虛擬語氣是一種動詞形式,表示說話人的一種愿望,假設,懷疑,猜測, 建議等含義,虛擬語氣所表示的含義不是客觀存在的事實.它的用法在表情達意的過程中發(fā)揮著重要的作用.近幾年高考在單項選擇這一題型中出現(xiàn)不多,但在完形填空和短文改錯中仍然大量出現(xiàn).例如,2003年高考完形填空第38題考察的就是在篇章語境中的虛擬語氣在賓語從句中的用法.虛擬語氣的實際用法主要包括以下幾種：
1、 虛擬語氣用在簡單句中,表示“強烈的祝愿或命令的語氣”. 常用“May+主語+動詞原形”或“主語+動詞原形”.例如：May the friendship between us last long. 祝愿我們的友情天長地久. You go out! 你出去!
2、 虛擬語氣在賓語從句中的用法.由wish引導的賓語從句常表示說話人的一種強烈的卻暫時無法實現(xiàn)的愿望.
How I wish she would be on my side!(But in fact it’squite impossible.我多么希望她能站在我一邊啊!
How I wish I could help him! 我多么希望我能幫助他啊! How I wish I had watched the close NBA game last night.
另外,在表示“命令”、“堅持”、“要求”或“建議”等意義的及物動詞（order, command, demand, require, insist, suggest, propose, advise）之后的賓語從句中的謂語動詞同樣常使用虛擬語氣,表示說話人的要求,其結構為：主語+should+動詞原形,其中的should?？墒÷?例如：The head teacher demanded that we (should ) finish the task in time today.
但是,當insist表示“堅持認為”的意思時,或suggest表示“暗示”或“表明”之意時,賓語從句仍用陳述語氣.試比較：My parents insisted that I ( should) enter a key university. /My parents insisted that they were right.
The soldier’spale face suggested that he was happy to have given his life to his motherland.
The monitor suggested that we (should ) hold a class meeting tomorrow afternoon to discuss the problem.
3、 虛擬語氣用在主語從句中.
在句型 "It is important (necessary, strange, natural, a pity, suggested, advised, demanded, commanded, ordered ) that . " 中,that 后面的從句中的謂語動詞常用：“ should + 動詞原形 ”.例如：
It's necessary that we should have a walk now. 我們有必要出去散散步.
It's natural that she should do so.她這樣做是很自然的.
It's suggested that we should take good care of the patient.
同理,在表示“命令”、“堅持”、“要求”或“建議”等意義的名詞前后的主語從句、表語從句和同位語從句中的謂語動詞同樣用虛擬語氣,既：“主語+(should)+ 動詞原形”的句型.例如：
His suggestion /advice is that we should start early tomorrow morning.
3、虛擬語氣用在狀語從句中.
虛擬語氣最多地用在表示條件的狀語從句和表示結果的主句中.在表示與事實相反的虛擬語氣時,動詞有三種虛擬形式,即虛擬條件現(xiàn)在式,過去式和將來式.
1) 虛擬條件現(xiàn)在式：表示與現(xiàn)在事實相反的假設及根本不可能的假設或結果：
條件狀語從句
結果主句

If 主語+ 動詞過去式（be 用were）
主語+ would/could/should/might + 動詞原形

2)虛擬條件過去式：表示與過去事實相反的假設或結果：
條件狀語從句
結果主句

If+主語+ had + 過去分詞
主語+should/ would/could/might+ have+ 過去分詞.

3）虛擬條件將來式：表示與將來事實相反的假設或結果：
條件狀語從句
結果主句

If+ should /were to +動詞原形
主語+ should/ would/could/might+動詞原形

If I were you, I should get it. 如果我是你,我就買了它.
If I had time now, I would study French. 如果我現(xiàn)在有時間,我會學習法語的.
If you had got up earlier, you could have caught the train. 如果你早一點起床,就會趕上火車的.
If it were to be fine tomorrow, I would go shopping with my friends.
如果明天天氣好,我將和朋友們一起去買東西.