991 c．表示“肯定存在的情况”，可译为“一定……”。must be，“must be＋-ing”或“must＋表示状态的动词”表示现在或一般的情况，must have表示过去情况，“must＋表示动作的动词”表示将来情况（这样用时，must和969节中所谈may的用法相似）。
He must be（=is surely）very busy today．（=I am very certain he is very busy today．）
That man must be a chemist．
He must need（or must of necessity，must inevitably）be very sad after the loss of his wife．
He must be at the restaurant now．
This plan must be something．
Nobu must be enjoying himself in Tokyo now．
He must be living in the country this month．
He must be coming this moment．
He must know many important persons．（must＋表示状态的动词）
This countryhouse must belong to John．
She must remain single until today．
A man with such a face must appear very proud to strangers．
Mr．Kim must have come from Seoul．（=I am［or was］very sure that Mr．Kim came from Seoul．或I am very sure that he has come from Seoul．）
Rama must have studied in Calcutta．He was（or is）a historian．
He must have been very ill．He looked（or looks）so pale．
I cannot find my key．I must have lost it when I was buying a newspaper．
He was very sad．He must have seen（=had certainly seen）something unpleasant．
Hunger must（=will certainly）follow after the long drought．（must＋表示动作的动词）
You must win，if you do your best．
It must snow today．
992 d．可用在表示现在、将来或一般情况的虚拟条件句中，可用在主句中，也可用在从句中。
If I had to（用来代替must或have to）marry him（条件从句），I should quarrel with him everyday．
If I were obliged to（用来代替must）say something about the city，Ishould offend some people．
If it had not been for John，Mary must（=would surely）have lots of trouble（主句）.
If we were not careful enough，things must be worse．
If he should abandon her，she must go mad．
If he were in Egypt，he must see the Pyramids．
If I were to live alone on this island，I should have to（=should be obliged to）work very hard（主句）.
If she called on me，I should have to prepare something to entertain her．
993 e．Had had to和must have可用在表示过去情况的虚拟条件句中，可用于主句和从句。
If I had had to（or had been obliged to）marry him，I should have quarralled with him every day．（had had to用得很少）
If I had been compelled（or forced）to steal those diamonds，I should have made great mistakes and been caught．
If he had abandoned her，she must have（=would surely have）gone mad．
If he had been in Egypt，he must have seen the Pyramids．
If I had been to live alone on this island．I should have had to（or would have been obliged to）work very hard．
If she had called on me，I should have had to（or should have been obliged to）prepare something to entertain her．
9．Ought to
994 助动词ought to表示责任、推想等。
995 a．表示该做的事、理应做的事，可译为“应该”“应当”。
You ought to work hard．（=It is your duty to work hard．）
He ought to listen to you．
You ought to see the film．（=It is profitable for you to see the film．）
We ought to buy things more expensive but more durable.
I think I ought to speak to her mother about the marriage.
在美国，在否定句及疑问句中，to有时省略。
You ought not（to）（=It is improper for you to）talk too much．
You ought not（=have no business to）ask me about her．
What ought I do if I oughtn't smoke?
下面两句为不规范用法：
He had ought to（or should ought to）（=ought to）（不规范用法）be here today．
Such things don't ought to（=ought not to）（不规范用法）be said here．
在间接引语中，ought可以表示各种不同时间。
He says that you ought to write the letter．（现在）
He said that you ought to write the letter．（过去）
He will say that you ought to write the letter．（将来）
He does not think I ought to leave the company．
It is supposed every citizen ought to observe the law．
He said I ought to work hard，and who ought not?
He knew everything about me．I ought to leave the company as soon as possible．
He will think I ought not to be his wife．
Ought I to grumble?
Ought to have表示在更早的时间应该如何。
He says that you ought to have written the letter．
He said that you ought to have written the letter．
He will say that you ought to have written the letter．
I know he ought to have done it last Sunday．
He ought to have sent the letter．I still see it on the desk．
He came last Saturday．But he ought to have come two days before．
He ought to have started．It was too late．
You will say one day that you ought to have married another girl．
I shall never say I ought to have done this or that．
He resigned and many of his friends think he ought to have done so．（He did resign．）
He ought to have left the city ten days ago，as he actually did；for only five days ago the war broke out．（He did leave it．）
在多数情况下，ought to have表示一个与过去事实相反的情况。
He suffered a great loss．He ought to have followed my advice．（But he didn't．）
Seven were killed in the traffic accident．They ought to have driven slower．（But they did not．）
He ought to have kept silent．
You ought not to have laughed at him．（But you did laugh．）
由于ought前不能加will，要清楚表示是将来情况，常常须用别种说法。
It will be your duty to take care of the child．
I shall have no business to advise you again．
注：ought to和should的意思很相近。用ought时语气更严肃一些，这时多指按道义、法律、身体情况，应当如何。用Should时语言更亲切一些，这时表示讲话人的关心。为了避免使对方感到不自在，常可用should代替ought to。
996 b．表示推理，有时也译作“应当”。
Since it has rained almost a week，we ought to（=should）have fine weather now．（现在情况）
He ought to（=should，normally）be able to speak Japanese．He has lived in Japan ten years．
He was an expert，so his information ought to be reliable．（过去情况）
He was a tiger among his friends．What ought he to be among his employees?
He ought to have arrived by this time，for it is already noon．（现在以前已完成的动作）
You ought to have finished your work by now．
He ought to have got married．He was forty．（过去某时前应已发生的情况）
He had done business many years．He ought to have saved some money．
10．Need，Needed
997 Need的意思是“需要”，可以用作主要（及物）动词。这样用时，如果主语是第三人称单数，后面要加-s词尾，后面若跟不定式，要加to。
He needs（=requires，wants）my help．（用名词作宾语）
Does the rice-field need rain?
The watch needed repairing.（用动名词作宾语）
The child needs spanking．
The watch needed to be repaired.（用不定式作宾语）
The child needed to be spanked．
He needs John to help him．（用“名词＋补语”作宾语）
He needs（=is required）to start earlier．（现在时）
He doesn't need to start earlier．
Does he need to start earlier?
He needed to start earlier．（过去时）
He didn't need to start earlier．
Did he need to start earlier?
He will need to start earlier．（将来时）
He won't need to start earlier．
Will he need to start earlier?
998 Need也可用作助动词，这时不加-s词尾，可跟不带to的不定式。它用在下面几种情况中（need作助动词用时不如作及物动词用时多）：
(1)用在否定句中。
“Must I go now?” “No，you need not go（=It is not necessary for you to go）.”（Need not很常用）
You need not say anything．
He need scarcely（or hardly）advise me．
You never need tell me this or that．
Nobody need help me．
(2)用在含有否定意义的句子中。
He need only wait here．（=He need not do anything else．）
You need but consider the matter to understand its importance．
He comes oftener than he need．（=He need not come so often．）
I don't think he need come．（=I think he need not come．）
That is all that need be said．（=I need not say anything else．）
There is no more that need be said．（No more need be said．）
(3)用在疑问句中。
Need he say it again?
Need you go at once?
You needn't go，need you?
Why need I worry?
What else need he do?
(4)用在if，unless，whether引起的从句中。
If he need come，he will．
I wonder whether I need see her．
999 助动词need不能用在肯定句中。在肯定句中要用其他形式表达同样的意思。
He needs to start earlier．（用主要动词need）
He must（or have to）start earlier．
“Need he come?” “No，he need not．”“Yes，he must．”
“Yes，he needs to．”
1000 助动词need可用来表示过去情况，过去时间可由一时间状语表示出来，也可由另一过去时动词表示出来。
He need not come yesterday．
Need he come last Sunday this time?
He told me I need not work so hard．
He advised me to take care of my health，but I said he need not worry.
She need not go if he decided to go instead of her．
He already told you everything．What else need he say?
He was as clever as need be（=extremely clever）.
注：可以用主要动词的否定形式（did not need to或needed not to）代替助动词need的否定形式（need not），如：He did not need to come yesterday．或He needed not to come yesterday．后一种形式很少用。
1001 将来时只能由带to的形式表示。
He will never need to work for anyone．
I shall need to say nothing．
1002 Need也可用在虚拟语气中。
If money were useless，we need not struggle for it．（现在情况）（But we must struggle for it．）
If you had been careful enough，you need not have suffered．（过去情况）（But you had to suffer．）
You need not have worried．（过去情况）（But you did worry．）
比较：You did not need to worry．（You did not worry．）
You need not have fired him．（But you did．）
比较：You did not need to fire him．（You did not．）
He talked more than he need have done．（=He talked more than necessary．）
The room was bigger than it need have been．
He was more honest than he need have been．
Need he have come so early?
1003 Needn't可以由其他说法代替。
I don't have to（or haven't got to）answer him．
I have not need to say much．
I have no need（or no occasion，no call）to flatter anyone．
He is not bound（or required，called upon）to do anything for anyone．
1004 Need not be和need not have可以表示“不一定”，而must be和must have的意思正相反，表示“一定……”。
试比较下面句子：
He is poor and he must be（=is certainly）dishonest．
No，he need not be dishonest．（=He may be dishonest，or not．）
He must be sixty．
No，he need not be sixty．（He may be sixty，or not．）
He has been to England，but he need not have（=may have or may not have）visited Shakespeare's native town．
He need not have seen much of the world，though he is an old man．
11．Dare，Dared
1005 Dare作为主要动词，有3种意思：（1）敢于面对；（2）向……挑战；（3）敢于……。如果主语为第三人称单数，它后面应带-s词尾；如果跟不定式，可以跟to，也可以不跟。
(1)He dares any danger．（跟名词或代词）
(2)He dares me to fight．（跟名词或代词＋不定式）
(3)He does not dare（to）jump down．（现在）
Does he dare（to）jump down?
He dares（to）jump down．
He did not dare（to）jump down．（过去）
Did he dare（to）jump down?
He dared（to）jump down．
1006 作为助动词，dare只有一个意思，就是“敢于”。它不加-s词尾，也不跟to。它用于下面5种情况：
(1)用于否定句。
He dare not contradict me．（常用）
I dare not criticize anybody．（常用）
He never dare touch me．
No one dare ask him about his past．
(2)用于有否定意思的句子。
I don't think he dare come．
(3)用在疑问句中。
Dare he climb the tree?
How dare you read my letter．（常用）
You daren't speak to her，dare you?
(4)用在if，unless等引起的从句中。
I wonder if he dare see me again．
(5)用在某些肯定（陈述）句中。
He dare say anything they don't like，and he dare do anything he thinks right．
I dare say（=I think），he is right．（常用）
上面例句都是现在时，下面是过去时的例子：
(1)He dared not go．（带not的否定句）
Nobody dared to go．（这3个句子用带to的结构）（带to比不带to的结构用得多）
Neither dared to go．
He scarcely（hardly）dared to go．
(2)We kept silent and we dare not say anything．（在和一个过去时动词一起用时，dare可用作过去时）
I told him I dare not go．
He was so bad-tempered that I dare not talk with him．
(3)Dared he strike you?
How dared you say that?
(4)I wondered if he dared do it again．
(5)I dared do anything to achieve my purpose．
1007 在前面有shall，should，will，would或has，had等助动词时，dare后面需加to。
I shall not dare to go there again．
He would never dare to see me．
He has never dared to ask me about it．
1008 Dare和dared也可用在虚拟语气中。
If I dared（to）fight，I could kill him．（But I dare not．）
If I dare fight，I could kill him．
He daren't（=would not dare to）say that，if I were there．（But I am not there，so he dares to say that．）
He daren't have insulted（=wouldn't have dared to insult）anyone if he had considered it．
He daren't（or daredn't）have touched you if you had been rich．
12．Used to，Use to
1009 助动词used to或use to可用来表示过去的情况。
We used to live in Japan．（But we are not living there now．）
They used to think they were always right．（But they do not think so now．）
There used to be a big tree in front of the temple．
He usedn't to tell lies．（书面体）（说He never used to tell lies．更好一些）
Used you to drink wine?（书面体）（说Did you use to drink wine?更好一些）
What used you to eat?（说What did you use to eat?更好一些）
They used to visit this tea-house，usedn't they?（说didn't they?更好一些）
He did not use to play with us．（口语体）
Did you use to read newspapers?
It usen't to be here．Usen't he to be your friend?
He said he used to go to church．
I knew he used to get drunk．
He used to be told so．
It used to be neglected．
13．形式小结
1010
疑问句 肯定和否定回答
Can you make it? I can make it．
I cannot make it．
Can this be true? It must be true．（=I am sure it is true．）
It cannot be true．（=I am sure it is false．）
It may be true；it may not be true．（=I am not sure．）
Must I pay you? You must pay me．
You need not pay me．
Must it be true? It must be true．（=It cannot be false．）
It need not be true．（=It may be false．）
May I take it? You may take it．
You must not take it．
Need he come? He must come．
He need not come．
Used you to live here? I did．
I never used to．
14．Can，May，Must的替代说法
1011 Can，may，must不能用在另一助动词后，更不能用于can，may，must，need，shall，will，have这些助动词后。不能说He may can do it．这时就需要用它们的替代说法。例如，can可以用be able to代替，may可以用have permission to或be allowed to代替，must可以用be obliged to或have to代替。跟这类代替说法连用时，may表示“可能……”，cannot表示“不可能……”，must表示“一定……”，need not表示“无须……”，will，shall，have还是通常的意思。
He may have permission to（代替may may）enter this school．（It is probable that he may enter this school．）
He may be able to（代替may can）read this．（It is probable that he can read this．）
He may have to（代替may must）do it over again．
He cannot have permission to（代替cannot may）enter this school．（It is impossible that he may enter this school．）
Can he be able to（代替can can）do it?（Is it possible that he can do it?）
He must have permission to（代替must may）enter this school．（It is certain that he may enter this school．）
He must be obliged to（代替must must）do it over again．（It is certain that he must do it over again．）
He need not have permission to（代替need not may）enter this school．（It is not certain that he may enter this school．）
He need not be able to（代替need not can）read this．（It is not certain that he can read this．）
I shall be permitted to enter this school．
I shall be obliged to do it over again．
He will be able to read this．
He will have to do it over again．
He has been permitted to enter this school．
He has been able to read this．
1012 Can，may，must的这类替代说法还可用于非谓语动词形式，在这类情况下，can，may，must本身是不能用的。
Permitted to（代替may）enter，John was overjoyed．（用作分词）
Being able to（代替can）speak six languages，he found it easy to obtain a job．
Having to（代替must）do many things that morning，he went to the office earlier than usual．
