結(jié)構(gòu)︰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(bào)價感興趣，請與我們聯(lián)系。

　　If I should ……， I will ……

　　結(jié)構(gòu)︰If…should…，…would（will）/should（shall）等+原形動詞

　　說明︰這是表示與未來事實(shí)相反的假設(shè)，if 要用 should，譯成“萬一”。should可置于前，將 if 省略。的則視可能性做變化：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(jì)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(jié)構(gòu)︰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(shè)，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。

　　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(dāng)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(jié)構(gòu)︰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(shí)相反的假設(shè)句型。if 中的，不論為第幾人稱，一律用 were，were 可置于主詞前面，而省略 if.過去式除用 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，它們與原形結(jié)合起來構(gòu)成。

　　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(fēng)了。

　　If I had binoculars， I could see that comet clearly.

　　如果我有望遠(yuǎn)鏡，我就可以清楚地看見那顆彗星。

　　It is time that ……

　　結(jié)構(gòu)︰It is（high）time+（that）+主詞+過去式動詞

　　說明︰此句型意為“已經(jīng)到了…的時間了”。過去式處有時亦使用“should+原形”。that 也能用 to 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(dāng)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(jīng)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(yīng)對進(jìn)退之禮儀的時候了。