虛擬語氣是一種動詞形式，表示說話人的一種願望，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。
If I were you, I'd take them away.
如果我是你的話，我就會帶走他們。
If I had met Li Hua, I could had told him.
如果我碰見了李華，我就告訴了他了。
If I had time. I could come to help you.
如果我有時間，我會來幫助你的。
He suggested that our class should be divided into five groups.
他建議說我們的班應該分成五個小組。
He speaks to us as if he had been there.
他給我們講的好象他去過那兒。
虛擬語氣的用法
1) 虛擬語氣用在簡單句中，表示祝願，命令。
May you be happy.
祝你幸福。
May you have a good time.
祝願你玩的痛快。
May the friendship between us last long.
祝願我們的友情天長地久。
Have a good journey!
祝願你旅途愉快!
You go out!
你出去!
2) 虛擬語氣用在賓語從句中。動詞 wish, suggest,order,insist, propose,等詞後面的賓語從句表示的是一種虛擬語氣， 賓語從句中的動詞動作表示的只是一種願望，要求。
I wish she would be on my side.
我希望她能站在我一邊。
I wish I could help him.
我希望我能幫助他。
He insisted that all of us should be there on time by any means.
他堅持要我們大家想盡辦法按時去那兒。
動詞 demand, suggest, order, insist, propose 後面的從句中，"should" 可以省略。
The teacher suggested that we (should) clean the blackboard after class.
老師建議我們課後把黑板擦了。
He ordered that the students wash the clothes every week by themselves.
他要求學生每周都要自己洗衣服。