情態(tài)動(dòng)詞顧名思義就是表示情感和態(tài)度的詞，常見的有：can (could); may (might); must; have to; shall (should); will (would); need; dare (dared); ought to; 情態(tài)動(dòng)詞沒有人稱和數(shù)的變化，不能單獨(dú)使用，它與其后的動(dòng)詞原形合成謂語結(jié)構(gòu)。它們的用法如下：
一. can和could 的用法
1. 表示能力或客觀的可能性，還可以表示請(qǐng)求和允許。如：
Can you finish this work tonight? Man cannot live without air.
Can I go now? Yes, you can.
注意：
1) could表示語氣較委婉的請(qǐng)求，主要用語疑問句，(用于此意義時(shí)不用在肯定句)答語用can。
Could I come to see you tomorrow?
Yes, you can. (不能用could). (否定句常用No, Im afraid not.)
2) can表示能力時(shí)，還可以用 be able to 代替，例如：
Ill be able to come this afternoon.
但當(dāng)我們要表示某件事已成時(shí)，須用 was (were) able to不能用could，例如：
He was able to go to the party yesterday evening and he enjoyed himself very much.
2. 表示驚異、懷疑、不相信的態(tài)度。(主要用在否定句、疑問句和感嘆句中)
Can this be true? How can you say like that? This cannot be done by him.
3. can (could) + have + done 的疑問或否定形式表示對(duì)過去發(fā)生的行為懷疑或不肯定。
He cannot have been to that town. Can he have got the book?
二. may 和might 的用法
1. 表示許可，表示請(qǐng)求、允許時(shí)，might 比may 的語氣更加委婉一些，否定回答時(shí)可用cant 或mustnt, 表示不可以、禁止、阻止之意。 例如：
Might I use your pen? No, you mustnt.
May I take this book out? Yes, you can ( No, you cant/ mustnt.)
用May I 征詢對(duì)方許可在文體上較正式，在口氣上比較客氣，在日常口語中，用Can I 征詢對(duì)方意見在現(xiàn)代口語中更為常見。
2. 用于表示祝愿的句子中。例如：
May you success! May you be happy! May you have a good journey!
3. 表示推測(cè)、可能(疑問句中不用于此意)
He may be very busy now. (此句中用might 語氣較弱)
4. May (Might) + have + done 表示對(duì)過去發(fā)生的行為的推測(cè)。例如：
He may not have finished the work. (此句中用might 語氣較更弱)
三. must 和 have to 的用法
1. 表示必須、必要。
You must come on time.
當(dāng)must 引出的問句時(shí)， 若是否定的回答，不能用mustnt，而用neednt或dont have to.
Must we hand in our exercise our books today?
Yes, you must. (No, neednt/you dont have to.)
2. must be + 表語的結(jié)構(gòu)表示推測(cè)，它的否定或疑問形式用can 代替must。如：
He must be our new teacher.
Can he be our new teacher? He cant be our new teacher.
※ 附加疑問句要和謂語動(dòng)詞實(shí)際時(shí)態(tài)一致。如：
He must be our new teacher, isnt he?
3. must + have +done 的結(jié)構(gòu)常用在肯定句中，表示對(duì)過去或完成的情況推測(cè)，它的否定或疑問形式也用can代替must.
He must have finished his work.
※ 附加疑問句也要和謂語動(dòng)詞實(shí)際時(shí)態(tài)一致。如：
He must have finished his work already, hasnt he?
He must have finished his work at four yesterday, didnt he?
4. have to 的含義與must相似，兩者往往可以互換使用，但have to有各種形式，隨have的變化而定，must 與have to有下列幾點(diǎn)不同：
1) must表示的是說話人的主觀看法，而have to則往往強(qiáng)調(diào)客觀需要，例如：
The play is not interesting. I really must go now.
I had to work when I was your age.
2) 兩者的否定意義大不相同。例如：
You mustnt go. (你不可以去) You dont have to go. (你不必去)
3) 詢問對(duì)方的意見時(shí)應(yīng)用must。
Must I hand in the exercise book before eight?
4) must 表示偏偏
Must it rain today? (今天怎么偏偏下雨呢?)
四. dare 和need的用法
1. need表示需要，必須，作情態(tài)動(dòng)詞時(shí)，僅用于疑問句和否定句，在肯定句中一般用must, have to, ought to,或should代替。例如：
You neednt come so early.
Need I clean all the room right now? Yes, you must. ( No, you neednt.)
注意：neednt + have +done表示本來不必要做的事而實(shí)際上做了，例如：
You neednt have waited for me. 你本來沒有必要等我的。
2. dare作情態(tài)動(dòng)詞時(shí)，主要用于疑問句，否定句和條件句中，一般不用于肯定句，例如：
How dare you take my book without permission?
He dare not speak English before such a crowd, dare he?
3. need和dare作情態(tài)動(dòng)詞時(shí)，過去時(shí)形式與現(xiàn)在形式相同(美國(guó)英語中可用dared)。
He was so angry that no one dared say a word.
They said that he neednt stay there any longer.
4. need和dare常用實(shí)義動(dòng)詞，有時(shí)態(tài)、人稱和數(shù)的變化。不同的是dare作實(shí)義動(dòng)詞時(shí)，在肯定句中通常接帶to的不定式，在疑問句和否定句中，dare之后的不定式可帶to或不帶to。例如：
He needs to finish the work before nightfall.
I dare to swim across this river.
He does not dare (to) answer the teachers question.
Dont you dare (to) touch it?
I wonder he dared say that.
5. I dare say是習(xí)慣用語，常可寫為I daresay，用法有以下幾種：
1) 敢于說，通常接that或what引導(dǎo)的名詞性從句。
I dare say that he has stolen Toms football. I dare say what I think.
2) 我想;恐怕;大概;也許是，通常作插入語用，使句子委婉。
I dare say there is something wrong with the machines.
Youre tired, I dare say.
You, I dare say, think otherwise.
3) I dare say往往也作為反語使用。
Oh, you mean to defeat our football team? I dare say you will. (噢!你們想贏我們的足球隊(duì)?也許可以吧。)
五. shall和should的用法。
1. shall用于第一人稱疑問句。表示征求對(duì)方意見。
What shall we do this evening?
Shall I open the window?
2. shall 用語第三人稱疑問句中，表示說話人征求對(duì)方的意見或向?qū)Ψ秸?qǐng)示。
When shall he be able to leave the hospital?
3. shall用于第二、三人稱的陳述句，表示說話人給對(duì)方的'命令、警告、允諾或威脅。
You shall fail if you dont work harder.
He shall have the book when I finish reading.
He shall be punished.
4. should表示勸告、建議、命令，其同義詞是ought to，在疑問句中，通常用should代替ought to.
You should go to class right away.
Should I open the window?
5. should + have +done應(yīng)該做的事實(shí)上沒做;shouldnt have done不該做的事卻已經(jīng)做了，常含有責(zé)備的意思。
You should have started earlier this morning.
You shouldnt have treated her like that.
六. will和would的用法。
1. 用于疑問句表示請(qǐng)求、建議等，would比will的語氣更加委婉。
Will you please give me a hand?
Would you mind my smoking here?
2. 表示意志、愿望和決心。
I will never do that again.
They asked us if we would do that again.
3. 用will be和will have done的結(jié)構(gòu)表示推測(cè)，主要用于二、三人稱，前者表示對(duì)目前的情況的推測(cè)，后者表示對(duì)已經(jīng)完成的動(dòng)作或事態(tài)的推測(cè)。
This will be the book you want.
He will have arrived by now.
4. would可表示過去反復(fù)發(fā)生的動(dòng)作或某種傾向，表示過去習(xí)慣時(shí)比used to正式，同時(shí)它沒有現(xiàn)在已無此習(xí)慣的含義。
I would visit him during my vacation.
The patient would not recover.
5. 表示料想或猜想。
He would be your new teacher.
He would not come any more.
七. ought to的用法。
1. ought to表示應(yīng)該時(shí)意義與should基本一致，但更側(cè)重于一種義務(wù)或責(zé)任。
You ought to take care of him.
Parents ought to bring up their children.
2. 表示推測(cè)，注意與must表示推測(cè)時(shí)的區(qū)別。
He must be home by now.
He ought to be home by now.
This is where she must be.
This is where she ought to be.
3. ought to have done的用法與should have done的用法相同
注意：ought to在美國(guó)英語中，用于否定句和疑問句時(shí)，to可以省略。如：
Ought you smoke so much?
You oughtnt smoke so much.
八. used to; had better; would rather的用法。
1. used to表示過去習(xí)慣動(dòng)作或狀態(tài)，現(xiàn)在已經(jīng)不存在，在間接引語中，其形式可不變。如：He told us he used to play football when he was young.
1) 在疑問句、否定句或否定疑問句中，可有兩種形式。
疑問句：Did you used to/Used you to go to the same school as your brother?
否定句：I usednt to/didnt use to go there. (usednt 也可為usent, 發(fā)音不變)。
否定句疑問句：Usednt you to/Didnt you used to be interested in the play?
2) 在附加疑問句和簡(jiǎn)略答語中，也可有兩種形式。
She used to be very fat, didnt/usednt she?
Did you used to/Used you to play chess? Yes, I did/used to.
2. had better意為最好，后接不帶to不定式。
We had better go now.
Hadnt we better stop now?
I think Id better be going.
You had better have done that.
3. would rather意為寧愿，表示選擇，后接不帶to的不定式。
Id rather not say anything.
Would you rather work on a farm?
Wouldnt you rather stay here? No, I would not. Id rather go there.
由于would rather表選擇，故后面可接than.
I would rather watch TV than go to see than go to see the film.
I would rather throw it away than you should get it.(若than后面接從句常用should do)
Id rather you didnt talk about this to anyone.
※ would rather 還可寫為would sooner/would as soon.
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