情态动词，在英文中主要用来表示说话人的看法、态度等。它很接近中文里的能愿动词。从用法上来说，它有这样几个特点：
1)各个情态动词自身都有一定的词义。
2)情态动词不能在句中独立担当谓语。
3)情态动词在句中不受任何人称,性,数变化的影响。
4) 情态动词后接的不定式(除ought外)都不带to ，即接动词原形。
英文中的情态动词主要有：can , could ; may , might ; must ; ought ; need ; dare , dared ，另外，shall , will , should , would在一定的场合也可用作情态动词。例如：
He can speak five languages .他会说五种语言。
She must have arrived home by now .现在她准到家了。
We should study hard for our motherland . 我们应该为祖国而努力学习。
They needn't be in such a hurry for there is enough time
for them . 他们还有足够的时间，用不着这么慌张。
1. 常用情态动词的基本用法
can , could 能，会
(could可以看作是can的过去式，这两个词除了时态不相同外，在表达意思的许多方面是相同的。当然could也有自己独特的用法。)
1)表示脑力或体力上的能力
Nobody can stop the development of science .
谁也无法阻止科学的发展。
She can sing that song in English.她能用英文唱那歌。
He can submerge to a depth of about twenty meters .
他能潜入约二十米深的水中。
He could hardly support his family before he found the new job .他在找到那份新工作前几乎无 法养家。
I could not understand the lecture on the computer given by Mr. Smith .
我听不懂史密斯先生作的那个关于计算机的讲座。
2)表示客观上的可能性
You can borrow this useful book from the library .
你可以从图书馆借到这种有用的书。
A more suitable person than him for the job can not be found . 不可能找到比他更适合这份工作的人了。
Now people can skate on the lake .现在人们可以在湖上滑冰了。
When the storm stopped , the plane could take off .
当风暴停下来时，飞机可以起飞了不得。
3)表示主观上的允许
Can I ask you some questions about it ?
我可以问你有关这件事的几个问题吗?：来源：www.yingyusanji.com
You can not leave here till I come back .直到我回来你才能离开。
Such kind of thing can't happen any more later .
这类事以后不准再发生了。
Can you tell me how to get to the airport ? 你能告诉我怎么去机场吗?
Could you tell me how to get to the airport ?
您能告诉我怎么去机场吗?
Could I be forgiven my negligence ? 请原谅我的疏忽，行吗?
4)(用于否定句、疑问句或感叹句中)表示猜测、怀疑或惊诧
How can / could you be here ? 你怎么会在这儿?
She couldn't / can't be so stupid to do that .
她不可能蠢得去做那种事吧。
He couldn't / can't be over seventy .他不可能有七十多岁了。
Where could / can the boy be now ? 那孩子现在能在哪儿呢?
另外，could还常用于表示较客气委婉的看法、提问及用于虚拟语气的结构中。这时候，could就不可以看作是can的过去式了。而是could自己独特的用法。如：
Could you speak a little slowly ?
您能稍微说慢一点儿吗?
I'm afraid that we couldn't give you any definite answer at this moment .
恐怕我们这时候还无法给予您任何确切的答复。
I could come earlier if asked .
如果要让我早一点来，我可以来早一点。
We would appreciate it if you could offer us any help .
如果您能为我们提供帮助的话，我们将不甚感激。
You could have done better if you had worked harder at it .
如果你再加把劲，本来可以干得更好一些的。
may , might 或许，可能，可以
(might可以看作是may的过去式，这两个词除了时态不相同外，在表达意思的许多方面是相近的。当然may 和might又都有一些各自不同的独特用法。)
1)可能性
I may be busy from tomorrow on .从明天起我可能会忙起来。
You may catch sight of the sunrise from here when you get up before 5 in the morning .你在早晨五点钟以前起来，或许能从这儿看到日出。
I wondered if they might agree with the idea .我想知道他们是否会同意这种想法。
She thought it might be wise to try her luck here .
她认为在这儿碰碰运气也不错。
2)表示允许
May I come in ? 我可以进来吗?：来源：www.yingyusanji.com
I'd like to have a smoke here if I may .
如果可以的话我想在这儿抽一支烟。
The librarian told her that she might return the book to the library in three days .
图书馆理员告诉她说，她可以在三天后还那本书。
At the press conference , a news reporter asked the chairman if she might trouble him with a question about Taiwan issue.
在记者招待会上，一位新闻记者问大会主席她是否能提一个有关台湾问题方面的问题。
3) may间或用来表示祝愿，也常用于表示目的或让步的状语从句中:
May that day come soon .但愿这天早日到来。
May you succeed in winning the first prize in the game .
祝愿你比赛夺冠成功。
May you continue in your efforts and achieve greatersuccesses .
祝愿你继续努力并取得更大的成功。
