虛擬語氣(Subjunctive Mood) 這壹語法項目也是考試中的重點之壹。虛擬語氣是壹種特殊的動詞形式，用來表示說話人所說的話並不是事實，而是壹種假設、願望、懷疑或推測。判斷是真實條件句還是非真實條件句。只有在非真實條件句中才使用虛擬語氣。通過句子意思，看假設的條件是否能夠實現，能夠實現是真實條件句，不能使用虛擬語氣；假設的條件不能實現則是非真實條件句，要用虛擬語氣，判斷這個假設是與哪個事實相反。通常有三種情況：①與過去事實相反 ②與現在事實相反 ③與將來事實可能相反。
I: 最基本的虛擬語氣句型:
1. 虛擬現在時表示與現在事實相反的假設，其if 從句的謂語形式用動詞的過去式(be 壹般用were)，主句用would/ should/ could/ might +動詞原形。If places were alike, there would be little need for geographers.如果各個地方都壹樣，就不需要地理學家了。
2. 虛擬過去時是表示與過去事實相反的假設，if 從句的謂語形式用過去完成時即had＋過去分詞，主句用would / should / could / might + have +過去分詞。If he had known your address yesterday,he would have telephoned you.
3. 虛擬將來時是表示對將來實現的可能性很小的或不確定的假設。If從句的謂語形式用壹般過去式或用were to / should +動詞原形，主句用would / should/could/ might +動詞原形。If he were to leave today, he would get there by Friday
4. 省略if 采用倒裝語序的條件句。有時可以把含有助動詞、情態動詞、be或have的虛擬條件句中的連詞if省去，而將had , should, were 等詞提到主語之前，即用倒裝結構。If he had worked harder, he would have got through the exams.==>Had he worked harder, he would have got through the exams.If he were to leave today, he would get there by Friday.==>Were he to leave today, he would get there by Friday.If I were in your place, I wouldn’t do that.==>Were I in your place, I wouldn’t do that.
5. 有時虛擬條件句並沒用if 從句表示出來，而是用介詞短語(otherwise, or, without, but for)、上下文或其它方式來表示。如：We didn't know his telephone number; otherwise we would have telephoned him. Without you help, I wouldn’t have achieved so much. But for （“要不是......”的意思）your help, I would not have succeeded.
II: 虛擬語氣在從句中用should的情況:
1. 在表示建議,要求,命令,想法的動詞後的從句裏, 用should + 動詞原形, should 可以省略. 如 advise, agree, command, decide, demand, determine, grant, indicate, insist, order, prefer, propose, request, require, stipulate, suggest, urge, vote.常考到的是: suggest, advise, demand, require, propose, insist, order, request.
His doctor suggested that he (should) take short leave of absence.
The author proposed that TV (should) be turned off at least one hour every day.
2. 在表示建議,要求,命令,想法的名詞後的從句裏, 用should + 動詞原形, should可以省略. 如 advice, decision,agreement, command, decree, demand, determination, indication, insistence, order, preference, proposal, request, requirement, stipulation etc.
It was Bill’s suggestion that everyone (should) have a map.
His suggestion was that everyone (should) have a map.
He gave us a suggestion that everyone (should) have a map.
3. 在It is/was +形容詞後的that 從句中用should的結構, should 可以省略. 這類形容詞常見的有: advisable, anxious, compulsory, crucial, desirable, eager, essential, fitting, imperative(絕對必要), impossible, improper, important, natural, necessary, obligatory, possible, preferable, probable, recommended, urgent, vital etc.
It‘s natural that she (should) do so.
It is essential that we (should) tell her the news.
4. 在 lest 和 for fear that(以免),in case(以防)從句中用should, should 可以省略.
She walked quietly lest she (should) wake up her roommates.
Have your gun ready in case we should need it.
III: wish 後的that 從句中:
1. 表示現在或將來的願望,從句中過去式.
I wish I knew his address.
I wish I were young.
2. 表示過去沒有實現或不可能實現的願望, 從句用過去完成式或would, could, might + have + 過去分詞.
I wish you had written to him.
I wish I could have slept longer this morning, but I had to get up and come to class.
3. 如果將wish改成wished, 其後that 從句中動詞的形式不變.
4. 如果that 從句中用would , 壹般表示 對現狀不滿或希望未來有所改變或請求
I wish he would answer my letter.
I wish prices would come down.
I wish you would help me.
I wish you would stop asking silly questions.
IV: 在 It’s about/ high/ first(second, third etc)time 後的that從句中,用過去式.表示“該是做什麽的時候了”
It is about time you were in bed.
It is high time we left.
It is the first time I came here.
V: 在would rather, would sooner, would just as soon 後的that從句中,用過去式或過去完成式,表示“寧願做什麽”
I would rather he came tomorrow than today.
John would rather that she had not gone to the party yesterday evening.
VI: 在if only（“如果....就好了”的意思） 感嘆句中，謂語動詞與wish賓語從句的虛擬形式相同。
If only he didn’t drive so fast!(現在)
If only she had asked someone’s advice.(過去)
If only the rain would stop.(將來)
VII: 在as if / as though 從句中，表示和現在事實相反或對現在情況有所懷疑用過去式；表示過去想象中的動作或情況，用過去完成式。
He speaks as if he were on the spot.
She spoke to me as if I were deaf.
This device operated as though it had been repaired.
註: 1. 在 as if / as though 句中, 如果有可能成為事實, 用陳述語氣.
He looks as if he is going to be ill.
2. 在insist 後的從句中, 如果是堅持自己, 用陳述語氣, 堅持別人做什麽事情, 用虛擬語氣.
She insists that she is right.
She insisted that I should finish the work at once.