英語(yǔ)語(yǔ)法講解:情態(tài)動(dòng)詞(第八講)
情態(tài)動(dòng)詞與動(dòng)詞的時(shí)態(tài)和語(yǔ)態(tài)
情態(tài)動(dòng)詞又稱為情態(tài)助動(dòng)詞。英語(yǔ)中助動(dòng)詞主要有兩類：一是基本助動(dòng)詞，如have, do, be等；二是情態(tài)助動(dòng)詞，如may, must, need等。情態(tài)動(dòng)詞與其他動(dòng)詞連用表示說(shuō)話人的語(yǔ)氣，可表達(dá)建議、要求、可能、意愿等。情態(tài)動(dòng)詞沒(méi)有人稱和數(shù)的變化。
一、情態(tài)動(dòng)詞+動(dòng)詞完成式
情態(tài)動(dòng)詞must, should, may(might), ought to, can(could), need, would等都可以與動(dòng)詞完成式連用作謂語(yǔ)，其模式為“modal verb+have+v-ed”。這類結(jié)構(gòu)表示對(duì)過(guò)去所發(fā)生動(dòng)作的推測(cè)或判斷。但是，不同的情態(tài)動(dòng)詞所表示的意思又有所不同。
1、must+have+v-ed和can’t/couldn’t+have+v-ed
“must+have+v-ed”表示對(duì)過(guò)去事情較有把握的、肯定性的推測(cè)，常譯為“一定”，“準(zhǔn)是”，“肯定”。當(dāng)must用于推測(cè)意義時(shí)，其否定形式通常不是must not, 而是can/could not.“can’t/couldn’t+have+v-ed”表示對(duì)過(guò)去事情的否定性推測(cè)，常譯為“決不可能”，“不太可能”。
例：Since the ditch is full of water, it must have rained last night.
經(jīng)典練習(xí)：
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、答案選C。must have+v-ed表示推測(cè)過(guò)去某事一定發(fā)生；may have+v-ed表示推測(cè)過(guò)去某事也許發(fā)生。Should/ought to have+v-ed表示“本應(yīng)該…”根據(jù)句意，C為正確選項(xiàng)。
2、答案選D。can’t have+v-ed表示對(duì)過(guò)去發(fā)生事情的否定推測(cè)；needn’t+have+v-ed表示過(guò)去做了本不必做的事。根據(jù)句意D為正確選項(xiàng)。
3、答案選C。根據(jù)本句的后半句otherwise she would have replied before now可知，前半句是一個(gè)表示與后半句相應(yīng)的虛擬過(guò)去情況的句子。Can’t/couldn’t
have v-ed表示過(guò)去不可能發(fā)生的事情。所以C為正確選項(xiàng)。
4、答案選B。像be believed/found/known/reported/said/supposed/thought后常跟不定式完成式，表達(dá)“據(jù)知，據(jù)報(bào)道”等意思，不定式的動(dòng)作發(fā)生在被動(dòng)結(jié)構(gòu)(謂語(yǔ)動(dòng)作)所表示的動(dòng)作之前。根據(jù)語(yǔ)法要求B為正確選項(xiàng)。
