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所跟帖: 樊弓 今日新闻高手解读 2020-09-21   2020-09-21 08:27:52  


作者: aops   Terry Tao:It ought to be common knowledge 2020-09-21 11:59:30  [点击:1463]
It ought to be common knowledge that Donald Trump is not fit for the presidency of the United States of America


In logic, there is a subtle but important distinction between the concept of mutual knowledge – information that everyone (or almost everyone) knows – and common knowledge, which is not only knowledge that (almost) everyone knows, but something that (almost) everyone knows that everyone else knows (and that everyone knows that everyone else knows that everyone else knows, and so forth). A classic example arises from Hans Christian Andersens’ fable of the Emperor’s New Clothes: the fact that the emperor in fact has no clothes is mutual knowledge, but not common knowledge, because everyone (save, eventually, for a small child) is refusing to acknowledge the emperor’s nakedness, thus perpetuating the charade that the emperor is actually wearing some incredibly expensive and special clothing that is only visible to a select few. My own personal favourite example of the distinction comes from the blue-eyed islander puzzle, discussed previously here, here and here on the blog. (By the way, I would ask that any commentary about that puzzle be directed to those blog posts, rather than to the current one.)

I believe that there is now a real-life instance of this situation in the US presidential election, regarding the following


https://terrytao.wordpress.com/2016/06/04/it-ought-to-be-common-knowledge-that-donald-trump-is-not-fit-for-the-presidency-of-the-united-states-of-america/

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