Some arguments against the assumption that ordinary people may share common knowledge are sound. The apparent cost of such arguments is the rejection of scientific theories that appeal to common knowledge. My proposal is to accept the arguments without rejecting the theories. On my proposal, common knowledge is shared by ideally rational people, who are not just mathematically simple versions of ordinary people. They are qualitatively different from us, and theorizing about them does not lead to predictions about our behavior. (...) Nevertheless, models of action that assume common knowledge have a role to play in our understanding of collective rationality. (shrink)

For as long as there have been theories about common knowledge, they have been exposed to a certain amount of skepticism. Recent more sophisticated arguments question whether agents can acquire common attitudes and whether they are needed in social reasoning. I argue that this skepticism arises from assumptions about practical reasoning that, considered in themselves, are at worst implausible and at best controversial. A proper approach to the acquisition of attitudes and their deployment in decision making leaves room for common (...) attitudes. Postulating them is no worse off than similar idealizations that are usefully made in logic and economics. (shrink)

This article argues that such large-scale cases of crowd behavior as the Mexican Wave ( La Ola) constitute forms of shared intentionality which cannot be explained solely with the use of the standard intentionalistic ontology. It claims that such unique forms of collective intentionality require a hybrid explanatory lens in which an account of shared goals, intentions, and other propositional attitudes is combined with an account of the motor psychology of collective agents. The paper describes in detail the intentionalistic ontology (...) of La Ola and discusses the conditions of cooperation it meets. The discussion allows the author to defend the view that large-scale collective intentionality can be based on automaticity to a significant degree: to properly understand such phenomena like La Ola, the idea of probabilistically interpreted decisions and propensities to act should give way to the automatic aspects of behavior. This paves the way for future studies in the philosophy of action to fully recognize the role of automatic performances at the level of collective actions just as they do for individual actions. (shrink)

David Lewis is widely regarded as the philosopher who introduced the concept of common knowledge. His account of common knowledge differs greatly from most later accounts in philosophy and economy, with the central notion of his theory being ‘having reason to believe’ rather than ‘knowledge’. Unfortunately, Lewis’s account is rather informal, and the argument has a few gaps. This paper assesses two major attempts to formalise Lewis’s account and argues that these formalisations are missing a crucial aspect of this account. (...) Therefore, a new reconstruction is proposed, which explicitly discusses ‘reasons’ and uses a logic inspired by justification logic. (shrink)

One does not simply predict where the other will go, which is wherever the first predicts the second to predict the first to go, and so ad infinitum. Not "What would I do if I were she?" but "What would I do if I were she wondering what she would do if she were wondering what I would do if I were she...?".