情態(tài)動(dòng)詞所表達(dá)的可能性程度：must/can't  should/shouldn't  might/may (not)
另外兩個(gè)"類情態(tài)詞的形式："need/needn't; have to/don't have to
 最自然的虛擬狀態(tài)：由should/would+原型時(shí)態(tài)（不含時(shí)間只含狀態(tài)）
本質(zhì)上是過(guò)去將來(lái)時(shí)：即,時(shí)間固定在過(guò)去將來(lái),狀態(tài)不同：一般、進(jìn)行、完成、完成進(jìn)行.
這時(shí)"虛擬語(yǔ)氣"的產(chǎn)生往往是因?yàn)槲覀円磉_(dá)"本來(lái)應(yīng)該……"（而現(xiàn)在卻還沒(méi)有……）
（本來(lái)可以……,本來(lái)能……）
I should go! (… but I'm still here!) (一般)
I should be working now! (進(jìn)行)
I should have practiced more (than I did)! (完成)
我應(yīng)該多多練習(xí)!（言下之意,現(xiàn)在我練習(xí)得不多.）
I shouldn't dream away my time too much! (完成的否定)
(actually I did dream away my time too much!)
It shouldn't have been leaking for such a long time! (完成進(jìn)行)
I may/might/could have finished! (完成)
一些常見(jiàn)的句型中,就會(huì)出現(xiàn)這種虛擬語(yǔ)氣,而處于從句之中,should 常常被省略掉
o suggest, advise, propose, recommend, plan;
o demand, order, direct, arrange, command, decide;
o require, request;
o think, expect, believe, insist, suspect.
由于他們的含義中包含"建議,假設(shè),應(yīng)該"這類的含義,所以,由他們引起的從句中,就會(huì)包含有should+原型時(shí)態(tài)構(gòu)成的虛擬語(yǔ)氣.
這些動(dòng)詞（以及他們的名次形式,分詞形式）引起的從句還有其他的變形：
主語(yǔ)從句,表語(yǔ)從句,同位語(yǔ)從句
It's suggested that…
My suggestion is that…
The only suggestion that...
The only suggestion I can give you now is that…
一些形容詞引起的表語(yǔ)從句中,也會(huì)有同樣的情況
important; necessary; essential
It's natural ; strange; incredible that
a pity; a shame; no wonder
 由lest, for fear that, in case 引起的從句中多使用should
 表達(dá)與事實(shí)相反
1. 與現(xiàn)在相反：使用[過(guò)去時(shí)]：
I wish I were not here! (一般現(xiàn)在一般過(guò)去)
Suppose we were not here.
He loved me as if I were his own son. (一般現(xiàn)在一般過(guò)去)
Hope I weren't always losing things! (現(xiàn)在進(jìn)行過(guò)去進(jìn)行)
If only/If I hadn't been there! (現(xiàn)在完成過(guò)去完成)
What if I hadn't been waiting right here! (現(xiàn)在完成進(jìn)行過(guò)去完成進(jìn)行)
?？季湫停篒t's (high) time (that)…; would rather (that)…
這兩個(gè)從句,只能表達(dá)對(duì)現(xiàn)在的看法,所以,從句中只有一般過(guò)去時(shí).
2. 與過(guò)去相反：過(guò)去完成時(shí)；
How nice it is if I had past the test!
How nice it is if I had slept a little more this morning!
3. 與將來(lái)相反?將來(lái)的事情沒(méi)有發(fā)生,所以只能推測(cè).
If it rains tomorrow, we'll have to stay one day more.
不過(guò),由于可以用be to表示將來(lái)；所以,虛擬語(yǔ)氣中經(jīng)常出現(xiàn)were to；也是CET-4的?？颊Z(yǔ)法點(diǎn).
 虛擬條件句
o if 部分,做一個(gè)與事實(shí)相反的假設(shè)（所以只有一般過(guò)去和過(guò)去完成）；
o 主句部分,這是表示基于這個(gè)假設(shè)的推測(cè),一般使用情態(tài)動(dòng)詞would,少數(shù)情況下使用could/might/may.
o 注意：兩個(gè)部分之間,是有邏輯關(guān)系,而在兩部分的謂語(yǔ)動(dòng)詞時(shí)態(tài)上,沒(méi)有必然的聯(lián)系.
 注意,虛擬條件句中的if可以省略,造成were/had提前,產(chǎn)生倒裝.
 隱含的非真實(shí)條件
What would you do with 50 thousand dollar?
How could I be happy without you?
除了條件狀語(yǔ)從句之外,原因狀語(yǔ)從句也會(huì)出現(xiàn)虛擬語(yǔ)氣.
o 由in order that, so that引起的從句,肯定的時(shí)候可以使用may/might; can/could; 否定的時(shí)候,多用shouldn't;
o whoever, whatever, no matter what引起的從句中,多用may+
情態(tài)動(dòng)詞的基本用法及其區(qū)別
最近幾年高考試題中常常借助語(yǔ)境來(lái)考查情態(tài)動(dòng)詞的基本用法及其區(qū)別,因此在平時(shí)學(xué)習(xí)時(shí)準(zhǔn)確理解和掌握情態(tài)動(dòng)詞的基本用法十分重要.情態(tài)動(dòng)詞的用法復(fù)雜多變,在高考試題中,命題者常常利用語(yǔ)境和句子之間意義上的細(xì)微差別來(lái)考查學(xué)生對(duì)情態(tài)動(dòng)詞的理解和掌握.對(duì)于情態(tài)動(dòng)詞,除了要求考生能夠準(zhǔn)確掌握它們的基本用法外,還要充分利用高考試題所設(shè)置的語(yǔ)境來(lái)分析句子之間所體現(xiàn)的特殊關(guān)系.下面就近幾年來(lái)高考試題中出現(xiàn)的情態(tài)動(dòng)詞的考點(diǎn)進(jìn)行歸納分析,以便同學(xué)們復(fù)習(xí)掌握.
一、用“情態(tài)動(dòng)詞＋have ＋done”結(jié)構(gòu)表示對(duì)過(guò)去動(dòng)作的推測(cè),高考試題中常用過(guò)去時(shí)態(tài)或過(guò)去的時(shí)間狀語(yǔ)給以暗示.情態(tài)動(dòng)詞的這一用法可以用 “對(duì)立統(tǒng)一”來(lái)概括.
1．當(dāng)試題的前句和后句在動(dòng)作和意義上相互補(bǔ)充說(shuō)明,且整個(gè)句意在動(dòng)作和時(shí)間上是一個(gè)整體時(shí),我們可用“統(tǒng)一”關(guān)系來(lái)解決這樣的試題.常見(jiàn)的結(jié)構(gòu)有：
must have done：
表示對(duì)過(guò)去動(dòng)作的肯定推測(cè),常譯作“一定做了……”,只能用于肯定句中.其否定形式為can’t／couldn’t have done?
疑問(wèn)式為Can／Could...have done?.
could ／might have done：表示對(duì)過(guò)去發(fā)生的動(dòng)作的可能性推測(cè),常譯作“可能做了……”.如：
1) My sister met him at the Grand Theater yesterday afternoon, so he
＿＿＿＿＿ your lecture． ?
A． couldn’t have attended
B． needn’t have attended
C． mustn’t have attended
D． shouldn’t have attended
本題選A.
2) Jack ＿＿＿＿ yet, otherwise he would have telephoned me．
A． mustn’t have arrived
B． shouldn’t have arrived
C． can’t have arrived
D． need not have arrived （C）
2．當(dāng)試題的前后句在動(dòng)作和意義上構(gòu)成轉(zhuǎn)折關(guān)系時(shí),常借助“but, however, instead”等詞來(lái)表示過(guò)去的動(dòng)作與客觀事實(shí)不符,這時(shí)我們就可以用“對(duì)立”關(guān)系來(lái)解決這樣的試題.這種結(jié)構(gòu)常見(jiàn)的有：
should have done ／ ought to have done：表示過(guò)去本應(yīng)該做某事而實(shí)際上沒(méi)有做.
should not have done ／ ought not to have done：表示過(guò)去本不應(yīng)該做某事但事實(shí)上卻做了.
need have done：表示過(guò)去本來(lái)有必要去做某事,但事實(shí)上沒(méi)有做.
need not have done：表示過(guò)去本來(lái)沒(méi)有必要做某事,但事實(shí)上卻做了.如：
3) I was really anxious about you． You ＿＿＿＿＿ home without a word．
(NMET2001)
A． mustn’t leave B． shouldn’t have left
C． couldn’t have left D． needn’t leave
“本不應(yīng)該離家出走卻走了”,故本題選B.
4) I told Sally how to get here, but perhaps I ＿＿＿＿＿ for her．
(NMET’94)
A． had to write it out
B． must have written it out
C． should have written it out
D． ought to write it out
由句中的連詞but可知前后句之間是對(duì)立關(guān)系,分析題意可知本題應(yīng)選C.
二、考查情態(tài)動(dòng)詞基本用法之間的比較和辨析.最近幾年高考試題中常借助具體的語(yǔ)境來(lái)考查考生對(duì)那些最常見(jiàn)的情態(tài)動(dòng)詞的基本用法的理解和掌握,因此在做這樣的試題時(shí)應(yīng)認(rèn)真分析語(yǔ)境中所含的實(shí)際意義,并結(jié)合情態(tài)動(dòng)詞的基本含義和用法做出正確的選擇.
5) —Is John coming by train?
—He should, but he ＿＿＿＿＿＿ not． He likes driving his car．
A． must B． can C． need D． may
mustn’t 表示“禁止、不準(zhǔn)”；cannot 表示“不可能”；need not 表示“不必要”；may not
表示“可能不”.分析語(yǔ)境可知本題應(yīng)選D.
6) —I hear you’ve got a set of valuable Australian coins． ＿＿＿＿＿＿ I have a look?
—Yes, certainly．
A． Do B． May C． Shall D． Should
分析語(yǔ)境可知這是在征求對(duì)方的許可,may表示“允許、可以”,語(yǔ)氣比較委婉? shall常用于第一、三人稱作主語(yǔ)的疑問(wèn)句中,表示征求對(duì)方意見(jiàn)和指示,如果此空用shall,則意為“要（我）看一下嗎?”,不符合上下文意思.故本題選B.
7) Mr Bush is on time for everything． How ＿＿＿＿ it be that he was late for the opening ceremony?
A． can B． should C． may D． must
must be 表示肯定的猜測(cè),只能用于肯定句中,由題意可知本題應(yīng)選A.
8) —Are you coming to Jeff’s party?
—I’m not sure． I ＿＿＿＿ go to the concert instead．
A． must B． would C． should D． might
由題意和下句中的 “I’m not sure”
可知這段對(duì)話中存在一種可能性推測(cè),might可以用來(lái)表示一種比較委婉的可能性判斷,故本題選D.又如： I should have been there, but I ＿＿＿＿＿ not find the time．
A． would B． could C． might D． should
分析題意可知第二個(gè)分句表示過(guò)去的某種能力；C 項(xiàng)只表示語(yǔ)氣上的可能性,與題意不符.故本題選B.
9) Johnny, you ＿＿＿＿ play with the knife, you ＿＿＿＿ hurt yourself．
A． won’t; can’t B． mustn’t; may
C． shouldn’t; must D． can’t; shouldn’t
mustn’t 表示“不可以；禁止”,分析題意可知第二個(gè)空表示某種可能性,故本題選B.
10) —Will you stay for lunch?
—Sorry, ＿＿＿＿＿＿． My brother is coming to see me．
A． I mustn’t B． I can’t
C． I needn’t D． I won’t
分析題意可知因?yàn)椤拔业艿芤獊?lái)看我”,所以“不能留下”,因此對(duì)別人的邀請(qǐng)或要求應(yīng)給予禮貌的拒絕.A 項(xiàng)表示“禁止”；C項(xiàng)表示“不必要”；而D項(xiàng)表示“不會(huì)”,均不符合題意.故本題選B.又如：
—Could I borrow your dictionary?
—Yes, of course you ＿＿＿＿＿．
A． might B． will C． can D． should (C)
11)—When can I come for the photos? I need them tomorrow afternoon．
—They ＿＿＿＿＿ be ready by 12?00．
A． can B． should C． might D． need
該題考查情態(tài)動(dòng)詞should的基本含義,分析句意可知本題應(yīng)選B.又如：
12) The fire spread through the hotel very quickly but everyone ＿＿＿＿ get out．(
A． had to B． would C． could D． was able to
該題考查了could和be able to的區(qū)別,二者都可表示過(guò)去時(shí)間的能力,但如果表示過(guò)去成功地做了某事只能使用was ／ were able to do,故本題選D.
13) —Shall I tell John about it ?
—No, you ＿＿＿＿＿． I’ve told him already．
A． needn’t B． wouldn’t C． mustn’t D． shouldn’t
情態(tài)動(dòng)詞shall在試題中表示征詢對(duì)方意見(jiàn)或請(qǐng)求指示.答句暗示 “沒(méi)有必要了”,故本題選A