2019年高考英語二輪專題復(fù)習(xí)6情態(tài)動詞和虛擬語氣
10.情態(tài)動詞+have done的用法
①could+have done：本可以做而實際上未能做
you could have done better, but you didn’t try your best.
②cannot+have done：表示對過去行為的否定推測
he cannot have been to that town.
③can+主語+have done：表示對過去行為的懷疑或不肯定
can he have got the book?
④might(may)+ have done：對過去發(fā)生的行為不太肯定的推測
he may not have finished the work.
if we had taken the other road, we might have arrived earlier.
(mood:might>may,possibility:might<may)
⑤must+have done：對過去發(fā)生的行為肯定的推測。其否定式為：cannot have done
you must have seen the film.
you cannot have seen the film.
⑥needn’t+have done：本來不必要做的而實際上又做了
you needn’t have watered the flowers,for it is going to rain.
注意：didn’t need to(have to)do :沒有必要做而實際上也沒有做
i didn’t need to clean the windows.my sister did it 2 hours ago.
⑦should(ought to)+ have done：本來應(yīng)該做而實際上又沒有做。
其否定形式表示某種行為不該發(fā)生卻發(fā)生了。
you should have started earlier, but you didn’t.
she shouldn’t have taken away my measuring tape, for i wanted to use it.
注意：本結(jié)構(gòu)還可以表“推測”的意思
he should have finished the work by now.
到現(xiàn)在他應(yīng)該已經(jīng)做完那項工作了。
11.其它情態(tài)動詞
①have to
have to表示 “必須, 不得不”, 在這個意義上與must很接近, 但must表示的是說話人的主觀看法, 而
have to表示的卻是客觀需要. have to比must有更多的形式。
the tv set is broken. i have to buy a new one.
the students will have to know how to use the computers.
注意：在回答must的問句時, 否定式常用need not(needn’t)或don’t have to表示 “不必”。而不用
must not, 因為must not表示 “不可以”。
②used to
表示過去的習(xí)慣動作或狀態(tài)(現(xiàn)在已不復(fù)如此)
—did you use to go there to see your brother? /used you to go there to see your brother?
—yes, i did(used to). /no , i didn’t (usedn’t).
注意：would也可表示過去反復(fù)發(fā)生的動作或某種傾向，但是不涉及到現(xiàn)在。
③had better
表示 “最好(做……)”
we had better go now.
其否定式為had better not
ii.虛擬語氣
（一）一般虛擬結(jié)構(gòu)
類別 用法 例句
if引導(dǎo)的條件從句 與現(xiàn)在事實相反 從句動詞：過去式（be用were）
主句動詞：should/would/could/might+動詞原形 if he were here, he would help us.
與過去事實相反 從句動詞：had+過去分詞
主句動詞：should/would/could/might+have+過去分詞 if i had been free, i would have visited you.
與將來事實相反 從句動詞：過去式 / should+動詞原形 / were+不定式