情态动词must, should, may(might), ought to, can(could), need, would等都可以与动词完成式连用作谓语，其模式为“情态动词 have v-ed”。这类结构表示对过去所发生动作的推测或判断。但是，不同的情态动词所表示的意思又有所不同。
“must have v-ed”表示对过去事情较有把握的、肯定性的推测，常译为“一定”，“准是”，“肯定”。当must用于推测意义时，其否定形式通常不是must not, 而是can/could not.“can’t/couldn’t have v-ed”表示对过去事情的否定性推测，常译为“决不可能”，“不太可能”。
may(might) have v-ed表示从现在看来过去可能发生过某事，没有“must have v-ed”所表示的“逻辑上的必然性”，即“must have v-ed”所表示的说话人推断过去肯定发生过某事。如：
He said I must have done something bad to deserve it.
他说我肯定是罪有应得。
I think we must have taken a wrong turning somewhere.
我觉得我们一定是在什么地方拐错了路。
He must have fallen from a great height.
他肯定是从很高的地方摔下来的。
Since the ditch is full of water, it must have rained last night.
由于沟里满是水，昨晚一定下雨了。He must have known what she wanted.
他一定早已知道她想要什么了。
I can't remember any more ─ I must have lost consciousness.
我想不起来了——我当时一定是失去了知觉。
Some of the older boys must have put him up to it.
那件事准是一些大孩子怂恿他干的。
It couldn't have been me ─ it must have been someone else.
那不可能是我——准是别人。
《牛津高阶英汉双解词典》
The car must have been doing at least 100 miles an hour.
这车速肯定每小时至少100英里。
Your cheque must have got lost in the post.
你的支票一定是邮寄中遗失的。
I must have been insane to agree to the idea.
我肯定是犯傻了，居然同意了这个想法。
I must have been blind not to realize the danger we were in.
当时我一定是眼瞎了，竟然没有意识到我们所处的危险。
I thought he was her husband ─ I must have misunderstood.
我以为他是她丈夫——我一定是误会了。
The thieves must have had someone on the inside helping them.
这些窃贼肯定有内应。
The branch she was standing on must have snapped off.
她当时踩的树枝一定是突然折断了。
She reasoned that she must have left her bag on the train.
她断定准是把包落在火车上了。
Your trip must have been fun!
你这次旅行一定很开心吧！
Judging by the company he kept, Mark must have been a wealthy man.
根据马克所交往的人来判断，他一定是位富翁。
You must have wiped off that programme I recorded.
你一定是把我录制的节目给抹掉了。
Sorry, I must have dialled the wrong number.
对不起，我一定是拨错电话号码了。
‘ I must have made a mistake, ’ she said lamely.
“我一定是弄错了。”她胆怯地说。
Sam was sure that the wallet must have been found by one of the villagers ,but it was not returned to him.
萨姆肯定钱包是被一个村民给拾取了，但是没有人还给他。（新概念2，L45.）
From a heavy gun that was raised,the captain realized that the ship must have been a cruiser.(新概念3，L32)
船长从捞起来的重炮推测这艘船肯定是一艘巡洋舰。
The city at one time must have been prosperous,for it enjoyed a high level of civilization.（新概念3，L3）
这座古城肯定一度很繁荣，因为它享有高度的文明。
You may have read about it in the paper.
你可能在报纸上读到这件事了。
He may have missed the train.他可能没有赶上火车。
Human error may have been a contributing factor.
人为的失误可能是一个起作用的因素。
The contents of the package may have settled in transit.
包裹里的东西可能在运输途中摇密实了。
A bolt may have fallen off the plane's forward door.
飞机前舱门的一个门闩可能脱落了。
He was a contemporary of Freud and may have known him.
他是弗洛伊德的同代人，可能认识弗洛伊德。
We apologize for the delay and regret any inconvenience it may have caused.
我们对此次延误以及因此有可能造成的所有不便表示道歉。
You may have misheard her ─ I'm sure she didn't mean that.
你可能听错她的话了——我肯定她不是这个意思。
The shooting may have been in retaliation for the arrest of the terrorist suspects.
枪击事件可能是对逮捕嫌疑恐怖分子进行的报复行动。
They may have weaponized quantities of anthrax.
他们可能已将大量炭疽制成了武器。
He may have put pressure on her to agree
他可能向她施加了压力，迫使她同意。
He may have been to some of those places
那些地方他也许去过一些。
One of these men may have been the murderer.
他们其中有一个人可能是杀人凶手。
I may have made a mistake in that regard.
我在那一点上可能已经犯了一个错误。
特别注意：
“must have v-ed”也可以在陈述时表示必须完成某件事：To qualify, you must have lived in this country for at least three years.
你必须在这个国家居住至少三年才能享有此权利。《牛津高阶英汉双解词典》
If society is to exist as a unity, its members must have shared values.
社会若要成为一个统一的群体，它的成员就必须有共同的价值观。
can/could not.“can’t/couldn’t have v-ed”表示对过去事情的否定性推测，常译为“决不可能”，“不太可能”。
His mood of deep pessimism cannot have been leavened by his mode of transport — a black cab
他极度悲观沮丧，而他的代步工具——一辆黑色的出租车，丝毫不能舒缓这一情绪。
《柯林斯高阶英汉双解学习词典》
He can't have slept through all that noise.
他不可能在那种闹哄哄的环境里睡好觉。
From her knowledge of Douglas's habits, she feels sure that the attacker can't have been Douglas
根据她对道格拉斯习性的了解，她敢断定他不可能是那个袭击者。
The extent of the damage could not have been foreseen.
损害的程度是无法预见到的。
Police believe his wife could not have administered the poison.
警方认为他的妻子是不可能下毒的。
He could not have seen me yesterday, because I wasn't there.
昨天他不可能见到我，因为当时我不在那里。
She could not have taken these massive doses orally. In the first place, she did not have enough pills.
她不可能口服这么大的剂量，因为她根本没有足够的药丸了。
Winston could not have read the road signs to save his life.
温斯顿怎么也学不会看路标（来保命）。
I really could not have wished for a better teacher
这个老师对我来说是再好不过的了。
《柯林斯高阶英汉双解学习词典》
needn't have done表示：过去不必做某事, 但事实上做了。John went to the station.He need not have done it.(他本不需要做这件事。)need have done表示有必要做，但是没有做的事．You need have told me about it,but you don't,why?
实战练习：
1、Mary’s score on the test is the highest in her class; she____have studied very hard.
A)may
B)should
C)must
D)ought to
2、You____her in her office last Friday; she’s been out of town for two weeks.
A)needn’t have seen
B)must have seen
C)might have seen
D)can’t have seen
3、Mary____my letter; otherwise she would have replied before now.
A)has received
B)ought to have received
C)couldn’t have received
D)shouldn’t have received
4、Dinosaurs are thought to____millions of years ago
A)die out
B)have died out
C)having died out
D)dying out
解析：
1、答案选C。must have v-ed表示推测过去某事一定发生；may have v-ed表示推测过去某事也许发生。Should/ought to have v-ed表示“本应该…”根据句意，C为正确选项。
2、答案选D。can’t have v-ed表示对过去发生事情的否定推测；needn’t have v-ed表示过去做了本不必做的事。根据句意D为正确选项。
3、答案选C。根据本句的后半句otherwise she would have replied before now可知，前半句是一个表示与后半句相应的虚拟过去情况的句子。Can’t/couldn’t have v-ed表示过去不可能发生的事情。所以C为正确选项。
4、答案选B。像be believed/found/known/reported/said/supposed/thought后常跟不定式完成式，表达“据知，据报道”等意思，不定式的动作发生在被动结构(谓语动作)所表示的动作之前。根据语法要求B为正确选项。
