 Even if one were to reject Lederman’s skeptical argument (be it by agreeing with Immerman’s argument above, or with the argument by Thomason (2021) addressed in the next section, or otherwise), care must be taken in ascribing common knowledge to a group of human agents. Common knowledge is a phenomenon highly sensitive to the agents’ circumstances. The following section gives an example that shows that in order for \(A\) to be a common truism for a set of agents, they ordinarily must perceive an event which implies \(A\) simultaneously and publicly.