支if的英语

连接词 conj. 1.(表示条件)如果He will come if you invite him. 如果你请他,他会来的。 2.(表示虚拟)假如,要是If I were you, I would never do that. 如果我是你,我决不做那件事。 3.(表示让步)即使We'll go even if it rains. 即使下雨我们也要去。 4.是否I wonder if she is ill. 不知她是否病了。 5.(表示因果关系)每一次...的时候(总是会)If I feel any doubt, I inquire. 我一感到有疑问就随时询问。 if作为连词的时候，一般用于条件状语从句或者是宾语从句或让步状语从句if引导的条件状语从句：If he comes, please tell me.（如果，假如）主句和从句位置可以互换，时态：主将从现变成：Please tell me,if he comes.宾语从句中：I want to know if（是否） he comes.可改成：I want to know whether he comes.当句子中有or not是 只能用whether——I want to know whether he comes or not.时态：1.主过从过 2.主句一般现在时，从句任何时 3.客观真理用一般现在时让步状语从句中，if 解释为即使名词 cn. 条件;设想There are too many ifs in his offer. 他的提议中条件太多了

if作为从属连词,可引导条件状语从句、让步状语从句和名词从句。if引导条件状语从句,从句可为真实条件从句,也可为虚拟条件从句。如为真实条件从句,谓语用陈述语气,表示可能性很大,作“假使”“如果”解,通常用一般现在时代替一般将来时; 如果if从句中用will,表示意愿。从句如为虚拟条件从句,谓语动词要用虚拟语气,表示可能性不大或与过去事实相反,作“要是,假如”解。可指过去的情况,也可指现在和将来的情况。指将来情况时可用were to或should。在现代口语中,一、三人称后常用was代替were。if引导的虚拟条件句中,助动词were,should,had可以移至主语前,此时if可省略。if引导的条件从句中可以省略be和主语。if引导的条件从句,有时后接only以加强其语气,表示说话人非常盼望某人提出的条件能够实现。if可引导让步状语从句,作“虽然,即使”解,常和even连用。if可引导名词性从句,作“是否”解,常放在ask, doubt, know, learn, see, wonder等动词后。一般用在口语中,而且不能用于句首。if可以表示惊奇或愤怒。用于陈述语气的否定句时,意义则是肯定的。If ever...在现代英语中,表示强调,用于加强主句的意思,往往含有否定意思。When or if〔when, or if〕表示从句所说的也许不会实现。if any的意思是“如果有的话”。if only可表示对现时或未来的愿望,也可表示与过去事实相反的愿望,作“只要…但愿,要是…就好了”解。What will happen if...?意思是“要是…怎么办”。常缩略成What if...?If not后可加动词,通常动词省略,可用于现在时态或现在完成时态,表示“要不,不然”; 也可用于yes〔no〕疑问句之后,表示“许诺,告诫”。If you demand his presence,warn him in advance.如果你要他来,就事先通知他。If you will be so kind as to help us, we can finish by six.如果你愿意帮助我们,到六点时咱们就能完成了。If you were a bird,you could fly.如果你是鸟,你就能飞行了。I should have talked to mother if I had thought of it.如果当初我想到了,我就和妈妈说了。If I were to ask him for a loan,would he agree ?如果我向他借钱的话,他能同意吗?If it should rain tomorrow,the rally would be postponed.要是明天下雨,群众大会就会延期举行。If I were an architect,I'd redesign this house.如果我是建筑师,我会重新设计这房子。If it were up there, it would be easier to find.如果它在那儿,就会更容易被找到。If had anything happened, he would have let me know.如果当初发生了什么事,他会让我知道的。If necessary, give me a ring.如果需要,给我打个电话。He will come, if invited.如果受到邀请,他会来的。If only somebody had told us, we could have warned you.如果有人告诉了我们,我们就能事先提醒你。We will go even if it rains.即使下雨,我们也要去。If he is poor, at least he is honest.他虽然穷,但至少是诚实的。I don't know if he was there.我不知道他当初是否在那里。

1.(表示条件)如果 ,主句用将来时,if从句用现在时表示将来He will come if you invite him.如果你请他,他会来的.2.(表示虚拟)假如,要是 1）时态：可以表示过去,现在和将来的情况.它的基本特点是时态退后.a.同现在事实相反的假设.句型 ：条件从句 主句 一般过去时 should( would) +动词原形If they were here,they would help you.b.表示于过去事实相反的假设.句型：条件从句 主句 过去完成时 should(would) have+ 过去分词If she had worked harder,she would have succeeded.The rice would not have been burnt if you had been more careful.If my lawyer had been here last Saturday,he would have prevented me from going.If he had come yesterday,I should / would have told him about it.含义：He did not come yesterday,so I did not tell him about it.If he had not been ill and missed many classes,he would have made greater progress.含义：He was ill and missed many lessons,so he did not make greater progress.c.表示对将来的假想句型：条件从句 主句一般过去时 should+ 动词原形were+ 不定式 would + 动词原形should+ 动词原形If you succeeded,everything would be all right.If you should succeed,everything would be all right.If you were to succeed,everything would be all right.3.是否 = whether 连接宾语从句I wonder if she is ill.不知她是否病了.