佗在世也救不了他。
(2) 在whatever, whichever, whenever, whoever, wherever, however, no matter wh-word 等引導的讓步狀語從句中，從句虛擬語氣結構為：
① may +動詞原形(指現在或將來)。如：
We will finish it on time no matter what / whatever may happen. 不管發生什麼事，我們都要按時完成。
We will find him wherever / no matter where he may be. 無論他在哪裏，我們都要找到他。
I will wait for him no matter how late he may come. 不管他來的多麼晚，我都會等他。
② may +完成式(指過去) ，主句結構不限。如：
You mustn’t be proud whatever / no matter what great progress you may have made. 不管你取得了多麼大的進步，你也不能驕傲(from )。
We must respect him no matter what / whatever mistakes he may have made. 不管他翻過什麼錯誤，我們必須尊敬他。
(3) 在though, although等引導的讓步狀語從句中，從句虛擬語氣結構為 should +動詞原形，主句結構不限。如：
Although / Though he should often be late, he is a good student. 儘管他經常遲到，他還是個好學生。
Although / Though he should be secretary, he must obey the rules. 儘管他是書記，他也必須遵守規定。
3. 方式狀語從句中的虛擬語氣
as if, as though 引導的方式狀語從句常用虛擬語氣。虛擬語氣的結構為下圖所示。
例如：
They began to talk warmly as if they had known each other for long. 他們開始熱烈的談論起來就好像他們已相互認識很久了。
He coughed twice as if someone should come. 他咳嗽兩聲就好像有人要來了。
4. 原因狀語從句中的虛擬語氣
amazed, angry, annoyed, astonished, disappointed, frightened, happy, pleased, proud, sorry, surprised, upset 等後面的狀語從句中常用虛擬語氣。其虛擬語氣的結構為：
① should + 原形動詞(指現在或將來)。如：
He was angry that you should call him by name. 他很生氣，你竟然對他直呼其名。
I was astonished that he should not answer such an easy question. 我很驚訝他竟答不出如此簡單的問題。
② should + 完成式, 指過去。如：
I’m very sorry that you should have failed the exam. 我很遺憾，你這次考試竟然失敗了。
I was very surprised that Father should have known what I did yesterday. 我很吃驚，父親竟指導我昨天所作的事情
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