21.4 比较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。 |