在職GCT英語：情態(tài)動詞的對比解析

 　　在GCT英語考試中，語法是非常重要的知識點，在整個復(fù)習的過程當中，就可以快速的提升GCT英語考試能力。為幫助廣大GCT考生提高GCT英語考試水平，中國教育在線整理匯總了一些重要情態(tài)動詞，供參考：

　　情態(tài)動詞+ have +過去分詞

　　1) may(might) have + done sth, can (could) have + done sth　表示過去，推測過去時間里可能發(fā)生的事情。

　　Philip can (could) have been hurt seriously in the car accident.

　　2) must have +done sth，對過去時間里可能發(fā)生的事情的推測，語氣較強，具有“肯定”，“諒必”的意思。

　　—Linda has gone to work, but her bicycle is still here.

　　—She must have gone by bus.

　　3) ought to have done sth, should have done sth

　　本應(yīng)該做某事，而事實上并沒有做。否定句表示“不該做某事而做了”。

　　You ought to (should) have been more careful in this experiment.

　　He ought not to have thrown the old clothes away.(事實上已扔了。)

　　ought to 在語氣上比should 要強。

　　4) needn?t have done sth　 本沒必要做某事

　　I dressed very warmly for the trip, but I　needn?t have done so. The weather was hot.

　　5) would like to have done sth　 本打算做某事

　　I would like to have read the article, but I was very busy then.

　　比較have to和must

　　1)　兩詞都是‘必須’的意思，have to 表示客觀的需要， must 表示說話人主觀上的看法，既主觀上的必要。

　　My brother was very ill, so I had to call the doctor in the middle of the night.　我弟弟病得很厲害，我只得半夜里把醫(yī)生請來。(客觀上需要做這件事)

　　He said that they must work hard. 他說他們必須努力工作。(主觀上要做這件事)

　　2)　have to有人稱、數(shù)、時態(tài)的變化，而must只有一種形式。但must 可用于間接引語中表示過去的必要或義務(wù)。

　　He had to look after his sister yesterday.

　　3) 在否定結(jié)構(gòu)中： don?t have to　 表示“不必” ;mustn?t　表示“禁止”

　　You don?t have to tell him about it.　 你不一定要把此事告訴他。

　　You mustn?t tell him about it.　你一定不要把這件事告訴他。