第1个回答 2011-09-07
表示说话人对某一动作或状态的态度，表示/认为“可能”、“应当”、“必要”等含义，但情态动词本身词义不完全，不能单独作谓语/谓语动词，必须和动词原形（不带to的不定式）连用。情态动词没有人称和数的变化。朗读时，情态动词的肯定式一般不重读。
情态动词的否定式一般是在它们的后面加否定词not构成，如could的否定式是could not, 简写时一般在词尾加-n’t, 如couldn’t; 但shall not的否定式应简写为shan’t(不常用简写形式)。
will, would
will表示“意志”、“意愿”，可用于多种人称。
I will (I’ll) tell you all about it.
We will (We’ll) help him if he asks us to.
He won’t go with us.
will在疑问句中用于第二人称时，表示询问对方的意愿或向对方提出请求。 would是will的过去式，表示过去时间的“意志”、“意愿”，可用于多种人称。表示说话人的意愿或向对方提出请求，语气比will婉转，指现在时间。
I’m going to the library. Will you go with me?
Will you give him a message when you see him?
They said that they would help us.
I promised that I would do my best.
Would you like to join the football club?
I’d like to take a look at that shirt over there.
shall, should
should常用来表示劝告、建议，认为某人“应该”、“应当”做某事， 或“有义务和责任”做某事。
-I have a headache.
-You should go to bed.
You should eat a lot of healthy food.
You shouldn’t watch TV every day.
在疑问句中，shall用来征询对方意见或请求指示，用于第一、三人称。should 作为情态动词，表示“劝告”、“建议”，常译作“应该”。
Where shall I wait for you?
Shall we start the meeting now?
You should keep your promise.
Young people should respect old people.
can, could :
表示“能力；许可；可能性”等。could可以代替can表示语气较为婉转。在口语中can可以代替may表示许可，而may比较正式。
I can speak English and a little French. (能力)
Can we eat in school? (许可)
Could I watch TV? (许可)
Could you take out the trash? (可能性*)
Some of us can use the computer now, but we couldn’t ten years ago. (能力)
Can/Could I borrow your bike for a moment? (许可)
He said I could use his computer. (许可)
I thought the story could not be true. (可能)
may, might
表示许可或征询对方许可，有“可以”的意思。用作此意时，它的否定形式可以用may not, 但表示“不可以”、“禁止”、“阻止”等意思时常用must not (mustn’t) 代替代may not.
You may go now.
He said that I might use his telephone.
-May I go with my friends to the harvest festival?
-Yes, you may. / No, you mustn’t. / No, you may not. / No, you’d better not.
表示可能性，有“或许”、“可能”意思，may或might + 动词原形都可表示可能性。用might则语气更加不肯定。
He may / might be from Canada.
They may / might have a lot of work to do.
以上红色助动词只有过去式，没有过去分词 (其他的助动词待确定)
dare
But as the moon gave far too much light, I didn’t dare open a window.
具有情态动词和一般动词两种用法，通常与一般动词一样构成否定句和疑问句，后接带to的不定式，最常用于否定句中。如：
I didn’t dare to go.
He won’t dare to break his promise.
dare 亦可作情态动词，在英国英语中尤用于现在时否定式，后接不带to的动词不定式。
I daren’t tell her the news.
在口语中，该词的各种形式(我认为指的是“一般动词”和情态动词)常与不带to的不定式连用。如：
Don’t you dare tell her what I said! 你敢告诉他我说的话！
I didn’t dare look at him.
ought (否定式ought not to / oughtn’t to；疑问式为Ought I / you to …?)
无人称和时态的变化，后接带to的动词不定式。 ought to 可表示“义务”、“要求”或“劝告”，常译作“应该”、“应当”等（和should差不多，只是语气稍重一些）；有时表示“非常可能”的意思
There’s something I ought to tell you before you leave.
He ought not to do that.
-Ought he to see the doctor?
-Yes, he ought to.
If she is completely well, she ought to be back at school today.
used to
had better
must（没有过去式）
表示“必须”、“应该”。否定式must not / mustn’t 表示“不应该”、“不许可”、“不准”、“禁止”等。在回答带有must的问句时，否定式常用need not / needn’t 或 don’t have to, 表示“不必”，而不用must not。 表示“一定”、“必定”等推测意义时，一般只用在肯定句中。
You must eat less meat.
You mustn’t speak like that.
-Must I be home before eight o’clock?
-Yes, you must.
-No, you needn’t. / No, you don’t have to.
The work must be finished as soon as possible.
You mustn’t smoke in public places.
There must be something wrong.
I don’t like this radio. I must buy a new one.
The radio is broken. I have to buy a new one.
have to（过去式：had to）
表示“必须”、“不得不”。在这个意义上与must很接近，但must表示的是说话人的主观看法，而have to表示的却是客观需要。have to比must有更多的形式。
I must go now. (主观看法)
I have to go now. (客观需要)
You don’t have to worry about that.
You have to wear sports shoes for your gym class.
Every student will have to know how to use computers.
其他：
You have got to go now. (我造的句)
Have you got to go now?（书上句子）
will have to
need
The bell rings so you need to go to class. (这里need应该是实义动词)
“I need to pack up my things in the suitcase very quickly,” the girl said. (这里need应该是实义动词)