mustn't 是 must 的否定形式吗?

从形式上看, mustn't(must not)是must的否定形式,但从意义上看,它并不是作“必须”解的must的否定形式。作“必须”解的否定形式为:need not, don't need to, don't have to(不必)。

1. “Must I come at four o'clock?” “Oh no, you needn't come at four.” “我必须4点钟来吗?” “哦，不，你不必4点来。”

2. “We must stay home, mustn't we?” “Yes, you must. [No, you don't have to.]” “我们必须留在家里，是吗？”“是，你们应当留在家里。[不，你们不用。]”

mustn't(must not)的含义是:“禁止”“不允许”“不可以”“不准”:

1. You must not tell a lie. 你不许说谎。

2. You mustn't play on the road. 你们不允许在马路上玩。

3. You mustn't smoke in the classroom. 你不得在教室里吸烟。

4. We mustn't be late, must we? 我们不许迟到, 是吧?

应当牢记的是，mustn't(must not)是may的否定式，相当于may not，见may not/mustn't。

[句意]他们不许看。