must/have to:
① 表示必须、必要,在回答问句时,如果是否定的,必须用needn’t, don’t have to
eg. ---- Must I finish my homework before dinner?
---- Yes, you must.
---- No, you don’t have to / you needn’t.
② must是说话人的主观看法, 而have to则强调客观需要,have可根据时态人称的变化而变化
eg.That film is interesting,I really must go to watch.
You have to get to school before 8 am.
③ 表示推测、可能性(只用于肯定的陈述句)
eg.You must know that,you are a teacher.
dare/need:
① dare作情态动词用时, 常用于疑问句、否定句和条件从句中
eg.How dare you say that to me?
② need 作情态动词用时, 常用于疑问句、否定句
eg. Need I finish my homework before dinner?
③ dare和 need也可以做实义动词来用,独自充当谓语。
eg.The little girl dares to go to school by herself.
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