if英语语句

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。

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1. (表示条件)如果 ,主句用将来时，if从句用现在时表示将来(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、if作为连词,引导条件状语从句,表示“如果”等.在复合句中如果主句用将 来时,则if引导的状语从句用一般现在时（最基本的）. eg.If it doesn’t rain,we will go to the picnic next Sunday.如果天不下雨,下周日我们将去野餐.二、if还可以引导让步状语从句.在意义上相当于even if,even though或although.这时 if 意为“即使 是”,“虽然”. eg.I’ll do it,even if it takes me a long time． 虽然会花费很长时间,我还是要做这事.If he is little,he is strong.他年纪虽小,力气倒大 三、if作为连词还可以引导宾语从句.引导宾语从句时和whether意思相同.例如： eg.She asked if ／ whether I like it． 她问我是否喜欢它.* 此时注意：1.or not放在whether之后时,只能用whether不用if.2.在强调任意选择时,用whether…or,此时不用if替换whether 3.虽引导宾语从句,但为了强调宾语部分,也可把从句放在句首,此时只用whether 不用if .4.从句作介词宾语时只用whether不用if.5.作discuss等动词的宾语时,用whether不用if.6.句子中有if引导的条件句,如再有表示“是否”的宾语从句,用whether不用if 7.容易产生歧义时用whether不用if来表示“是否”.基本上碰到选择 if 还是 whether 的问题时都选 whether,除了一条：如果宾语从句为否定句时,则 只用if不用whether.eg.I don’t know if it won't rain tomorrow..我不知道明天是不是会下雨 四、if引导时间状语从句,意为“当”或“无论何时”,不含有条件之义时,if从句中的时态与主句中的时 态相同. eg.If you mix yellow and blue,you get green．你将黄色与蓝色混合,便会得到绿色. 五、if后接否定动词,用于感叹句中,表示沮丧、惊奇等.例如： eg.Well,if I haven’t left my homework at home!真倒霉,我把作业落在家里了! 六、用于虚拟语气中,if从句中用过去式,表示不太可能实现或提出作为考虑的假设条件.eg. 1.If I were a bird,I could fly.如果我是只鸟,我就会飞了. 2.If I asked him(if I were to ask him) for a loan,would he agree?如果我向他借款,他会答应吗? 另外,if从句中用过去完成式,表示过去未实现的条件.eg. 1.If they had started earlier,they would have arrived in time．要是他们早些动身,他们便可及时到达了. 2.If they had not started at that time,they would not be here now．如果他们那时不动身,现在他们就不会在此地了. 第三,if 条件句的虚拟有时可省略,然后将主语与所用的限定动词(were,should,had)倒置.eg. 1.Should it (=if it should) be necessary,I will go.倘若有必要,我会去的. 2.Were I(=if I were) in your post,I would do the same ． 如果我处于你的位置,我也会这样干的. 3.Had I(=if I had)known earlier,I wouldn't go．如果我早一点知道,我就会不会走了. 七、if与其它一些介词的连用. as与if连用,意思是：“仿佛、好像”同样引导从句.eg.It isn’t as if he doesn’t know the rules．(ie． He does know the rulers．)他不像不懂规则的样子.(即他懂得规则) （ie=namely=that is to say=in other words：“即,那就是说”） 另外as if还可以引导感叹句.例如： As if I would allow it!(ie．I would certainly not allow it!) 好像我会答应那样!(我才不会答应呢!) * if与only连用.表示“如果...就好了”.例如： 1.If only he arrives in time!他若能及时到达就好了! 2.If only she had known about it!（But she didn’t know.）她那时要是知道（但她不知道）这事就好了!* 此时注意区别 only if...：“只要...”,相当于“if” eg.Only if you word hard,you'll be successful one day.