2010年12月大學(xué)英語四六級考試必備語法精要

　　13. 表示猜測的幾種不同的方法及意義

　　一些情態(tài)動詞與動詞的完成式連用能夠表示對過去情況的猜測或者未實現(xiàn)的可能性。

　　1) could have + 過去分詞

　　A. 表示對過去可能發(fā)生的事情的推測，意為，“可能做了某事”。

　　He couldn’t have seen her yesterday.

　　They could have lost their way.

　　B. 表示某事在過去本有可能發(fā)生，但事實上并未發(fā)生，意為，“本可以做某事”。

　　We could have started a little earlier.

　　I could have killed her. It was a narrow escape.

　　2) may (might) have + 過去分詞

　　A. 表示對過去情況的推測，意為，“可能已做某事”。

　　He may have heard the news.

　　I might have come to a wrong conclusion.

　　B. 表示一種未實現(xiàn)的可能性，即本可以做某事，而實際上并沒有做，有時含有抱怨的口吻。

　　It was a narrow escape. You might have killed yourself.

　　A lot of men died who might have been saved.

　　3) must have + 過去分詞

　　表示邏輯上的必然性，即按照某些現(xiàn)象推斷過去肯定發(fā)生過的某事。

　　She must have made a big mistake.

　　The city at one time must have been prosperous, for it enjoyed a high level of civilization.

　　4) needn’t have + 過去分詞

　　表示過去不必做某事，但已經(jīng)做了，即本可不必做某事。

　　You needn’t have woken me up. I don’t have to go to work today.

　　He needn’t have watered the flowers, for it is going to rain.

　　5) should / ought to have + 過去分詞

　　表示過去應(yīng)該做某事而實際上沒有做。

　　You should / ought to have done what your parents told you. (But you failed to do it.)

　　You should / ought to have been more careful. (But you weren’t.)

　　6) shouldn’t / oughtn’t to have + 過去分詞

　　表示過去不應(yīng)該做某事而實際上卻做了。

　　You shouldn’t / oughtn’t to have crossed the road when the lights were red. (But you did.)

　　They shouldn’t / oughtn’t to have left so soon. (But they did.)

　　7) would have + 過去分詞

　　表示對現(xiàn)在或?qū)�來某時之前業(yè)已完成的動作的推測�？勺g為，“可能”、“也許”、“想必”。

　　He would have arrived by now.

　　She would have recovered by then.