英語中虛擬語氣的用法很多。在英語教學的過程中，我們常常發(fā)現(xiàn)有些學生對各種虛擬語氣結構中的動詞是用現(xiàn)在虛擬式還是過去虛擬式分辨不清，下面我就這個問題作一一說明。
1．表示有可能實現(xiàn)的意愿的虛擬結構中，動詞常用現(xiàn)在虛擬式：
（1）It is + adj + that +Sb + do/be + Sth
該結構中的主語從句表示說話人的意愿或主觀態(tài)度，結構中的形容詞用來表現(xiàn)說者的意愿趨向, 從句中的動詞應用現(xiàn)在虛擬式?？捎糜谠摻Y構中的形容詞包括 advisable, appropriate, crucial, desirable, essential, fitting, imperative（必要的）, important, impossible, natural, necessary, obligatory（必須）, preferable（更好的）, proper, sad, strange, surprising, vital（至關重要的）等。
如：It is necessary that the car be checked thoroughly.
It was important that she have confidence in herself.
（2） S1 + v + that S2 + do Sth
在帶有賓語從句的英語句子中，如主句中的謂語動詞表示以下有可能實現(xiàn)的意愿時，從句中的動詞應用現(xiàn)在虛擬式：
<1> 要求: ask, beg, demand, insist, request, require,
<2> 建議: advise, advocate, propose, recommend, suggest
<3> 命令: command, direct（命令, decree（裁決）instruct, move, order, urge, stipulate。
<4> 愿望: desire, expect, prefer（寧愿）。
<5> 決定：decide?！?BR> 如：He insisted that you be on time.
It is desired that we get everything ready by tonight.
The commanding officer decided that no one be admitted without a special pass.
（3）N+(…) that +sb +do sth
表示要求、建議、命令、愿望、決定等意義的名詞后如有其同位語從句或表語從句時，這類從句中的動詞應用現(xiàn)在虛擬式。適用于該句型的名詞有advice, conviction, decision, decree, demand, idea, motion, necessity, order, plan, preference, proposal, recommendation, requirement, resolution (決議), suggestion, wish。
如：My idea is that we go right now.
The resolution that women be allowed to vote was carried.
（4）Fear/be afraid/worried lest Sb do Sth 表示害怕(擔心)某種可能出現(xiàn)的情況，從句中的動詞應用現(xiàn)在虛擬式。
如: I fear lest he arrive too late.
We were afraid lest it be stolen.
He was at once worried lest she leave him.
2．在用來表示不太可能實現(xiàn)的意愿或假設的虛擬結構中，動詞常用過去虛擬式：
（1）Would that sb did sth/ had done sth
該結構表示與現(xiàn)實相反的愿望（would充當及物動詞），that從句中的動詞應用過去虛擬式。
如：Would that I were a student again.
Would that you didn't refuse my proposal of marriage（求婚）.
Would that I had told him the change last Friday.
（2）If only
If only有兩種主要用法:
① 表示目前較難實現(xiàn)的愿望或與過去事實相反的愿望。表示目前較難實現(xiàn)的愿望時使
If only Sb+ did/were Sth 或 if only Sb could/would do/be Sth的結構；表示與過去事實相反的愿望時使用if only Sb had done/been Sth 或 if only Sb could have done Sth的結構。
如：Oh, if he could only come
If only you would listen to reason.
If only I could have gone to the movies.
If only you hadn't told Linda what I said.
② if only 還可帶一個條件狀語從句，該條件句表示一種較難兌現(xiàn)的條件。
如：If only you would help me type my paper this afternoon, I would not have to burn the midnight oil.
If only they were here now, we would be able to discuss the issue together.
（3）But for和Except for（若非）
but for 和except for均需置于句首，其后均可接名詞短語，表示與事實相反的假設或條件，其后句子中的謂語要用should/would/could (not)do/be…來表示對現(xiàn)在的虛擬；而用should/would (not) have done/been… 來表示對過去的虛擬。
如：But/Except for air and water, nothing could live in the earth.
But/Except for the storm, I could have swam across the Channel.
But/Except for Martin's arms, I would have collapsed.
(4) but that（若非）
But that 后接真實情況的條件從句，該從句不用虛擬式，可置于句首或句中，而主句則需用 虛擬式Sb would (not) have done Sth（對過去）。
如：But that he was prevented, he would have shot the other gay.
He would have said no but that he was afraid.
（5）If引導的非真實條件句
在If 引導的非真實條件句中，if Sb did/were sth表示對現(xiàn)在或將來的虛擬，這時主句用would do sth/would be doing sth來表示現(xiàn)在或將來難以實現(xiàn)的愿望或假設；if Sb had done/been sth表示對過去的虛擬，這時主句用could/might/should/would have done/been sth來表示過去未能實現(xiàn)的愿望或假設。如果省去條件句中的if，則引起該條件句的倒裝。
如：If I were you, I'd marry her.
If we were men, we'd be doing something decent now.
Had he come earlier, he would have met her.
I should have talked to mother if I had thought of it.
（6）if it were not / had not been for…
該結構也是由if引導的非真實條件句，其中if it were not for…是與現(xiàn)在事實相反的條件句（句中的were不可替換成was），意為"要不是…"，這時主句中的動詞使用過去將來式；if it had not been for…是與過去事實相反的條件句，這時主句中的動詞使用過去將來完成式（另外，該條件句中的if如被省去時則引起倒裝）。
例如：If it had not been for the newspaper, I would never have found my lost daughter.
Were it not for the sun, there would be no plant on our planet.
（7）Sb wish后的賓語從句
Sb wish后的賓語從句要用虛擬語氣，表示與實際情況相反的愿望，其中對過去的虛擬要用Sb wish that Sb/sth had done或could/ might/would have done sth；對現(xiàn)在的虛擬要用Sb wish that Sb/sth were/did sth；對將來的虛擬要用Sb wish that Sb/sth could/might/would do sth。
如：I wish I had bought the house.
I wish you could have passed the test.
He wishes he were my age.
We wish you would try again.
（8）As if/though + Sb (or sth did/were 或 as if/though + Sb (or sth) had done/been
該結構表示非真實的想法或比喻, 結構中的動詞用過去虛擬式。
如:You look as if you'd seen a ghost.
Why is she looking at me as though she knew me? I've never seen her before in my life.
（9）It is (high/about) time that sb + did/were Sth.
該結構表示"到了非要做某事的時候了（早該做某事了），現(xiàn)在已錯過了做某事的時機了"從句中的動詞要用過去虛擬式。
如：It's about time you wrote your homework.
It is high time that you went to bed.
注意：該結構從句中的動詞如果是be動詞的話，接在第一、三人稱單數(shù)的主語之后時應該用was而不用were，
如：It is high time that I was in bed.
1．表示有可能實現(xiàn)的意愿的虛擬結構中，動詞常用現(xiàn)在虛擬式：
（1）It is + adj + that +Sb + do/be + Sth
該結構中的主語從句表示說話人的意愿或主觀態(tài)度，結構中的形容詞用來表現(xiàn)說者的意愿趨向, 從句中的動詞應用現(xiàn)在虛擬式?？捎糜谠摻Y構中的形容詞包括 advisable, appropriate, crucial, desirable, essential, fitting, imperative（必要的）, important, impossible, natural, necessary, obligatory（必須）, preferable（更好的）, proper, sad, strange, surprising, vital（至關重要的）等。
如：It is necessary that the car be checked thoroughly.
It was important that she have confidence in herself.
（2） S1 + v + that S2 + do Sth
在帶有賓語從句的英語句子中，如主句中的謂語動詞表示以下有可能實現(xiàn)的意愿時，從句中的動詞應用現(xiàn)在虛擬式：
<1> 要求: ask, beg, demand, insist, request, require,
<2> 建議: advise, advocate, propose, recommend, suggest
<3> 命令: command, direct（命令, decree（裁決）instruct, move, order, urge, stipulate。
<4> 愿望: desire, expect, prefer（寧愿）。
<5> 決定：decide?！?BR> 如：He insisted that you be on time.
It is desired that we get everything ready by tonight.
The commanding officer decided that no one be admitted without a special pass.
（3）N+(…) that +sb +do sth
表示要求、建議、命令、愿望、決定等意義的名詞后如有其同位語從句或表語從句時，這類從句中的動詞應用現(xiàn)在虛擬式。適用于該句型的名詞有advice, conviction, decision, decree, demand, idea, motion, necessity, order, plan, preference, proposal, recommendation, requirement, resolution (決議), suggestion, wish。
如：My idea is that we go right now.
The resolution that women be allowed to vote was carried.
（4）Fear/be afraid/worried lest Sb do Sth 表示害怕(擔心)某種可能出現(xiàn)的情況，從句中的動詞應用現(xiàn)在虛擬式。
如: I fear lest he arrive too late.
We were afraid lest it be stolen.
He was at once worried lest she leave him.
2．在用來表示不太可能實現(xiàn)的意愿或假設的虛擬結構中，動詞常用過去虛擬式：
（1）Would that sb did sth/ had done sth
該結構表示與現(xiàn)實相反的愿望（would充當及物動詞），that從句中的動詞應用過去虛擬式。
如：Would that I were a student again.
Would that you didn't refuse my proposal of marriage（求婚）.
Would that I had told him the change last Friday.
（2）If only
If only有兩種主要用法:
① 表示目前較難實現(xiàn)的愿望或與過去事實相反的愿望。表示目前較難實現(xiàn)的愿望時使
If only Sb+ did/were Sth 或 if only Sb could/would do/be Sth的結構；表示與過去事實相反的愿望時使用if only Sb had done/been Sth 或 if only Sb could have done Sth的結構。
如：Oh, if he could only come
If only you would listen to reason.
If only I could have gone to the movies.
If only you hadn't told Linda what I said.
② if only 還可帶一個條件狀語從句，該條件句表示一種較難兌現(xiàn)的條件。
如：If only you would help me type my paper this afternoon, I would not have to burn the midnight oil.
If only they were here now, we would be able to discuss the issue together.
（3）But for和Except for（若非）
but for 和except for均需置于句首，其后均可接名詞短語，表示與事實相反的假設或條件，其后句子中的謂語要用should/would/could (not)do/be…來表示對現(xiàn)在的虛擬；而用should/would (not) have done/been… 來表示對過去的虛擬。
如：But/Except for air and water, nothing could live in the earth.
But/Except for the storm, I could have swam across the Channel.
But/Except for Martin's arms, I would have collapsed.
(4) but that（若非）
But that 后接真實情況的條件從句，該從句不用虛擬式，可置于句首或句中，而主句則需用 虛擬式Sb would (not) have done Sth（對過去）。
如：But that he was prevented, he would have shot the other gay.
He would have said no but that he was afraid.
（5）If引導的非真實條件句
在If 引導的非真實條件句中，if Sb did/were sth表示對現(xiàn)在或將來的虛擬，這時主句用would do sth/would be doing sth來表示現(xiàn)在或將來難以實現(xiàn)的愿望或假設；if Sb had done/been sth表示對過去的虛擬，這時主句用could/might/should/would have done/been sth來表示過去未能實現(xiàn)的愿望或假設。如果省去條件句中的if，則引起該條件句的倒裝。
如：If I were you, I'd marry her.
If we were men, we'd be doing something decent now.
Had he come earlier, he would have met her.
I should have talked to mother if I had thought of it.
（6）if it were not / had not been for…
該結構也是由if引導的非真實條件句，其中if it were not for…是與現(xiàn)在事實相反的條件句（句中的were不可替換成was），意為"要不是…"，這時主句中的動詞使用過去將來式；if it had not been for…是與過去事實相反的條件句，這時主句中的動詞使用過去將來完成式（另外，該條件句中的if如被省去時則引起倒裝）。
例如：If it had not been for the newspaper, I would never have found my lost daughter.
Were it not for the sun, there would be no plant on our planet.
（7）Sb wish后的賓語從句
Sb wish后的賓語從句要用虛擬語氣，表示與實際情況相反的愿望，其中對過去的虛擬要用Sb wish that Sb/sth had done或could/ might/would have done sth；對現(xiàn)在的虛擬要用Sb wish that Sb/sth were/did sth；對將來的虛擬要用Sb wish that Sb/sth could/might/would do sth。
如：I wish I had bought the house.
I wish you could have passed the test.
He wishes he were my age.
We wish you would try again.
（8）As if/though + Sb (or sth did/were 或 as if/though + Sb (or sth) had done/been
該結構表示非真實的想法或比喻, 結構中的動詞用過去虛擬式。
如:You look as if you'd seen a ghost.
Why is she looking at me as though she knew me? I've never seen her before in my life.
（9）It is (high/about) time that sb + did/were Sth.
該結構表示"到了非要做某事的時候了（早該做某事了），現(xiàn)在已錯過了做某事的時機了"從句中的動詞要用過去虛擬式。
如：It's about time you wrote your homework.
It is high time that you went to bed.
注意：該結構從句中的動詞如果是be動詞的話，接在第一、三人稱單數(shù)的主語之后時應該用was而不用were，
如：It is high time that I was in bed.