1、can
1)表能力時(shí)意味著憑體力或腦力或技術(shù)等可以無(wú)甚阻力地去做某事。
I can climb this pole. 我能爬這根桿子。
He is only four, but he can read. 他只有4歲，但已認(rèn)得字了。
2)表示推測(cè)語(yǔ)氣的用法時(shí)，can只能用于疑問(wèn)句和否定句，用于否定句的時(shí)候必須要有充分的理由說(shuō)明。如：
Can he be at home? No, he can't be at home, because I met him in the street just 5 minutes ago.
他可能在家嗎?不，他不可能在家，因?yàn)槲?分鐘之前才在街上遇到他。
2、may (might)
1)表示請(qǐng)求、可以、允許。
You may drive the tractor. 你可以開(kāi)那臺(tái)拖拉機(jī)。
2)表建議(可和as well 連用)
You may (might) as well stay where you are.
你還是原地待著好。(may as well 有“還是……的好”的含義)
3)表可能(事實(shí)上)?？梢灾高^(guò)去時(shí)間，也可以指現(xiàn)在時(shí)間，但語(yǔ)氣更加不肯定，只能用于肯定句和否定句。
He may be at home. 他可能在家。
She may not know about it. 她可能不知道這件事。
He was afraid they might not agree with him. 他擔(dān)心他們可能不同意他的意見(jiàn)。
They might be having a meeting, but I'm not sure. 他們有可能在開(kāi)會(huì)，不過(guò)我不肯定。
3、must
1)表示必須、必要
We must do everything step by step. 我們必須按部就班地做一切事情。
2)must 的否定式有兩個(gè)：當(dāng)回答由must引起的問(wèn)題時(shí)，否定答復(fù)要用needn't或don't have to表示“不必”、“無(wú)須”、“用不著”
3)表示推測(cè)語(yǔ)氣的用法，意為“準(zhǔn)是、一定”等，只用于肯定句，并且要有充足的理由說(shuō)明。
He must have passed the exam, because he looked so happy.
他一定通過(guò)考試了，因?yàn)樗雌饋?lái)如此的開(kāi)心。
4. have to
have to的含義與must是很接近的，只是have to 比較強(qiáng)調(diào)客觀需要，must著重說(shuō)明主觀看法。
I must clean the room.(主觀想法)I have to clean the room.(客觀需要)
另外，have to 能用于更多時(shí)態(tài)：
We had to be there at ten. 我們得在十點(diǎn)鐘到那里。
We will have to reconsider the whole thing. 這一切我們將不得不重新加以考慮。
have to 的否定式：don't have to do 表示“不必做……”之意。
5、would
1)表意愿。
They would not let him in because he was poorly dressed. 他們不讓他進(jìn)去因?yàn)樗轮婆f。
I said I would do anything for you. 我說(shuō)過(guò)我愿意為你做任何事。
2)表過(guò)去反復(fù)發(fā)生的動(dòng)作或過(guò)去的一種傾向。
Every time she was in trouble, she would go to him for help.
她每遇到麻煩都會(huì)向她求助。他告訴我盒子打不開(kāi)了。
6、ought to
表義務(wù)，意為“應(yīng)該”(因責(zé)任、義務(wù)等該做)，口氣比should稍重。
You are his father. You ought to take care of him. 你是他父親，應(yīng)當(dāng)管他。
You oughtn't to smoke so much. 你不應(yīng)該抽這么多煙。
7、used to
表示過(guò)去的習(xí)慣動(dòng)作或狀態(tài)，現(xiàn)在不復(fù)發(fā)生或存在。疑問(wèn)式和否定式有兩種。
He used to live in the countryside, but now he lives in the city.他過(guò)去住在鄉(xiāng)下，現(xiàn)在住在城里。
There used to be a building at the street corner, but it has been pulled down.
街道拐角處過(guò)去有座樓房，現(xiàn)在拆了。
I usedn't (didn't use) to smoke. 我過(guò)去不抽煙。
Used you (Did you use) to go to school on foot? 你過(guò)去常步行去學(xué)校嗎?