(1)must have +过去分词，表示对已发生情况的肯定推测，译为“(昨天)一定……”。如：
My pain must have been apparent the momentI walked into the room, for the first man I met asked sympathetically: “Are youfeeling all right?”
(2)can’t/couldn’t have +过去分词，表示对已发生情况的否定推测，译为“(昨天)一定没……”。 如：
Mary couldn’t have received my letter;otherwise she would have replied before now.
(3)may/might have +过去分词，表示对已发生的事情做不肯定、可能性很小的推测，或事实上根本没发生，译为“也许……”。如：At FloridaPower’s Crystal River plant, a potentially serious leakage of radioactive watermay have been unknowingly caused by an electrician.
As it turned out to be a small house party,we needn’t have dressed up so formally.
(2)should /should not have +过去分词，表示应该做某事但实际上未做，或本不应该做但实际上做了, 译为“本(不)应该……”。如：I regrethaving left the work unfinished; I should have planned everything aheadcarefully.
(3)ought to have+过去分词，表示动作按理该发生了，但实际上未发生，译为“该……”，与should的完成式含义类似。如：
The porter ought to have called thefire-brigade as soon as he saw the fire in the stock, which went up in smoke.
What you said is right, but you could havephrased it more tactfully.
(5)may/might have + 过去分词，表示过去可以做但实际未做，译为“(那样)也许会……”。如：
It might have been better to include morepunchy statistics and photos of equipment in the introduction to further assistfirst-time office automation managers.
(1)may/might (just) as well“不妨，最好”，与had better相近。如：
Since the flight was cancelled, you mightas well go by train.
You cannot be too careful when you drive acar.
The final chapter covers organizationalchange and development. This subject cannot be overemphasized.
(3)usedn’t或didn’tuse to为used to (do)的否定式。
I didn’t expect that he should have behavedlike that.
should do / were to do
如：If the doctor had been available, thechild could not have died.
There is a real possibility that theseanimals could be frightened, should there be a sudden loud noise.
Had it not been for the timely investmentfrom the general public, our company would not be so thriving as it is.
Had Paul received six more votes in thelast election, he would be our chairman now.
Your math instructor would have been happyto give you a make-up examination had you gone and explained that your parentswere ill at the time. (句子前半部分为假设情况，而“父母病了”是事实)
I would have gone to visit him in thehospital had it been at all possible, but I was fully occupied the whole oflast week. (前半部分为假设，后半部分是事实)
desire, advise, recommend, command, direct,order, ask, demand, request, require, insist, maintain, move, propose, prefer,urge, vote。如：
In the past men generally preferred thattheir wives work in the home.
I move that he be discharged for hisserious mistake.
advisable, desirable, insistent,preferable, urgent, appropriate, compulsory, crucial, essential, imperative,important, necessary, obligatory, possible, probable, proper, vital, advised,arranged, commanded, demanded, desired, ordered, proposed, recommended,requested, required, suggested。如：
The board deem it urgent that these filesshould be printed right away.
It is essential that all these figures bechecked twice.
insistence, preference, recommendation,suggestion, proposal, motion, desire, requirement, request, order, necessity,importance, regulation, rule, resolution, understanding。如：
John Wagner’s most enduring contribution tothe study of Afro-American poetry is his insistence that it be analyzed in areligious, as well as worldly, frame of reference.
They keep telling us it is of utmostimportance that our representative be sent to the conference on schedule.
(1)连词but, but that,or, or else;副词otherwise, unfortunately等表示转折假设。如：
A safety analysis would have identified thetarget as a potential danger. Unfortunately, it was never done.
Victor obviously doesn’t know what’shappened; otherwise he wouldn’t have made such a stupid remark.
(2)介词短语暗含假设条件，常用的有：without,but for, under more favorable conditions等。如：
But for the English examination I wouldhave gone to the concert last Sunday.
+不定式一般式暗示虚拟语气。如：Iintended to have called on you, but I was busy at that time.
(4)情态动词完成式暗示虚拟语气。如：Ishould have called to make an airline reservation, but I didn’t.
would rather would as soon as thoughsuppose…
had rather would sooner as if supposing…
If only… It is (high) time that…(从句中动词只用过去式)
如：His wife would rather they didn’t talkabout the matter any more.
I’d rather you went by train, because Ican’t bear the idea of your being in an airplane in such bad weather.
If I were in a movie, then it would beabout time that I buried my head in my hands for a cry.
My father always talks as though he wereaddressing a public meeting.
(2)If it were not for… (与现在事实相反)
If it had not been for… (与过去事实相反) 相当于but for。如：
If it had not been for his help (= but forhis help), we would not have succeeded.
If only the committee would approve theregulations and put them into effect as soon as possible.
(4)lest/for fear that/in case 从句谓语用(should+)动词原形。如：
The mad man was put in the soft-padded celllest he injure himself.
Church as we use the word refers to all religiousinstitutions, be they Christian, Islamic, Buddhist, Jewish, and so on.
The business of each day, be it sellinggoods or shipping them, went quite smoothly.
(1)以 “a” 开头的形容词如alone, alike, asleep, awake等不能做前置定语，可做表语或后置定语。
(2)某些以副词词缀 “-ly” 结尾的词是形容词，如friendly, leisurely, lovely等。
(3)下列动词既是实义动词又是系动词，注意用做系动词时，要求形容词做表语：remain, keep, become, get, grow, go, come, turn, stay, stand, run,prove, seem, appear, look。
Do you enjoy listening to records? I findrecords are often as good as, or better than an actual performance.
On the whole, ambitious students are morelikely to succeed in their studies than are those with little ambition.
The number of registered participants inthis year’s marathon was half that of last year’s.
Young readers, more often than not, findthe novels of Dickens far more exciting than Thackeray’s.
(3)比较级的修饰语如 alittle, a lot, the, any, even, far, hardly, lots, much, rather，还有表示倍数比较的词等，他们的位置是：修饰语+as…as…, 或修饰语+more…than…。如：
Smoking is so harmful to personal healththat it kills seven times more people each year than automobile accidents.
“Do you regret paying five hundred dollarsfor the painting?” “No, I would gladly have paid twice as much for it.”
inferior，minor，senior，prior，preferto，superior，major，junior，preferable，differfrom，compared with，incomparison with，different from，ratherthan。如：Their watch is superior to all the other watcheson the market.
any other +单数名词
the other +复数名词
上述词是用来将比较级结构转变成最高级意义的关键词语，切不可遗漏，否则会造成逻辑混乱的错误。如不能说：John runs faster than anyone.注意与汉语表达的不同。
(1)not so much…as…与其说……不如说……
The chief reason for the population growthisn’t so much a rise in birth rates as a fall in death rates as a result ofimprovements in medical care.
(2)no/not any more…than…两者一样都不……The heart is no more intelligent than the stomach, for they areboth controlled by the brain.
There is no reason they should limit howmuch vitamin you take, any more than they can limit how much water you drink.
(3)no /not any less…than…两者一样都……She is no less beautiful than her sister.
(4)just as…so….正如……，……也……(用倒装结构)Just asthe soil is a part of the earth, so is the atmosphere.
如：Each cigarette a person smokes does someharm, and eventually he may get a serious disease from its effect.
It was during the 1920’s that thefriendship between the two American writers Hemingway and Fitzgerald reachedits highest point.
that指代不可数名词和单数可数名词(如是复数，用those)，后面通常跟有修饰语，如出现在比较结构中的that of。如：Conversation calls for a willingness to alternate the role ofspeaker with that of listener, and it calls for occasional “digestive pauses”by both.
No bread eaten by man is so sweet as thatearned by his own labor.
one指代不确指的单数可数名词，复数为ones。the one 指代确指的单数可数名词。如：
A good writer is one who can express thecommonplace in an uncommon way.
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