We revisit a recent puzzle about common knowledge, the ``sailboat" case (Lederman, 2018), and argue that Lewisian common knowledge allows us to reconcile the pre-theoretical intuition that certain facts are ``public" in such situations, while these facts cannot be common knowledge in the classical, iterative sense. The crux of the argument is to understand Lewisian common knowledge as an account of what it means for an event to be public. We first formulate this argument informally to clarify its philosophical commitment and then propose one way to capture it formally in epistemic-plausibility models. Taken together, we take the philosophical and the formal arguments as providing evidence that Lewisian common knowledge is a plausible account of what it means for an event to be public.

翻译：我们重新审视了近期关于共同知识的一个谜题，即“帆船”案例（Lederman，2018），并论证刘易斯式共同知识能够调和以下直觉：某些事实在此类情境中具有“公共性”，而这些事实在经典的迭代意义上无法成为共同知识。论证的关键在于将刘易斯式共同知识理解为事件具有公共性意义的解释框架。我们首先以非形式化方式阐述该论证，以厘清其哲学承诺，随后提出一种在认知-可能性模型中形式化捕捉该论证的途径。综合而言，我们认为哲学论证与形式化论证共同表明，刘易斯式共同知识是对事件公共性含义的合理解释。