虛擬語氣表示說話人的主觀願望、猜疑、建議或與事實不符的假設等，而不表示客觀存在的事實。虛擬語氣是由句中的謂語動詞的特殊形式表現出來的。快跟小北老師一起來學習一下吧~
一、虛擬語氣謂語動詞的幾種表現形式
1. 用在虛擬條件句中
虛擬條件句及其主句的謂語形式可歸納如下:
例1：I would certainly go if I had the time.
例2：How nice it would be if you could stay a bit longer.
例3：She would have come if we had invited her.
注：如果條件從句中包含有were, had, should或could，有時可把if省略掉，但這時要把were, had, should或could放在主語前面(這種結構在口語中較少使用)。
例如：
1)Had we made adequate preparations, we might have succeeded.
Had we made = If we had made
2)Were there no gravity, there would be no air around us.
3)Should it rain tomorrow, the meeting would be put off.
2. 用在含蓄條件句中
句子中，假設的情況不用條件從句表示出來，而是用一個介詞短語來表示，句子的謂語形式也可遵循上表的規則。
這種用法也常見於or, or else, otherwise和but後面的分句中。
例如：
1)Without music, the world would be a dull place.
2)But for your help, we would have failed.
3)She would have gone with us, but she didn’t have time.
4)He must have had an accident, or he would have been here then.
3.用在錯綜時間條件句中
有時候，條件從句表示的動作和主句表示的動作發生的時間並不一致，這時，謂語動詞的形式要根據表示的時間來調整，這種句子可稱作錯綜時間條件句。
例如：
1)If you hadn’t watched television so late, you wouldn’t be so sleepy now.
此句為時間交錯的虛擬條件句，從句表示與過去事實相反的假設，主句則假設與現在情況相反
2)If you were in better health, we would have allowed you to join them in the work.
從句表示與現在事實相反的假設，主句則表示一種與過去事實相反的設想.
4.用在wish後的賓語從句中
這種句子主要表示願望，that常省略。
若指現在或將來的願望，從句用過去時;若指過去沒有實現的願望，從句用過去完成時。
例如：
1)I wish I had learned to play chess.(與過去事實相反)
2)I wish I remembered his address.(與現在事實相反)
3)I wish he would try again.(對將來情況的假設)
若wish 後的賓語從句中用would，可以表示請求，通常意味著說話人的不快或不滿。
例如：
1)I wish you would help us.
2)I wish you would stop asking such silly questions.
5.用在if only感嘆句中
當表示“但願”，“要是…就好”時，它的用法和wish基本相同，只是更富有感情色彩，表示一時很難實現的願望。
例如：
1)If only I knew what you wanted.
2)If only you hadn’t told him what I said, everything would have been all right.
6.用在以as if (as though) 引出的方式狀語從句中
當表示過去想象中的動作或情況時，用過去完成時;當表示和現在事實相反或對現在情況有所懷疑時，用一般過去時。
例如：
1)The old couple loved the orphan girl as if she had been their daughter.
2)It seems as if it were spring.
7.用在某些虛擬的定語從句中
例1：He was the very person I should have been wished to see.
例2：It’s (high) time that we went to class.
8.用以表示說話人的主觀願望或選擇，僅用在一些慣用句型的從句中
例1：I’d rather they came tomorrow.
例2：He’d rather I went to Fuzhou by sea.
例3：I’d just as soon you didn’t watch television this evening.
但had rather, would rather, would just as soon, would sooner等慣用語如用在簡單句中，其後都用不加to的動詞不定式。
例如：
1)I’d rather die than give up my principle.
2)I’d just as soon (would sooner) resign than take part in such dishonest deals.
二、用固定的情態動詞表示的虛擬語氣
1. should +動詞原形(有時省略should)
(1)用在動詞如advise, command, demand, desire, insist, order, propose, recommend, request, require, suggest, urge等後的賓語從句中。
例如：
1)They requested that we (should) send a delegation to their country.
2)She urged that he write and accept the post.
(2)用在it is suggested, it is desired, it is required, it was ordered, it was proposed, it has been decided, it is necessary (essential, imperative, important, desirable) that等引出的主語從句中。
例如：
1)It is desired that we (should) get everything ready by tonight.
2)It is necessary that the teacher (should) have a thorough knowledge of the subject he teaches.
(3)用在suggestion, motion, proposal, order, recommendation, plan, idea, requirement等引起的表語從句和同位語從句.
例如：He put his coat over the child lest he should catch cold.
2.用在表示比擬的方式狀語從句中
例如：They talked as if they had been friends for years.
3.用在表示虛擬情況的定語從句中
例如：It is high time you handed in your test paper.
4.用在某些表示主觀願望的名詞從句中
例1：I wish I were as strong as you.
例2：He insisted that we (should) take up the matter at the meeting.
5.用在婉轉的請求、建議、批評等句子中
例1：Could you spare me a few minutes?
例2：You might have told me earlier.
例3：Hadn’t you better go and see you dentist about that tooth?
6.用在表示祝願的簡單句中
例1：Long live world peace.
例2：May you succeed.
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