核心问题
The other students in the class keep their eyes closed. They mustn't look.
《初中英语重点·难点纵横谈》(中国科技大学出版社, p.64) 在注释中说:
“I mustn't be late. (我可不能迟到了。)不可以说: I can't be late.” 该书 p.33 也曾提到: “汉语说‘不能’, 英语不等于‘can't’, 而要说‘mustn't’。例: 你不能坐下。英语要说: You mustn't sit down. (不用 can't)”
请问真的不能说 I can't be late. You can't sit down. 吗?
词典解答
我们知道,can既可以表示“能力”或“可能”,也可以表示“被允许”,因而,can't可用于上面所有的意义。I can't be late.除表示“我不可能迟到。”之外,还可以表示“我不可以(不允许)迟到”。同样,You can't sit down.也可以表示“你不可以坐下。”请看下面的例证:
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You can't go swimming. ("You are not allowed to..." 你不许去游泳。
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Put that cigarette out! You can't smoke near a petrol pump. 把香烟熄灭了！在汽油泵旁边不许吸烟。
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You can't pick the ball up in football. 踢足球时不可以用手拿球。
由此可见，can't 与 mustn't 一样，也可表示“不允许”“不可以”“不准”等含义。