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全国公共英语考试语法—haveto和must

2008-11-24 
haveto和must。
  比较haveto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.
)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。
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