核心问题
You be joking! must 与 have (got) to 都可以表示推论(逻辑上的必然性)。请问它们在这个意义上是否还有区别?
词典解答
have（got）to 与 must 都可以用来表示推论(“必定”“一定”“准是”)。但是，have（got）to 强调从客观上推论，因此“逻辑上的必然性”的意义比 must 更强。请对比：
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He must be hungry. 他一定饿了。
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If Bley was aboard, he had to have heard me. 如果布雷在船上，他一定会听到我的喊声。
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She must be asleep (=She can't be awake). (CGEL) 她准是睡着了。
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There has (got) to be a first time for everything. (CGEL) 任何事情都必然有一个开头。
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A: I'm the worst runner in the race. There were five runners and I came fifth.
B: Don't worry. Someone had to come last.
A: 在这次赛跑中我是最糟的运动员。一共有五个运动员，而我跑了第五。
B: 不要难过。总要有人跑倒第一的。
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There had to be some solution to the problem. (CGEL) 这个问题总得有某种解决方法。
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He was standing upright, so he had to be all right. (RL, Book 3, L.2) 他挺直地站在那里，所以他一定没有发生什么事。