四六级

　　进入暑假状态的同学们都有什么安排与计划呢？有没有为学习英语留出一些时间？尤其是语法知识相对薄弱的同学，暑假正是恶补的最好时期。从今天开始小编每天为大家整理一些英语四级语法基础知识，希望大家认真复习。

        2017年12月英语四级基础语法知识大全

　　情态动词+ have +过去分词

　　1) may(might) have + done sth, can (could) have + done sth　表示过去，推测过去时间里可能发生的事情。

　　Philip may (might) have been hurt seriously in the car accident.

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

　　2) must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"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

　　本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。

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

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

　　ought to 在语气上比should 要强。

　　4) needn't have done sth　 本没必要做某事

　　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.

　　have to和must

　　1)　两词都是'必须'的意思，have to 表示客观的需要， must 表示说话人主观上的看法，既主观上的必要。

　　My brother was very ill, so I had to call the doctor in the middle of the night.　我弟弟病得很厉害，我只得半夜里把医生请来。(客观上需要做这件事)

　　He said that they must work hard. 他说他们必须努力工作。(主观上要做这件事)

　　2)　have to有人称、数、时态的变化，而must只有一种形式。但must 可用于间接引语中表示过去的必要或义务。

　　He had to look after his sister yesterday.

　　3)　在否定结构中： 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诉他。

　　You mustn't tell him about it.　　　　你一定不要把这件事告诉他。

　　希望以上内容可以帮助到对于英语语法有困惑的同学，想了解更多四六级备考课程、备考资讯，请点击文都网校四六级资讯站查询!

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