mba培訓(xùn)英語(yǔ)復(fù)習(xí)：情態(tài)動(dòng)詞要點(diǎn)分析

（一）情態(tài)動(dòng)詞無(wú)人稱和數(shù)的變化，其后可跟不定式的一般式，也可跟不定式的完成式。can用在否定句中，表示否定的判斷或推測(cè)以及理論上的可能性，其肯定形式為must+原形；could+原形動(dòng)詞表示現(xiàn)在或?qū)?lái)的推測(cè)或判斷。
That can’t be true.
It must be done.
You could be right.
來(lái)源：考試大
（二）can和could可用于下列結(jié)構(gòu)：
can’t help + v-ing
cannot help but不得不
can but只得
cannot choose but只得
cannot…too (over)無(wú)論……也不過(guò)分
One cannot be too careful.
I can but say it again.

（三）can或could與不定式的完成式連用，表示說(shuō)話人對(duì)過(guò)去發(fā)生的行為的真實(shí)性所持的態(tài)度（驚奇或懷疑）。can只用于疑問(wèn)句或否定句。can’t/ couldn’t have + 過(guò)去分詞表示對(duì)過(guò)去情況的強(qiáng)烈否定推測(cè)，一般譯為“一定沒(méi)……”。
Where can she have gone?
She can’t have gone to school. — It’s Sunday.
He could have gone off with some friends.
來(lái)源：考試大
（四）may和might均可表示可能性和許可。may可表示給予許可，might則不能。may用于現(xiàn)在和將來(lái)時(shí)，might用于過(guò)去時(shí)或表示婉轉(zhuǎn)意義，或可能性不大。
She may not be at home. (= It is possible that she is not at home.)
She can’t be at home. (= it is not possible that she is at home.)
Brown might come to sign up for the match 2 days later.
來(lái)源：考試大
（五）may +不定式的完成式表示說(shuō)話人對(duì)過(guò)去發(fā)生的事情的懷疑與推測(cè)；might+不定式的完成式表示對(duì)過(guò)去發(fā)生的事情可能性的推測(cè)，所推測(cè)的可能性有時(shí)與實(shí)際情況相反，一般含批評(píng)、責(zé)備的口吻。可能性最小。
She is late. She may have got up late.
You might have done it better.

（六）must表示義務(wù)時(shí)，其否定式形式為don’t need to, needn’t + V或don’t have to.
You needn’t come to see me if you don’t want to.
You don’t have to talk so loud.
來(lái)源：考試大
（七）must + 不定式的完成式表示對(duì)過(guò)去發(fā)生的事情較有把握的推測(cè)，譯為“一定……”，否定式為can’t have done.
The road is wet. It must have rained last night.
He can’t have finished all the exercises within an hour.
來(lái)源：考試大
（八）ought to 與should + 不定式的完成式用于肯定句，表示該做而未做，用于否定句表示不該做的事而做了，有強(qiáng)烈的批評(píng)與責(zé)備口吻。
You ought to have handed in your homework this morning.
You should not have done such a foolish thing.

（九）needn’t have + 過(guò)去分詞表示做了不必做的事，譯為“其實(shí)沒(méi)有必要……”。
You have five days more. You needn’t have worked so hard.