1、情态动词与助动词
1、can能，可以，表说话人同意，许可还可表客观条件许可，如:You can go now.
提建议或请求时可用can I, can you表客气，如Can I buy you a drink?
can和be able to表能力时的区别。
can表一般具有的能力，be able to表在特定条件下的能力，如:Although the driver was badly hurt,he wasable to explain what had happened.
2、may
(1)可以，表说话人同意，许可或请求对方许可。You may go.
(2)(现在和将来)可能，也许，只用于肯定句和否定句中，如He may not be right.
3、must,have to
must表主观上的必须，have to表客观上的必须，如:It's getting late. I have to go. -Must I go now.-Yes,you must.(No, you needn't./ No, you don't have to.)
4、need,dare这二词有实意动词和情态动词两种词性，如用作实意动词后接动词不定式to do，如用作情态动词后接动词原形。Need I go now? --Yes, you must./No, you needn't.)
5、shall用于第一人称疑问句中表说话人征求对方的意见或向对方请求，如，Shall we begin our lesson?用于二、三人称陈述句，表说话人命令、警告、允诺、威胁等口吻，如: You shall fail if you don't workharder.
6、should表应该，意为有责任，有义务。如:We should try our best to make our country more beautiful.
7、will表有做某事的意志、意愿、安心、打算，如"Will you lend me your book?" "Yes, I will."
8、should have done表应该做而未做
must have done表对过去事实的肯定推测
could have done表本可以做某事
9、判断句：肯定句用must,否定句用can't,不太肯定用may,might
He must be in the office now.
He must have gone to bed, for the light is out.
He can't be in the office. He is at home.
He couldn't have cleaned the classroom, because he didn't come here today.
He might be in the office, I am not sure.
He might have cleaned the room, I suppose.
2让步状语从句1、though,although,as的区别
A、Though,although的主句中可以用yet, still, nevertheless,但不可使用but。
B、though引导的从句可以倒装，也可以不倒装;as引导的从句必须倒装;although引导的`从句不能倒装。其结构为：形容词/分词/副词/动词原形/名词(无冠词)+as/though+主语+谓语……
2、though可用作副词，放在句末，意为“不过，但是”。Although无此用法。
3、某些短语也引导让步的从句或短语，意为“尽管”，如：in spite of the fact that, despite the fact that,regardless of(the fact that)
句子种类
1、陈述句的否定
(1)在含有宾语从句的主从复合句中，当主句的谓语动词是think, expect, believe, suppose, guess, fancy,imagine等，且主句主语是第一人称时，宾语从句谓语的否定习惯上要移到主句谓语上，如: I don't think he is right.
(2)含有否定意义的副词never, seldom, hardly, scarcely, rarely, barely的句子应视为否定句，如: I have never been there before.
2、反意疑问句
(1)need和dare既可作情态动词，又可作实意动词，在反问部分须加以区别，如We needn't leave, need we? We don't need to leave, do we?
(2)陈述部分出现否定意义的副词或代词如never, seldom, few, hardly, little等时，反问部分须用肯定形式，如：He seldom comes, does he?
(3)陈述部分用不定代词作主语时，反问部分的主语用it，如：Nothing can stop me, can it?
陈述部分用everybody, everyone, somebody, someone，等作主语时，反问部分常用it，有时也用they，如:Everybody knows that, don't they?
(4)陈述部分包括used to时，反问部分可有两种形式，如: You used to get up early, usedn't (didn't) you?
(5)陈述部分是"there + be"结构时，反问部分用there，如:There's something wrong with you, isn't there?
(6)陈述部分是含有宾语从句的主从复合句时，反问部分的主语和谓语应和主句保持一致，如: He never told others what he thought, did he?
但，如果是I think , I believe等+宾语从句时，反问部分须和从句的动词保持一致，如，I don't think he is right, is he? I don't believe he does that, does he?
3、感叹句
用what或how,
What a beautiful park it is.
How beautiful a park it is.
How beautiful the park is.
How we worked!
4、祈使句
Take care!
Don't stand there.
Please open the door for the old lady.
3不定式的构成1、不定式的一般式：不定式的一般式所表示的动作通常与主要谓语的动作同时或几乎同时发生，或是在它之后发生。
如：They invited us to go there this summer.他们邀请我们今年夏天去那儿。He stood aside for me to pass.他站到一边让我通过。
2、不定式的完成式：不定式的完成式所表示的动作在谓语所表示的动作之后发生，它在句中可作表语、状语、宾语，有时也可作主语、定语等。
如：She seemed to have heard about this matter.她似乎已听说过这件事。
I am sorry to have kept you waiting so long.我很抱歉让你等了这么久。
I meant to have told you about it,but I happened to have an important thing to do.我本来想告诉你这件事的，但我碰巧有一件重要的事要做。
It has been an honor for me to have traveled so much in your country.对我来说，在你们国家旅行这么多地方是一件很荣幸的事情。
3、不定式的进行式：不定式的进行式表示正在进行的与谓语动词同时发生的动作。它在句中可以用作除谓语以外的所有成分。
如：It’s nice of you to be helping us these days.你真好，这些天一直帮我们。
He pretended to be listening to the teacher carefully.他假装在认真地听老师讲课。We didn’t expect you to be waiting for us here.我们没料到你一直在这儿等我们。
4、不定式的完成进行式：如果不定式表示的动作是谓语所表示
5、动词不定式的否定形式是由not或never加不定式构成。如：Try not to be late again next time.尽量下次不要再迟到。He wished us never to meet her again.他希望我们永远不要再见到她。
6、疑问词+动词不定式：不定式和疑问词whether,what,which,whom,where,when,how,why等连用可以在句中起名词的作用，通常跟在tell,know,show,decide,learn,wonder,explain,advise,teach,discuss,find out等动词后面作宾语，有时也可以充当主语、表语等。
如：On hearing the news,he didn't know whether to laugh or to cry.听到这个消息，他不知道该哭还是该笑。
When to hold the meeting has not decided.什么时候开会还没有决定。
The most important problem is how to get so much money.最重要的事情是如何搞到这么多钱。
介词后一般不直接接不定式，但可以接疑问词+不定式短语作宾语。
如：Mary gave some advice on how to learn English.玛丽提了一些如何学习英语的建议。
I have no idea of how to do it.我不知道该怎么做。
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