If + Present Tense ……， S + will/shall + V ……
結構︰If＋現(xiàn)在式…，S＋未來式…
說明︰if 子句用現(xiàn)在式，表示須具備的條件，主句用未來式表示可能的結果，整句含意為“如果…，那么…”。will 用于所有的人稱，在 I 和 we 之后可用 shall 代替 will.若主句的主詞為 I 或 we 時，可以用 shall 代替 will.像 if necessary（如果需要），if possible（如果可能），if so（如果這樣）等固定詞組實際上是省略了的 if 子句。
If I lose my job， I will/shall go abroad. 如果我失業(yè)了，我就出國。
If I have a headache， I will take an aspirin. 如果我頭痛，我就服一片阿斯匹林。
If it rains， we will stay at home. 如果下雨，我們將待在家里。
If the weather clears， we'll go for a walk. 如果天晴，我們就去散步。
If the weather doesn't clear， we won't go for a walk. 如果天不晴，我們就不去散步。
Inflation may be rising， if （it is） so， prices will go up.
通貨膨脹率可能上升。如果是這樣，物價就會上漲。
If possible， She wants to go with us. 可能的話，她想跟我們一起去。
Sterling may fall， if （this should be） so， interest rates will rise.
英國貨幣可能貶值，如果果真如此，利率就會上升。
If + Present Tense ……， S + Modal Verb ……
結構︰If + 現(xiàn)在式，主詞＋情態(tài)助動詞
說明︰本句型實為句型之變體。之所以用情態(tài)助動詞，主要是因為說話者對可能的結果不是太肯定或者是想表達例如必要的意思。
If it is fine tomorrow， we can go out. 如果明天天氣好，我門可以出門。
If it is fine tomorrow， we could go out. 如果明天天氣好，我門能夠出門。
If it is fine tomorrow， we may go out. 如果明天天氣好，我門可能出門。
If it is fine tomorrow， we might go out. 如果明天天氣好，我門可能出門。
If it is fine tomorrow， we should go out. 如果明天天氣好，我門宜于出門。
If it is fine tomorrow， we ought to go out. 如果明天天氣好，我門宜于出門。
If it is fine tomorrow， we must go out. 如果明天天氣好，我門必須出門。
If I should ……， Imperative Sentence.
結構︰If I＋should ……＋祈使語氣
說明︰代替，增加了條件的不確定性。本句型常用在想禮貌地提出要求或建議，或者想圓通地告訴他人該做什么事的場合。用 should 起始句子即可不用 if 而表示條件。這種用法比較正式，常用于諸如公函之中，而不用于日常會話。
If you should see him， please give him my regards. 如果你見到他，請代我向他致意。
Should you see him， please give him my regards. 如果你見到他，請代我向他致意。
If you should happen to see him， please give him my regards.
如果你萬一見到他，請代我向他致意。
Should you happen to see him， please give him my regards.
如果你萬一見到他，請代我向他致意。
If you should write to her， send her my love. 如果你給她寫信，請代我向她問候。
Should you not wish our agent to call， please let us know.
你若不希望我們的代理人去造訪，請告之。
Should you be interested in our offer， please contact us.
你若對我們的報價感興趣，請與我們聯(lián)系。
If I should ……， I will ……
結構︰If…should…，…would（will）／should（shall）等＋原形動詞
說明︰這是表示與未來事實相反的假設<句型>，if <子句>要用<助動詞> should，譯成“萬一”。should可置于<主詞>前，將 if 省略。<主要子句>的<助動詞>則視可能性做變化：若可能性低，則為過去式，若可能性高，則為現(xiàn)在式。should 可以提前，而將 if 省略。
If he should come， I would tell him the truth. 萬一他來，我會把真相告訴他。
If he should come， I will tell him the truth. 萬一他來，我一定會把真相告訴他。
Should the boy come again， I would throw him out. 要是那男孩在來，我就把他攆出去。
If it should rain， our plan would be spoiled. 萬一下雨，我們的計劃就泡湯了。
Should that be true， the contract would be canceled. 假如那是真的，合約就該取消。
Should another world war break out， what would become of human beings？
萬一另一次世界大戰(zhàn)爆發(fā)，人類將會發(fā)生什么事？
If I were to ……， I ……
結構︰If…were to…，…would／should 等＋原形動詞
說明︰這也是表示與未來狀況相反的假設<句型>，與“if …… should， ……”大致相同，但“if …… were to”所表示的可能性更低，通常用以表示“與真理相反”的<假設語氣>.
If the sun were to rise in the west， he would pass the exam.
要是太陽從西邊出來，他就會通過考試——他不可能通過考試。
If I were to be born again， I would like to be a bird. 我要是再活一次，我想當一只鳥。
If the sun were to disappear， what would the earth be like？
萬一太陽消失了，地球會變成什么樣子？
Were I to die tomorrow， what would my children do？
萬一明天我死了，我的孩子們將怎么辦呢？
If I + V-ed， I would ……
結構︰If…＋過去式動詞…，主詞＋過去式助動詞（would／should 等）＋原形動詞
說明︰這是與現(xiàn)在事實相反的假設句型。if <子句>中的<動詞>，不論<主詞>為第幾人稱，一律用 were，were 可置于主詞前面，而省略 if.過去式<助動詞>除用 should（用于第一人稱）、 would（用于第二、三人稱）外，還可用不分人稱的 could，might 和 ought to，它們與<動詞>原形結合起來構成<假設語氣>.
If I knew his address， I could write to him. 如果我知道他的住址，我會寫信給他。
If I were free now， I might call on him. 如果我有時間，我可能會去看他。
If you were in my shoes （=Were you in my shoes）， what would you do？
如果你站在我的立場，你會怎么做？
Were I rich enough， I would buy a sports car. 如果我有足夠的錢，我就買一輛賽車了。
How happy I would be if I were a few inches taller！ 要是我再高幾寸，我會好高興。
If I had a car， I could take her for a drive. 如果我有車， 我就帶她去兜風了。
If I had binoculars， I could see that comet clearly.
如果我有望遠鏡，我就可以清楚地看見那顆彗星。
It is time that ……
結構︰It is（high）time＋（that）＋主詞＋過去式動詞
說明︰此句型意為“已經到了…的時間了”。過去式<動詞>處有時亦使用“should＋<動詞>原形”。that <子句>也能用 to <不定詞>來表示。
It is time he went to bed. 該是他睡覺的時間了。
It is time that you left for the duty. 該你當班了。
It is time that you reflected upon your mistakes. 該是你反省思過的時候了。
It is high time he should come to our house for dinner.已經到了他該上咱家吃晚飯的時候了。
It is time for somebody to teach you to behave yourself.
該是有人教你應對進退之禮儀的時候了。
If I had V-ed， I would have ……
結構︰If…h(huán)ad＋過去分詞…，主詞＋would／should 等＋have＋過去分詞
說明︰這是與過去事實相反的假設<句型>.if <子句>要用<過去完成式>，<主要子句>則要用過去式<助動詞>（would，should，ought to，might，could）＋have＋過去<分詞>.if <子句>中的 had可置于<主詞>前面，而省略 If.
If I had seen him， I would have told him the truth. 如果我當時看見他，我會告訴他實情。
I could have finished the task if I had had more time.
如果當時我能有多一點時間，我就能完成這項任務。
If we had known of your departure， we would have seen you off at the airport.
如果我們事先知道你要離開，我們會到機場送行。
I someone had been with him， he might not have been drowned.
如果有人在他旁邊，或許他就不會溺死。
I might have been incredulous had I not been accustomed to such responses.
若非我已經習慣了這樣的回答，我可能不敢輕易相信。
Had he not apologize to her， she would not have forgiven him.
她（那時）不會原諒他，若非他道了歉。
Had he not saved me， I might have been drowned. 我可能溺死了，若非他救了我。
Had I proposed to you， would you have married me？
我要是當年向你求婚，你會答應嫁給我嗎？
Had you not helped us， we should have canceled this transaction.
假如沒有你的幫助，這筆生意早就告吹了。
If I had V-ed， I would ……
結構︰If…h(huán)ad＋過去分詞…，主詞＋would／should 等＋原形動詞＋now／today
說明︰這是<時態(tài)>不一致時的假設<句型>，亦稱混合假設條件句。即：if <子句>若與過去事實相反，用<過去完成式>表示；而<主要子句>若與現(xiàn)在事實相反，則用過去式<助動詞>表示。此類<主要子句>句尾通常有表現(xiàn)在的<時間副詞>，如 now，today 等。
If he had worked harder when young， he would be well off now.
如果他年輕時多努力一點，現(xiàn)在就能過得舒服些。
If I had been rich ten years ago， I could buy that house today.
如果十年前我有錢，今天我就能買下那棟房子了。
Had he told the truth， he wouldn't be punished now.如果他當時肯說實話，現(xiàn)在就不會受罪了。
Had he followed the doctor's advice， he might be alive now.
當時他要是聽了醫(yī)生的建議，現(xiàn)在可能還活著。
I wish …… + V-ed ……
結構︰I wish＋（that）＋主詞＋動詞過去式／過去完成式（had＋過去分詞）…
說明︰I wish 之后以 that <子句>為<受詞>時，該<子句>的<動詞>一定要用<假設語氣>：若<動詞>用過去式，表示與現(xiàn)在事實相反的愿望；若用<過去完成式>，則表示與過去事實相反的愿望。“I wish＋that-<子句>”的<句型>也可用“I would rather＋that-<子句>”取代。而 I hope 之后以 that <子句>做<受詞>時，該<子句>用一般<時態(tài)>.
I wish there were meadows and lambs. 但愿有草地與小羊。
I wish I were as tall as you. 但愿我像你一樣高。
I wish he could tell us. 但愿他能告訴我們。
I wish （=I would rather） he could come tomorrow. 但愿他明天能來。
I wish you had not been caught in the rain yesterday. 但愿昨天你們沒有淋到雨。
I wish you had not told the truth. 但愿你沒有說實話。
I wish I had known you ten years ago. 真希望十年前就已經認識你。
If only + V-ed
結構︰If only＋過去式／過去完成式
說明︰此句型意為“要是…就好了?！庇眠^去式，表示與現(xiàn)在事實相反；若用<過去完成式>，則表示與過去事實相反。
If only I had a rich father. 要是我有個有錢的爸爸就好了。
If only he had been here. 要是他當時在這兒就好了。
If only I had another chance. 要是我再有一次機會就好了。
…… as if/as though ……
結構︰…as if／as though…現(xiàn)在式／過去式／過去完成式
說明︰此句型意為“彷佛…；好像…一樣”。as if，as though 是<副詞><連接詞>，引導<副詞子句>.<子句>中，可用現(xiàn)在式，以表示事實；也可用過去式或<過去完成式>，分別表示與現(xiàn)在或過去事實相反的<假設語氣>.
He speaks like that as if he doesn't want to attend the meeting.他那樣說話，似乎不想參加會議。
He walks as if he is drunk. 他走起路來好像他真的醉了。
He felt as if he almost wished to kill them. 他感覺彷佛幾乎要殺掉他們。
The baby opened the book as if he were able to read. 這個嬰兒打開書本彷佛他會念書。
The nurse attends on the patient as if he were her father.
這護士照顧這位病人彷佛在照顧她爸爸似的。
He ran into the room as if he had seen something terrible.
他跑進屋子，彷佛他看到什么可怕的東西。
She looks as if nothing had happened to her. 她當時看起來好像什么事都沒發(fā)生似的。
It seems/looks as if ……
結構︰It seems／looks as if…
說明︰此句型意為“似乎…”。本句型中的 as if <子句>可用以表示事實，或<假設語氣>.
It looks as if it is going to rain. 好像要下雨了。
It seems as if he knows everything. 他似乎是個萬事通。
It seems as if he knew everything， but in reality， he is as stupid as can be.
他似乎是個萬事通。其實他是再愚蠢不過了。
It looks as if she had just come back from outer space.
她看起來彷佛剛從外層空間回來似的。
It seemed as if he had finished the work. 他似乎已經完成了這個工作。
It seemed as if he would never finish the work. 他似乎永遠完成不了這個工作。
If it were not for ……
結構︰if it were not for＋名詞／子句，主詞＋would／should 等＋原形動詞…
說明︰此句型意為“若非（有）…”。此類句構專門用于表示與現(xiàn)在事實相反的<假設語氣>.亦可用“but for＋<名詞>”或“without＋<名詞>”代替。were 可以提前，省略 if，如例句3.
If it were not for his presence， I would punish you. 要不是他在場，我會處罰你的。
But for your advice， I should have failed. 要不是你的忠告，我會失敗的。
But for music （=Were it not for music）， life would be dull. 要不是音樂，人生會很無聊。
If it were not for oxygen and nitrogen in the air， no man could live on the earth.
大氣中如果沒有氧和氮，人就無法生存于地球了。
Without air， all living things would die. 若非空氣，所有的生物都會死亡。
Without newspaper， we would get behind the times. 要不是報紙，我們都趕不上時代了。
I should be lonely， were it not for the birds and the flowers. 我會寂寞，若非有鳥也有花。
Were it not for his help， I could not finish the work.若非有他的幫助，我就不能完成這件工作。
Were it not for science， we could not live a comfortable live.
若非科學，我們無法過著舒適的生活。
If it had not been for ……
結構︰if it had not been for＋名詞／子句，主詞＋would／should 等＋原形動詞…
說明︰此句型意為“若非（有）…”。此類句構專門用于表示與過去事實相反的<假設語氣>.
If it had not been for his help， I should have failed. 如果沒有他的幫忙，我應該已經失敗。
Had it not been for your timely help， our company would have been on the verge of bankruptcy. 若非你及時伸出援助之手，本公司將會瀕臨破產的邊緣。
If it had not been for these experiments， the improvement of the machine would have been impossible. 要不是這些實驗，這部機器也許就不可能改良了。
Had it not been for the kind guide， I might have got lost in the mountains.
要不是這位好心的向導，我可能就在山中迷路了。
If it had not been that he was here， I would have punished you.
要不是他在場，我當時就會處罰你。
I demand/insist that ……
結構︰主詞1＋意志動詞（demand／insist 等）＋（that）＋主詞2＋（should）＋原形動詞
說明︰意志<動詞>有四類：建議（suggest，recommend，propose，advise，urge 等），要求（desire， ask，demand，require，request，maintain，insist 等），命令（order，command 等），規(guī)定（ rule，regulate，stipulate 等）。其后接 that-<子句>時，該<子句>里的<動詞>要用原形或“should＋<動詞>”。美式英語通常省略 should.
The committee moved that the meeting （should） be adjourned. 委員提議休會。
His parents demanded that he （should） be back by ten. 他的父母要求他十點以前回家。
The employees demand that their salaries be raised. 員工們要求加薪。
They ruled that the law （should） not be imposed. 他們規(guī)定不應加重法律。
His father ordered that he （should） keep a diary in English.
他的父親規(guī)定他要用英文寫日記。
My mother encouraged me and insisted that I continue my education.
我媽媽鼓勵我，而且堅持我應該繼續(xù)我的教育。
He insisted that I （should） apologize to her. 他堅持我應該向她道歉。
Recently， many states have insisted that high schools teach students how to drive.
最近，許多州堅持中學應該教學生如何開車。
His father insisted that they （should） move to the country. 他爸爸堅持他們應該搬到鄉(xiāng)下。
It is proper …… that ……
結構︰It is＋意志形容詞（important 等）＋（that）＋主詞＋（should）＋原形動詞
說明︰意志<形容詞>包括 important，necessary，imperative，essential，urgent，desirable， advisable，recommendable，proper 等。that-<子句>中只能用<助動詞> should，不可用 must，而 should 往往予以省略。
It is necessary that he （should） sort out the information for my reference.
他有必要整理些資料供我參考。
It is essential that he get up early. 他有必要早起。
It is urgent that food and clothing （should） be sent to the sufferers.
急需將食物和衣服送給災民。
It is desirable that we （should） provide for the poor at Christmas.
在圣誕節(jié)施舍窮人是可喜的事。
It is important that he be quiet. 他該保持安靜是有必要的。
It is important that he not do it. 他不該做那事是有必要的。
It is requested that all members be present at the party. 全體會員都被要求出席這次晚會。
It is proper that such a bad man be punished severely. 這么壞的人受重罰是應該的。
Imperative Sentence + Conj. + Main Clause
結構︰祈使句＋連接詞＋主句
說明︰<祈使句>表示須具備的條件，主句表示可能的結果。<祈使句>代替 if 子句進行評說，提出要求，訂立協(xié)議，提供建議或威脅等。<祈使句>的用法比 if 子句表示的更為緊迫。
Provide the materials and we'll do the job. 提供材料，我們就做這活。
Stop shouting or you'll wake up the neighbors. 不要喊了，否則你會把鄰居吵醒的。
Put that down or else I'll smack you. 把它放下，不然我就揍你。
Be there on time， otherwise you'll create a bad impression.
要準時來，否則你會給人一個壞的印象。
Fail to pay and they'll cut off the electricity. 你（如果）不付款，他們就要斷電。
Stop eating sweets， or you won't get any dinner. 你如果不停止吃糖，你就不要吃飯。
Unless ……
結構︰Unless＋子句，主要子句
說明︰此句型意為“除非…”。unless 引導一個否定假設句，相當于 if …… not ……，有時可以互換使用?？傮w上看，unless 的語氣強于 if …… not ……，而且有時較為常用，例如在最后通牒中。
Unless you change your mind （=If you don't change you mind）， I won't be able to help you.
除非你改變你的想法，否則我不能幫助你。
Unless the management improves their offer， there'll be a strike.
除非資方做出進一步的建議，否則將舉行罷工。
I couldn't have got to the meeting on time － unless I had caught an earlier train.
我不可能及時趕到會場，除非我趕上了較找的一班火車。
Provided/Providing （that） ……
結構︰Provided／provided（that）＋子句，S＋V ……
說明︰此句型意為“如果…”。Provided/Providing （that） 引導假設條件句，其功能相當于 if.
Provided/Providing （that） you clear your desk by this evening， you can have tomorrow off.
如果你到今晚把手頭上的工作做完，你明天就可以休息。
As/So long as ……
結構︰As/So long as ＋子句，S＋V ……
說明︰此句型意為“如果…，只要…”。As/So long as引導一個條件假設句，其功能相當于 if.
So （As） long as you clear your desk by this evening， you can have tomorrow leave.
如果你到今晚把手頭上的工作做完，你明天就可以休息。
As long as you drive carefully， you will be very safe. 如果你開車小心，你就會很安全。
You may eat anything， so long as you don't eat too much.
只要不吃得太多，你可以吃任何東西。
As long as live， I will help you. 只要我活著，我都會幫助你。
As long as you don't betray me， I'll do whatever you ask me to （do）。
只要你不出賣我，要我做什么我都愿意。
We'll ship the goods at an early time as long as there is a steamer.只要有船，我們就盡早裝貨。
You will never be good students so long as you goof around.
如果你們成天游手好閑，就永遠也成不了好學生。
Suppose/Supposing （that） ……
結構︰Suppose/Supposing （that）＋子句，S＋V ……
說明︰此句型意為“如果…，假使…”。Suppose/Supposing （that） 引導假設條件句，其功能相當于 if.
Suppose/Supposing （that） we miss the train， what shall we do？
如果我們誤了火車，我們將怎么辦？
What if/Say ……
結構︰What if/Say＋子句，S＋V ……
說明︰此句型意為“假設…”。What if 和 Say 用來引導一個假設條件句，其義相當于 Let us suppose（讓我們假設）。
What if/Say he goes home before us and can't get in？ What will he do then？
假設他在我們之前趕到家而又進不去呢？那他怎么辦呢？
What if/Say you were to run out of money？ What would you do？
假設你的錢用完了呢？你將怎么辦呢？
With luck ……
結構︰With luck，＋主要子句
說明︰With luck 為含蓄假設條件句（即不用 if 直接引導）。with luck 意為“如果幸運的話，如果運氣好的話”。
With luck， we'll be there by tomorrow.幸運的話，我們明天將到達那兒。（=If we are lucky）
With luck， she will get the job. 如果幸運的話，她將得到那份工作。（=If she is lucky）
Given time ……
結構︰Given time，＋主要子句
說明︰此為含蓄假設條件句（即不用 if 直接引導）。Given time 意為“（如果）給以時間的話”。
Given time， they will probably agree.給以時間的話，他們可能會同意。（=If they are given time/If we give them time）
To hear him talk， ……
結構︰To hear him talk，＋主要子句
說明︰此句型意為“聽某人談話（的口氣）…”。從形式上看，To hear him talk 似為不定式詞組，但實則為含蓄條件句（即不用 if 直接引導）。To hear him talk 相當于 If you could hear him talk.
To hear him talk， you'd think he was Prime Minister.
聽他談話（那口氣），你會以為他是首相呢。
To hear you talk， I'd think you were Prime Minister.
聽你談話（那口氣），我還以為你是首相呢。
結構︰If＋現(xiàn)在式…，S＋未來式…
說明︰if 子句用現(xiàn)在式，表示須具備的條件，主句用未來式表示可能的結果，整句含意為“如果…，那么…”。will 用于所有的人稱，在 I 和 we 之后可用 shall 代替 will.若主句的主詞為 I 或 we 時，可以用 shall 代替 will.像 if necessary（如果需要），if possible（如果可能），if so（如果這樣）等固定詞組實際上是省略了的 if 子句。
If I lose my job， I will/shall go abroad. 如果我失業(yè)了，我就出國。
If I have a headache， I will take an aspirin. 如果我頭痛，我就服一片阿斯匹林。
If it rains， we will stay at home. 如果下雨，我們將待在家里。
If the weather clears， we'll go for a walk. 如果天晴，我們就去散步。
If the weather doesn't clear， we won't go for a walk. 如果天不晴，我們就不去散步。
Inflation may be rising， if （it is） so， prices will go up.
通貨膨脹率可能上升。如果是這樣，物價就會上漲。
If possible， She wants to go with us. 可能的話，她想跟我們一起去。
Sterling may fall， if （this should be） so， interest rates will rise.
英國貨幣可能貶值，如果果真如此，利率就會上升。
If + Present Tense ……， S + Modal Verb ……
結構︰If + 現(xiàn)在式，主詞＋情態(tài)助動詞
說明︰本句型實為
If it is fine tomorrow， we can go out. 如果明天天氣好，我門可以出門。
If it is fine tomorrow， we could go out. 如果明天天氣好，我門能夠出門。
If it is fine tomorrow， we may go out. 如果明天天氣好，我門可能出門。
If it is fine tomorrow， we might go out. 如果明天天氣好，我門可能出門。
If it is fine tomorrow， we should go out. 如果明天天氣好，我門宜于出門。
If it is fine tomorrow， we ought to go out. 如果明天天氣好，我門宜于出門。
If it is fine tomorrow， we must go out. 如果明天天氣好，我門必須出門。
If I should ……， Imperative Sentence.
結構︰If I＋should ……＋祈使語氣
說明︰
If you should see him， please give him my regards. 如果你見到他，請代我向他致意。
Should you see him， please give him my regards. 如果你見到他，請代我向他致意。
If you should happen to see him， please give him my regards.
如果你萬一見到他，請代我向他致意。
Should you happen to see him， please give him my regards.
如果你萬一見到他，請代我向他致意。
If you should write to her， send her my love. 如果你給她寫信，請代我向她問候。
Should you not wish our agent to call， please let us know.
你若不希望我們的代理人去造訪，請告之。
Should you be interested in our offer， please contact us.
你若對我們的報價感興趣，請與我們聯(lián)系。
If I should ……， I will ……
結構︰If…should…，…would（will）／should（shall）等＋原形動詞
說明︰這是表示與未來事實相反的假設<句型>，if <子句>要用<助動詞> should，譯成“萬一”。should可置于<主詞>前，將 if 省略。<主要子句>的<助動詞>則視可能性做變化：若可能性低，則為過去式，若可能性高，則為現(xiàn)在式。should 可以提前，而將 if 省略。
If he should come， I would tell him the truth. 萬一他來，我會把真相告訴他。
If he should come， I will tell him the truth. 萬一他來，我一定會把真相告訴他。
Should the boy come again， I would throw him out. 要是那男孩在來，我就把他攆出去。
If it should rain， our plan would be spoiled. 萬一下雨，我們的計劃就泡湯了。
Should that be true， the contract would be canceled. 假如那是真的，合約就該取消。
Should another world war break out， what would become of human beings？
萬一另一次世界大戰(zhàn)爆發(fā)，人類將會發(fā)生什么事？
If I were to ……， I ……
結構︰If…were to…，…would／should 等＋原形動詞
說明︰這也是表示與未來狀況相反的假設<句型>，與“if …… should， ……”大致相同，但“if …… were to”所表示的可能性更低，通常用以表示“與真理相反”的<假設語氣>.
If the sun were to rise in the west， he would pass the exam.
要是太陽從西邊出來，他就會通過考試——他不可能通過考試。
If I were to be born again， I would like to be a bird. 我要是再活一次，我想當一只鳥。
If the sun were to disappear， what would the earth be like？
萬一太陽消失了，地球會變成什么樣子？
Were I to die tomorrow， what would my children do？
萬一明天我死了，我的孩子們將怎么辦呢？
If I + V-ed， I would ……
結構︰If…＋過去式動詞…，主詞＋過去式助動詞（would／should 等）＋原形動詞
說明︰這是與現(xiàn)在事實相反的假設句型。if <子句>中的
If I knew his address， I could write to him. 如果我知道他的住址，我會寫信給他。
If I were free now， I might call on him. 如果我有時間，我可能會去看他。
If you were in my shoes （=Were you in my shoes）， what would you do？
如果你站在我的立場，你會怎么做？
Were I rich enough， I would buy a sports car. 如果我有足夠的錢，我就買一輛賽車了。
How happy I would be if I were a few inches taller！ 要是我再高幾寸，我會好高興。
If I had a car， I could take her for a drive. 如果我有車， 我就帶她去兜風了。
If I had binoculars， I could see that comet clearly.
如果我有望遠鏡，我就可以清楚地看見那顆彗星。
It is time that ……
結構︰It is（high）time＋（that）＋主詞＋過去式動詞
說明︰此句型意為“已經到了…的時間了”。過去式<動詞>處有時亦使用“should＋<動詞>原形”。that <子句>也能用 to <不定詞>來表示。
It is time he went to bed. 該是他睡覺的時間了。
It is time that you left for the duty. 該你當班了。
It is time that you reflected upon your mistakes. 該是你反省思過的時候了。
It is high time he should come to our house for dinner.已經到了他該上咱家吃晚飯的時候了。
It is time for somebody to teach you to behave yourself.
該是有人教你應對進退之禮儀的時候了。
If I had V-ed， I would have ……
結構︰If…h(huán)ad＋過去分詞…，主詞＋would／should 等＋have＋過去分詞
說明︰這是與過去事實相反的假設<句型>.if <子句>要用<過去完成式>，<主要子句>則要用過去式<助動詞>（would，should，ought to，might，could）＋have＋過去<分詞>.if <子句>中的 had可置于<主詞>前面，而省略 If.
If I had seen him， I would have told him the truth. 如果我當時看見他，我會告訴他實情。
I could have finished the task if I had had more time.
如果當時我能有多一點時間，我就能完成這項任務。
If we had known of your departure， we would have seen you off at the airport.
如果我們事先知道你要離開，我們會到機場送行。
I someone had been with him， he might not have been drowned.
如果有人在他旁邊，或許他就不會溺死。
I might have been incredulous had I not been accustomed to such responses.
若非我已經習慣了這樣的回答，我可能不敢輕易相信。
Had he not apologize to her， she would not have forgiven him.
她（那時）不會原諒他，若非他道了歉。
Had he not saved me， I might have been drowned. 我可能溺死了，若非他救了我。
Had I proposed to you， would you have married me？
我要是當年向你求婚，你會答應嫁給我嗎？
Had you not helped us， we should have canceled this transaction.
假如沒有你的幫助，這筆生意早就告吹了。
If I had V-ed， I would ……
結構︰If…h(huán)ad＋過去分詞…，主詞＋would／should 等＋原形動詞＋now／today
說明︰這是<時態(tài)>不一致時的假設<句型>，亦稱混合假設條件句。即：if <子句>若與過去事實相反，用<過去完成式>表示；而<主要子句>若與現(xiàn)在事實相反，則用過去式<助動詞>表示。此類<主要子句>句尾通常有表現(xiàn)在的<時間副詞>，如 now，today 等。
If he had worked harder when young， he would be well off now.
如果他年輕時多努力一點，現(xiàn)在就能過得舒服些。
If I had been rich ten years ago， I could buy that house today.
如果十年前我有錢，今天我就能買下那棟房子了。
Had he told the truth， he wouldn't be punished now.如果他當時肯說實話，現(xiàn)在就不會受罪了。
Had he followed the doctor's advice， he might be alive now.
當時他要是聽了醫(yī)生的建議，現(xiàn)在可能還活著。
I wish …… + V-ed ……
結構︰I wish＋（that）＋主詞＋動詞過去式／過去完成式（had＋過去分詞）…
說明︰I wish 之后以 that <子句>為<受詞>時，該<子句>的<動詞>一定要用<假設語氣>：若<動詞>用過去式，表示與現(xiàn)在事實相反的愿望；若用<過去完成式>，則表示與過去事實相反的愿望。“I wish＋that-<子句>”的<句型>也可用“I would rather＋that-<子句>”取代。而 I hope 之后以 that <子句>做<受詞>時，該<子句>用一般<時態(tài)>.
I wish there were meadows and lambs. 但愿有草地與小羊。
I wish I were as tall as you. 但愿我像你一樣高。
I wish he could tell us. 但愿他能告訴我們。
I wish （=I would rather） he could come tomorrow. 但愿他明天能來。
I wish you had not been caught in the rain yesterday. 但愿昨天你們沒有淋到雨。
I wish you had not told the truth. 但愿你沒有說實話。
I wish I had known you ten years ago. 真希望十年前就已經認識你。
If only + V-ed
結構︰If only＋過去式／過去完成式
說明︰此句型意為“要是…就好了?！庇眠^去式，表示與現(xiàn)在事實相反；若用<過去完成式>，則表示與過去事實相反。
If only I had a rich father. 要是我有個有錢的爸爸就好了。
If only he had been here. 要是他當時在這兒就好了。
If only I had another chance. 要是我再有一次機會就好了。
…… as if/as though ……
結構︰…as if／as though…現(xiàn)在式／過去式／過去完成式
說明︰此句型意為“彷佛…；好像…一樣”。as if，as though 是<副詞><連接詞>，引導<副詞子句>.<子句>中，可用現(xiàn)在式，以表示事實；也可用過去式或<過去完成式>，分別表示與現(xiàn)在或過去事實相反的<假設語氣>.
He speaks like that as if he doesn't want to attend the meeting.他那樣說話，似乎不想參加會議。
He walks as if he is drunk. 他走起路來好像他真的醉了。
He felt as if he almost wished to kill them. 他感覺彷佛幾乎要殺掉他們。
The baby opened the book as if he were able to read. 這個嬰兒打開書本彷佛他會念書。
The nurse attends on the patient as if he were her father.
這護士照顧這位病人彷佛在照顧她爸爸似的。
He ran into the room as if he had seen something terrible.
他跑進屋子，彷佛他看到什么可怕的東西。
She looks as if nothing had happened to her. 她當時看起來好像什么事都沒發(fā)生似的。
It seems/looks as if ……
結構︰It seems／looks as if…
說明︰此句型意為“似乎…”。本句型中的 as if <子句>可用以表示事實，或<假設語氣>.
It looks as if it is going to rain. 好像要下雨了。
It seems as if he knows everything. 他似乎是個萬事通。
It seems as if he knew everything， but in reality， he is as stupid as can be.
他似乎是個萬事通。其實他是再愚蠢不過了。
It looks as if she had just come back from outer space.
她看起來彷佛剛從外層空間回來似的。
It seemed as if he had finished the work. 他似乎已經完成了這個工作。
It seemed as if he would never finish the work. 他似乎永遠完成不了這個工作。
If it were not for ……
結構︰if it were not for＋名詞／子句，主詞＋would／should 等＋原形動詞…
說明︰此句型意為“若非（有）…”。此類句構專門用于表示與現(xiàn)在事實相反的<假設語氣>.亦可用“but for＋<名詞>”或“without＋<名詞>”代替。were 可以提前，省略 if，如例句3.
If it were not for his presence， I would punish you. 要不是他在場，我會處罰你的。
But for your advice， I should have failed. 要不是你的忠告，我會失敗的。
But for music （=Were it not for music）， life would be dull. 要不是音樂，人生會很無聊。
If it were not for oxygen and nitrogen in the air， no man could live on the earth.
大氣中如果沒有氧和氮，人就無法生存于地球了。
Without air， all living things would die. 若非空氣，所有的生物都會死亡。
Without newspaper， we would get behind the times. 要不是報紙，我們都趕不上時代了。
I should be lonely， were it not for the birds and the flowers. 我會寂寞，若非有鳥也有花。
Were it not for his help， I could not finish the work.若非有他的幫助，我就不能完成這件工作。
Were it not for science， we could not live a comfortable live.
若非科學，我們無法過著舒適的生活。
If it had not been for ……
結構︰if it had not been for＋名詞／子句，主詞＋would／should 等＋原形動詞…
說明︰此句型意為“若非（有）…”。此類句構專門用于表示與過去事實相反的<假設語氣>.
If it had not been for his help， I should have failed. 如果沒有他的幫忙，我應該已經失敗。
Had it not been for your timely help， our company would have been on the verge of bankruptcy. 若非你及時伸出援助之手，本公司將會瀕臨破產的邊緣。
If it had not been for these experiments， the improvement of the machine would have been impossible. 要不是這些實驗，這部機器也許就不可能改良了。
Had it not been for the kind guide， I might have got lost in the mountains.
要不是這位好心的向導，我可能就在山中迷路了。
If it had not been that he was here， I would have punished you.
要不是他在場，我當時就會處罰你。
I demand/insist that ……
結構︰主詞1＋意志動詞（demand／insist 等）＋（that）＋主詞2＋（should）＋原形動詞
說明︰意志<動詞>有四類：建議（suggest，recommend，propose，advise，urge 等），要求（desire， ask，demand，require，request，maintain，insist 等），命令（order，command 等），規(guī)定（ rule，regulate，stipulate 等）。其后接 that-<子句>時，該<子句>里的<動詞>要用原形或“should＋<動詞>”。美式英語通常省略 should.
The committee moved that the meeting （should） be adjourned. 委員提議休會。
His parents demanded that he （should） be back by ten. 他的父母要求他十點以前回家。
The employees demand that their salaries be raised. 員工們要求加薪。
They ruled that the law （should） not be imposed. 他們規(guī)定不應加重法律。
His father ordered that he （should） keep a diary in English.
他的父親規(guī)定他要用英文寫日記。
My mother encouraged me and insisted that I continue my education.
我媽媽鼓勵我，而且堅持我應該繼續(xù)我的教育。
He insisted that I （should） apologize to her. 他堅持我應該向她道歉。
Recently， many states have insisted that high schools teach students how to drive.
最近，許多州堅持中學應該教學生如何開車。
His father insisted that they （should） move to the country. 他爸爸堅持他們應該搬到鄉(xiāng)下。
It is proper …… that ……
結構︰It is＋意志形容詞（important 等）＋（that）＋主詞＋（should）＋原形動詞
說明︰意志<形容詞>包括 important，necessary，imperative，essential，urgent，desirable， advisable，recommendable，proper 等。that-<子句>中只能用<助動詞> should，不可用 must，而 should 往往予以省略。
It is necessary that he （should） sort out the information for my reference.
他有必要整理些資料供我參考。
It is essential that he get up early. 他有必要早起。
It is urgent that food and clothing （should） be sent to the sufferers.
急需將食物和衣服送給災民。
It is desirable that we （should） provide for the poor at Christmas.
在圣誕節(jié)施舍窮人是可喜的事。
It is important that he be quiet. 他該保持安靜是有必要的。
It is important that he not do it. 他不該做那事是有必要的。
It is requested that all members be present at the party. 全體會員都被要求出席這次晚會。
It is proper that such a bad man be punished severely. 這么壞的人受重罰是應該的。
Imperative Sentence + Conj. + Main Clause
結構︰祈使句＋連接詞＋主句
說明︰<祈使句>表示須具備的條件，主句表示可能的結果。<祈使句>代替 if 子句進行評說，提出要求，訂立協(xié)議，提供建議或威脅等。<祈使句>的用法比 if 子句表示的更為緊迫。
Provide the materials and we'll do the job. 提供材料，我們就做這活。
Stop shouting or you'll wake up the neighbors. 不要喊了，否則你會把鄰居吵醒的。
Put that down or else I'll smack you. 把它放下，不然我就揍你。
Be there on time， otherwise you'll create a bad impression.
要準時來，否則你會給人一個壞的印象。
Fail to pay and they'll cut off the electricity. 你（如果）不付款，他們就要斷電。
Stop eating sweets， or you won't get any dinner. 你如果不停止吃糖，你就不要吃飯。
Unless ……
結構︰Unless＋子句，主要子句
說明︰此句型意為“除非…”。unless 引導一個否定假設句，相當于 if …… not ……，有時可以互換使用?？傮w上看，unless 的語氣強于 if …… not ……，而且有時較為常用，例如在最后通牒中。
Unless you change your mind （=If you don't change you mind）， I won't be able to help you.
除非你改變你的想法，否則我不能幫助你。
Unless the management improves their offer， there'll be a strike.
除非資方做出進一步的建議，否則將舉行罷工。
I couldn't have got to the meeting on time － unless I had caught an earlier train.
我不可能及時趕到會場，除非我趕上了較找的一班火車。
Provided/Providing （that） ……
結構︰Provided／provided（that）＋子句，S＋V ……
說明︰此句型意為“如果…”。Provided/Providing （that） 引導假設條件句，其功能相當于 if.
Provided/Providing （that） you clear your desk by this evening， you can have tomorrow off.
如果你到今晚把手頭上的工作做完，你明天就可以休息。
As/So long as ……
結構︰As/So long as ＋子句，S＋V ……
說明︰此句型意為“如果…，只要…”。As/So long as引導一個條件假設句，其功能相當于 if.
So （As） long as you clear your desk by this evening， you can have tomorrow leave.
如果你到今晚把手頭上的工作做完，你明天就可以休息。
As long as you drive carefully， you will be very safe. 如果你開車小心，你就會很安全。
You may eat anything， so long as you don't eat too much.
只要不吃得太多，你可以吃任何東西。
As long as live， I will help you. 只要我活著，我都會幫助你。
As long as you don't betray me， I'll do whatever you ask me to （do）。
只要你不出賣我，要我做什么我都愿意。
We'll ship the goods at an early time as long as there is a steamer.只要有船，我們就盡早裝貨。
You will never be good students so long as you goof around.
如果你們成天游手好閑，就永遠也成不了好學生。
Suppose/Supposing （that） ……
結構︰Suppose/Supposing （that）＋子句，S＋V ……
說明︰此句型意為“如果…，假使…”。Suppose/Supposing （that） 引導假設條件句，其功能相當于 if.
Suppose/Supposing （that） we miss the train， what shall we do？
如果我們誤了火車，我們將怎么辦？
What if/Say ……
結構︰What if/Say＋子句，S＋V ……
說明︰此句型意為“假設…”。What if 和 Say 用來引導一個假設條件句，其義相當于 Let us suppose（讓我們假設）。
What if/Say he goes home before us and can't get in？ What will he do then？
假設他在我們之前趕到家而又進不去呢？那他怎么辦呢？
What if/Say you were to run out of money？ What would you do？
假設你的錢用完了呢？你將怎么辦呢？
With luck ……
結構︰With luck，＋主要子句
說明︰With luck 為含蓄假設條件句（即不用 if 直接引導）。with luck 意為“如果幸運的話，如果運氣好的話”。
With luck， we'll be there by tomorrow.幸運的話，我們明天將到達那兒。（=If we are lucky）
With luck， she will get the job. 如果幸運的話，她將得到那份工作。（=If she is lucky）
Given time ……
結構︰Given time，＋主要子句
說明︰此為含蓄假設條件句（即不用 if 直接引導）。Given time 意為“（如果）給以時間的話”。
Given time， they will probably agree.給以時間的話，他們可能會同意。（=If they are given time/If we give them time）
To hear him talk， ……
結構︰To hear him talk，＋主要子句
說明︰此句型意為“聽某人談話（的口氣）…”。從形式上看，To hear him talk 似為不定式詞組，但實則為含蓄條件句（即不用 if 直接引導）。To hear him talk 相當于 If you could hear him talk.
To hear him talk， you'd think he was Prime Minister.
聽他談話（那口氣），你會以為他是首相呢。
To hear you talk， I'd think you were Prime Minister.
聽你談話（那口氣），我還以為你是首相呢。