If + Present Tense ， S + will/shall + V

结构︰If+现在式，S+未来式

说明︰if 子句用现在式，表示须具备的条件，主句用未来式表示可能的结果，整句含意为如果，那么。will 用于所有的人称，在 I 和 we 之后可用 shall 代替 will.若主句的主词为 I 或 we 时，可以用 shall 代替 will.像 if necessary(如果需要)，if possible(如果可能)，if so(如果这样)等固定词组实际上是省略了的 if 子句。

If I lose my job， I will/shall go abroad. 如果我失业了，我就出国。

If I have a headache， I will take an aspirin. 如果我头痛，我就服一片阿斯匹林。

If it rains， we will stay at home. 如果下雨，我们将待在家里。

If the weather clears， well go for a walk. 如果天晴，我们就去散步。

If the weather doesnt clear， we wont go for a walk. 如果天不晴，我们就不去散步。

Inflation may be rising， if (it is) so， prices will go up.

通货膨胀率可能上升。如果是这样，物价就会上涨。

If possible， She wants to go with us. 可能的话，她想跟我们一起去。

Sterling may fall， if (this should be) so， interest rates will rise.

英国货币可能贬值，如果果真如此，利率就会上升。

If + Present Tense ， S + Modal Verb

结构︰If + 现在式，主词+情态助动词

说明︰本句型实为句型之变体。之所以用情态助动词，主要是因为说话者对可能的结果不是太肯定或者是想表达例如必要的意思。

If it is fine tomorrow， we can go out. 如果明天天气好，我门可以出门。

If it is fine tomorrow， we could go out. 如果明天天气好，我门能够出门。

If it is fine tomorrow， we may go out. 如果明天天气好，我门可能出门。

If it is fine tomorrow， we might go out. 如果明天天气好，我门可能出门。

If it is fine tomorrow， we should go out. 如果明天天气好，我门宜于出门。

If it is fine tomorrow， we ought to go out. 如果明天天气好，我门宜于出门。

If it is fine tomorrow， we must go out. 如果明天天气好，我门必须出门。

If I should ， Imperative Sentence.

结构︰If I+should +祈使语气

说明︰代替，增加了条件的不确定性。本句型常用在想礼貌地提出要求或建议，或者想圆通地告诉他人该做什么事的场合。用 should 起始句子即可不用 if 而表示条件。这种用法比较正式，常用于诸如公函之中，而不用于日常会话。

If you should see him， please give him my regards. 如果你见到他，请代我向他致意。

Should you see him， please give him my regards. 如果你见到他，请代我向他致意。

If you should happen to see him， please give him my regards.

如果你万一见到他，请代我向他致意。

Should you happen to see him， please give him my regards.

如果你万一见到他，请代我向他致意。

If you should write to her， send her my love. 如果你给她写信，请代我向她问候。

Should you not wish our agent to call， please let us know.

你若不希望我们的代理人去造访，请告之。

Should you be interested in our offer， please contact us.

你若对我们的报价感兴趣，请与我们联系。

If I should ， I will

结构︰Ifshould，would(will)/should(shall)等+原形动词

说明︰这是表示与未来事实相反的假设句型，if 子句要用助动词 should，译成万一。should可置于主词前，将 if 省略。主要子句助动词则视可能性做变化：若可能性低，则为过去式，若可能性高，则为现在式。should 可以提前，而将 if 省略。

If he should come， I would tell him the truth. 万一他来，我会把真相告诉他。

If he should come， I will tell him the truth. 万一他来，我一定会把真相告诉他。

Should the boy come again， I would throw him out. 要是那男孩在来，我就把他撵出去。

If it should rain， our plan would be spoiled. 万一下雨，我们的计划就泡汤了。

Should that be true， the contract would be canceled. 假如那是真的，合约就该取消。

Should another world war break out， what would become of human beings?

万一另一次世界大战爆发，人类将会发生什么事?

If I were to ， I

结构︰Ifwere to，would/should 等+原形动词

说明︰这也是表示与未来状况相反的假设句型，与if should， 大致相同，但if were to所表示的可能性更低，通常用以表示与真理相反的假设语气.

If the sun were to rise in the west， he would pass the exam.

要是太阳从西边出来，他就会通过考试他不可能通过考试。

If I were to be born again， I would like to be a bird. 我要是再活一次，我想当一只鸟。

If the sun were to disappear， what would the earth be like?

万一太阳消失了，地球会变成什么样子?

Were I to die tomorrow， what would my children do?

万一明天我死了，我的孩子们将怎么办呢?

If I + V-ed， I would

结构︰If+过去式动词，主词+过去式助动词(would/should 等)+原形动词

说明︰这是与现在事实相反的假设句型。if 子句中的 动词，不论主词为第几人称，一律用 were，were 可置于主词前面，而省略 if.过去式助动词除用 should(用于第一人称)、 would(用于第二、三人称)外，还可用不分人称的 could，might 和 ought to，它们与动词原形结合起来构成假设语气.

If I knew his address， I could write to him. 如果我知道他的住址，我会写信给他。

If I were free now， I might call on him. 如果我有时间，我可能会去看他。

If you were in my shoes (=Were you in my shoes)， what would you do?

如果你站在我的立场，你会怎么做?

Were I rich enough， I would buy a sports car. 如果我有足够的钱，我就买一辆赛车了。

How happy I would be if I were a few inches taller! 要是我再高几寸，我会好高兴。

If I had a car， I could take her for a drive. 如果我有车， 我就带她去兜风了。

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

如果我有望远镜，我就可以清楚地看见那颗彗星。

It is time that

结构︰It is(high)time+(that)+主词+过去式动词

说明︰此句型意为已经到了的时间了。过去式动词处有时亦使用should+动词原形。that 子句也能用 to 不定词来表示。

It is time he went to bed. 该是他睡觉的时间了。

It is time that you left for the duty. 该你当班了。

It is time that you reflected upon your mistakes. 该是你反省思过的时候了。

It is high time he should come to our house for dinner.已经到了他该上咱家吃晚饭的时候了。

It is time for somebody to teach you to behave yourself.

该是有人教你应对进退之礼仪的时候了。

If I had V-ed， I would have

结构︰Ifhad+过去分词，主词+would/should 等+have+过去分词

说明︰这是与过去事实相反的假设句型子句要用过去完成式主要子句则要用过去式助动词 (would，should，ought to，might，could)+have+过去分词子句中的 had可置于主词前面，而省略 If.

If I had seen him， I would have told him the truth. 如果我当时看见他，我会告诉他实情。

I could have finished the task if I had had more time.

如果当时我能有多一点时间，我就能完成这项任务。

If we had known of your departure， we would have seen you off at the airport.

如果我们事先知道你要离开，我们会到机场送行。

I someone had been with him， he might not have been drowned.

如果有人在他旁边，或许他就不会溺死。

I might have been incredulous had I not been accustomed to such responses.

若非我已经习惯了这样的回答，我可能不敢轻易相信。

Had he not apologize to her， she would not have forgiven him.

她(那时)不会原谅他，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?

我要是当年向你求婚，你会答应嫁给我吗?

Had you not helped us， we should have canceled this transaction.

假如没有你的帮助，这笔生意早就告吹了。

If I had V-ed， I would

结构︰Ifhad+过去分词，主词+would/should 等+原形动词+now/today

说明︰这是时态不一致时的假设句型，亦称混合假设条件句。即：if 子句若与过去事实相反，用过去完成式而主要子句若与现在事实相反，则用过去式助动词表示。此类主要子句句尾通常有表现在的时间副词，如 now，today 等。

If he had worked harder when young， he would be well off now.

如果他年轻时多努力一点，现在就能过得舒服些。

If I had been rich ten years ago， I could buy that house today.

如果十年前我有钱，今天我就能买下那栋房子了。

Had he told the truth， he wouldnt be punished now.如果他当时肯说实话，现在就不会受罪了。

Had he followed the doctors advice， he might be alive now.

当时他要是听了医生的建议，现在可能还活着。

I wish + V-ed

结构︰I wish+(that)+主词+动词过去式/过去完成式(had+过去分词)

说明︰I wish 之后以 that 子句受词时，该子句动词一定要用假设语气：若动词用过去式，表示与现在事实相反的愿望;若用过去完成式，则表示与过去事实相反的愿望。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 子句受词时，该子句用一般时态.

I wish there were meadows and lambs. 但愿有草地与小羊。

I wish I were as tall as you. 但愿我像你一样高。

I wish he could tell us. 但愿他能告诉我们。

I wish (=I would rather) he could come tomorrow. 但愿他明天能来。

I wish you had not been caught in the rain yesterday. 但愿昨天你们没有淋到雨。

I wish you had not told the truth. 但愿你没有说实话。

I wish I had known you ten years ago. 真希望十年前就已经认识你。

If only + V-ed

结构︰If only+过去式/过去完成式

说明︰此句型意为要是就好了。用过去式，表示与现在事实相反;若用过去完成式，则表示与过去事实相反。

If only I had a rich father. 要是我有个有钱的爸爸就好了。

If only he had been here. 要是他当时在这儿就好了。

If only I had another chance. 要是我再有一次机会就好了。

as if/as though

结构︰as if/as though现在式/过去式/过去完成式

说明︰此句型意为彷佛好像一样。as if，as though 是副词连接词，引导副词子句子句中，可用现在式，以表示事实;也可用过去式或过去完成式，分别表示与现在或过去事实相反的假设语气.

He speaks like that as if he doesnt want to attend the meeting.他那样说话，似乎不想参加会议。

He walks as if he is drunk. 他走起路来好像他真的醉了。

He felt as if he almost wished to kill them. 他感觉彷佛几乎要杀掉他们。

The baby opened the book as if he were able to read. 这个婴儿打开书本彷佛他会念书。

The nurse attends on the patient as if he were her father.

这护士照顾这位病人彷佛在照顾她爸爸似的。

He ran into the room as if he had seen something terrible.

他跑进屋子，彷佛他看到什么可怕的东西。

She looks as if nothing had happened to her. 她当时看起来好像什么事都没发生似的。

It seems/looks as if

结构︰It seems/looks as if

说明︰此句型意为似乎。本句型中的 as if 子句可用以表示事实，或假设语气.

It looks as if it is going to rain. 好像要下雨了。

It seems as if he knows everything. 他似乎是个万事通。

It seems as if he knew everything， but in reality， he is as stupid as can be.

他似乎是个万事通。其实他是再愚蠢不过了。

It looks as if she had just come back from outer space.

她看起来彷佛刚从外层空间回来似的。

It seemed as if he had finished the work. 他似乎已经完成了这个工作。

It seemed as if he would never finish the work. 他似乎永远完成不了这个工作。

If it were not for

结构︰if it were not for+名词/子句，主词+would/should 等+原形动词

说明︰此句型意为若非(有)。此类句构专门用于表示与现在事实相反的假设语气.亦可用but for+名词或without+名词代替。were 可以提前，省略 if，如例句3.

If it were not for his presence， I would punish you. 要不是他在场，我会处罚你的。

But for your advice， I should have failed. 要不是你的忠告，我会失败的。

But for music (=Were it not for music)， life would be dull. 要不是音乐，人生会很无聊。

If it were not for oxygen and nitrogen in the air， no man could live on the earth.

大气中如果没有氧和氮，人就无法生存于地球了。

Without air， all living things would die. 若非空气，所有的生物都会死亡。

Without newspaper， we would get behind the times. 要不是报纸，我们都赶不上时代了。

I should be lonely， were it not for the birds and the flowers. 我会寂寞，若非有鸟也有花。

Were it not for his help， I could not finish the work.若非有他的帮助，我就不能完成这件工作。

Were it not for science， we could not live a comfortable live.

若非科学，我们无法过着舒适的生活。

If it had not been for

结构︰if it had not been for+名词/子句，主词+would/should 等+原形动词