 In certain contexts, agents might not be able to achieve common knowledge. The skeptical argument put forth by Lederman (2018b), indeed, rests on and generalizes related arguments about the attainability of common knowledge that were made in theoretical computer science in relation to the coordinated attack problem (see Lederman 2018a, Halpern and Moses, 1990 and Fagin et al. 1995, esp. chapters 6 and 11). In the context of distributed systems, using the formal systems of epistemic logic that, as mentioned above, are equivalent to the semantic approach privileged by economists, it can be proven formally that (i) common knowledge is necessary for coordination and that (ii) the attainability of common knowledge depends on assumptions made about the system. In particular, asynchronous systems do not allow for common knowledge of a communicated message to arise, making coordination impossible. Might the agents achieve something “close” to common knowledge? There are various weakenings of the notion of common knowledge that can be of use: \(\varepsilon\)-common knowledge (agents will achieve common knowledge within time \(\varepsilon\), hence they will coordinate within time \(\varepsilon)\), eventual common knowledge (agents will achieve common knowledge and therefore coordinate eventually), probabilistic common knowledge (agents will achieve probability \(p\) common belief, and hence with probability \(p\) successfully coordinate), etc. Such weakenings of the notion of common knowledge might prove useful depending on the intended application.