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)

With closer interactions between academic and commercial entities the role of the university is expanding to also include knowledge transferIn the biomedical and health sciences , close interactions between academic and commercial entities are now common place. Funds from pharmaceutical and biotechnology companies have helped finance major bioscience projects and research centres, graduate students are receiving training in commercial laboratories, and university scientists are translating their ‘intellectual property’ by patenting their research and launching start-up companies. And this is happening (...) with the blessing of universities, who see the commercialisation of research – and the royalties brought in from ‘technology transfer’ – as part of their new mission.The result is that no longer are universities simply places of higher learning, where academics are dedicated to teaching and research, traditionally the ‘first’ and ‘second’ missions of universities; universities now have a ‘third’ mission, to engage in knowledge transfer. Governments and research-intensive industries , are keen to translate university research into marketable products. Facilitated by policies and laws to protect intellectual property rights and aid commercialisation, universities are transforming into ‘entrepreneurial’ institutions.1 University administrators seek to generate new funding streams, while governments see universities as drivers of technology development and economic growth. In such a climate, it should not be surprising that researchers in many disciplines are facing pressure to collaborate …. (shrink)

In this article, we expand the analytical and theoretical foundations of the study of knowledge commons in the context of more classical agrarian commons, such as seed commons. We show that it is possible to overcome a number of criticisms of earlier work by Ostrom (Governing the commons. The evolution of institutions for collective action, Cambridge University Press, Cambridge, 1990) on natural commons and its excludability/rivalry matrix in addressing the inclusive social practices of “commoning”, (...) defined as a way of living and acting for the preservation of the commons. Our empirical analysis emphasizes, using the most recent advances in the IAD/SES framework, the distributed and collaborative knowledge governance in a French peasant seed network as a key driver for reintroducing cultivated agrobiodiversity and on-farm seed conservation of ancient and landrace varieties. These inclusive peasant seed groups developed alternative peer-to-peer models of collaborative peasant-led community-based breeding and grassroots innovations in the search for more resilient population varieties. Our results highlight the various models of collective action within the network and discuss the organizational tradeoffs of opting out of peasant seed activities and recreating a shared collective knowledge base on the benefits of restoring cultivated agrobiodiversity. It helps us better understand how modern peasant seed groups function as epistemic communities which contributes to envisioning alternative agricultural systems. (shrink)

What is common knowledge? According to the dominant iterative model, a group of people commonly knows that p if and only if they each individually know that p, and they furthermore each know that they each know that p, and so on to infinity. According to the integrative model proposed in this paper, a group commonly knows that p when its members are united in a state of mind of the type whose contents must be true. Epistemic integration within (...) a group is enabled by symmetrical signalling processes such as eye contact. In conversational dyads, symmetrical processing operates on pairs of signals produced by the two sides in a familiar format: speakers generate content for joint attention in main channel communication, and addressees evaluate that content in backchannel communication. Processes of reinforcement learning shape our pairwise signalling, driving the accumulation of common knowledge, both in response to extrinsic reward for coordinated action, and in response to the intrinsic reward of curiosity. Where the iterative model caps the epistemic performance of the group at the level of its weakest member, the integrative model of common knowledge shows how groups working together can outperform their strongest member working alone. (shrink)

Background Relatively little information is available regarding the level of acceptance of evolution and knowledge about evolution in different educational settings in Europe. The aim of the present study is to fill this gap and provide a comprehensive overview of the current state of research regarding evolutionary knowledge and acceptance of students and teachers across Europe, based on a systematic literature review. -/- Results We identified 56 papers for the period 2010–2020, presenting results for 29 European countries. Both (...) knowledge and acceptance of evolution were assessed in 17 studies. Out of 13 instruments most commonly used in the literature, five have been used in the European context so far: ACORNS, CINS, I-SEA, KEE and MATE. Thirty-one other instruments were identified of which 16 were used in studies on knowledge and 15 in studies on acceptance. The extent of knowledge was hard to compare even within groups of the same education level due to the application of different instruments and assessment of different key concepts. Our results illustrate the persistence of misconceptions through all education levels. Comparing acceptance among different education levels and countries revealed a high diversity. However, a lack of evolution in curricula tended to be associated with rejection of evolution in some countries. European studies that investigated both acceptance of evolution and knowledge about evolution varied highly concerning the existence and strength of the relationship between these factors. However, some trends are visible, such as an increase of strength of the relationship the higher the education level. -/- Conclusions The present review highlights the lack of a standardized assessment of evolutionary knowledge and acceptance of evolution across Europe and, therefore, of reasonably comparable data. Moreover, the review revealed that only about one-third of all studies on acceptance and/or knowledge about evolution provided evidence for local validity and reliability. We suggest the use of assessment categories for both knowledge and acceptance instruments to allow for interpretation and comparison of sum scores among different sample groups. This, along with prospective comparative research based on similar samples, paves the way for future research aimed at overcoming current biases and inconsistencies in results. (shrink)

[EN]In recent decades, problems related to the accessibility and sustainability of science have increased, both in terms of the acquisition and dissemination of knowledge and its generation. Policymakers, academics, and, increasingly, citizens themselves have developed various approaches to this issue. Among them, citizen science is distinguished by making possible the generation of scientific knowledge by anyone with an interest in doing so. However, participation alone does not guarantee knowledge generation, which represents an epistemological challenge for citizen science. (...) Simultaneously, economic and socio-institutional difficulties in science governance and maintenance have grown. To solve those problems, several market elements have been introduced, a solution rejected by those who consider science as a public good that states must guarantee. Alternatively, research and work on the commons are growing worldwide, the concept being extended from natural resources to knowledge resources. In this chapter, we propose science as a commons, underlining the essential role of citizen science. Difficulties also apply to citizen science itself, but the increasing development of a multitude of projects based on cooperation favours the conditions required for its sustainability and quality. Our philosophical proposal is based on empirical knowledge about citizen science coupled with socio-economic concepts, according to a sociopolitical epistemology. (shrink)

This article presents a community-based account of salience as an alternative and a complement to the ‘natural salience’ approach which is endorsed by almost all game theorists who use this concept. While in the naturalistic approach, salience is understood as an objective and natural property of some entities, the community-based account claims that salience is a function of community membership. Building on David Lewis’s theory of common knowledge and on some of its recent refined accounts, I suggest that salience (...) acts as a correlating device in a correlated equilibrium. What is constitutive of salience is common understanding, the fact that agents have common knowledge that they share the same modes of reasoning with respect to a well-identified set of events. I argue that the basis for common understanding is community membership. The relevance of this account stems from the fact that it answers the objection that salience is either unnecessary or unable to account for coordination between rational agents. (shrink)

How is cultural progress possible? Historically, no other animal has progressed as humans have. Conventional wisdom suggests that by having language, people accumulate knowledge, which produces progress. Such Formal stage 10 wisdom begs fundamental questions. Thus, we assert the cultural necessity of levels of support, or scaffolding, for people to develop higher stages of hierarchical complexity. The resulting, wider accessibility to higher-stage action and knowledge, which requires higher stages of development to understand, enables social and scientific progress. With (...) memes and downward assimilation, larger proportions of society gain access to advanced thinking with support, in turn enabling cultural progress. (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...?".

Current dynamic epistemic logics often become cumbersome and opaque when common knowledge is added for groups of agents. Still, postconditions regarding common knowledge express the essence of what communication achieves. We present some methods that yield so-called reduction axioms for common knowledge. We investigate the expressive power of public announcement logic with relativized common knowledge, and present reduction axioms that give a detailed account of the dynamics of common knowledge in some major communication types.

Intellectual property (IP) can internalize positive externalities associated with the creation and discovery of ideas, thereby increasing investment in efforts to create and discover ideas. However, IP law also causes negative externalities. Strict IP rights raise the transaction costs associated with consuming and building on existing ideas. This causes a tragedy of the anticommons, in which valuable resources are underused and underdeveloped. By disincentivizing creative projects that build on existing ideas, IP protection, even if it increases original innovation, can inadvertently (...) reduce the rate of iterative innovation. The net effect of IP law on innovation and welfare depends on the relative magnitude of these positive and negative externalities. We argue that the current regime probably suffers from excessive, and excessively rigid, IP protection. This motivates the search for institutional alternatives and complements. We suggest that a monocentric IP rights regime may not be the only, or the most efficient, way to internalize the positive externalities of innovation. The knowledge economy supports the emergence of diverse, polycentric forms of bottom-up self-governance, both market and community led, that entail the citizen coproduction of the norms and practices of intellectual creation and discovery. (shrink)

Current dynamic epistemic logics often become cumbersome and opaque when common knowledge is added for groups of agents. Still, postconditions regarding common knowledge express the essence of what communication achieves. We present some methods that yield so-called reduction axioms for common knowledge. We investigate the expressive power of public announcement logic with relativized common knowledge, and present reduction axioms that give a detailed account of the dynamics of common knowledge in some major communication types.

The book offers a new treatment of the capacity to perceive, act on, and know about the world together with others. I argue that creatures capable of joint attention stand in a unique perceptual and epistemic relation to their surroundings: they operate in an environment that they, through their communication with their fellow perceivers, help constitute. I show that this relation can be marshaled to address a range of questions about the social aspect of the mind and its perceptual and (...) cognitive capacities. I begin with a conceptual question about a complex kind of sociocognitive phenomenon—perceptual common knowledge—and develop an empirically informed account of the spatial structure of the environment in and about which such knowledge is possible. In the course of his argument, I address such topics as demonstrative reference in communication, common knowledge about jointly perceived objects, and spatial awareness in joint perception and action. (shrink)

We sketch recent insights in dynamic epistemic logic and use them to shed new light on old ideas about common knowledge as a prerequisite for linguistic communication.

Typically, common knowledge is taken as grounds for the acceptability of a claim, while appeals to popularity are seen as fallacious attempts to support a claim. This paper poses the question of whether there is any categorical difference between appeals to common knowledge and appeals to popular opinion as argumentative moves. In answering this question, I argue that appeals to common knowledge do not, on their own, provide adequate grounds for a claim’s acceptability.

Most reductionist accounts of intentional joint action include a condition that it must be common knowledge between participants that they have certain intentions and beliefs that cause and coordinate the joint action. However, this condition has typically simply been taken for granted rather than argued for. The condition is not necessary for ensuring that participants are jointly responsible for the action in which each participates, nor for ensuring that each treats the others as partners rather than as social tools. (...) It is thus something of a mystery why the condition is so widely accepted. By rejecting three arguments that could potentially support it, I argue that reductionists should get rid of the condition. I show that two of the arguments fail. While the third argument is intuitively compelling, it builds on key premises that are unavailable to the reductionist. (shrink)

The openness of joint awareness between two or more subjects is a perceptual phenomenon. It involves a certain mutual awareness between the subjects, an awareness that makes reference to that very awareness itself. Properly characterized, such awareness can generate iterated awareness ‘x is aware that y is aware that x is aware...’ to whatever level the subjects can sustain. The openness should not be characterized in terms of Lewis–Schiffer common knowledge, the conditions for which are not met in many (...) basic cases of joint attention. A range of phenomena, including linguistic communication and other interpersonal relations, that have previously been described in terms of common knowledge should rather be seen as involving open joint awareness. An Appendix to this chapter discusses the relations of this approach to Barwise's discussions, and disputes the claim that these mental phenomena require the postulation of self-involving situations. (shrink)

This paper investigates the epistemic assumptions that David Lewis makes in his account of social conventions. In particular, I focus on the assumption that the agents have common knowledge of the convention to which they are parties. While evolutionary analyses show that the common knowledge assumption is unnecessary in certain classes of games, Lewis’ original account (and, more recently, Cubitt and Sugden’s reconstruction) stresses the importance of including it in the definition of convention. I discuss arguments pro et (...) contra to argue that, although the assumption might be relevant to a descriptively adequate account of social convention, it is not required for its rational reconstruction. I then point out that Lewis’ account, properly speaking, is of common reason to believe, rather than of common knowledge, and argue that, in order to formalize aptly the distinction between reason to believe and belief, standard formal epistemic models need to be supplemented with so-called awareness structures. Finally, I stress that the notion of knowledge implicit in Lewis’ text involves interesting elements that cannot be captured in the standard propositional formalizations, but need the full expressive force of quantified epistemic logic. (shrink)

Epistemic protocols are communication protocols aiming at transfer of knowledge in a controlled way. Typically, the preconditions or goals for protocol actions depend on the knowledge of agents, often in nested form. Informal epistemic protocol descriptions for muddy children, coordinated attack, dining cryptographers, Russian cards, secret key exchange are well known. The contribution of this paper is a formal study of a natural requirement on epistemic protocols, that the contents of the protocol can be assumed to be common (...) knowledge. By formalizing this requirement we can prove that there can be no unbiased deterministic protocol for the Russian cards problem. For purposes of our formal analysis we introduce an epistemic protocol language, and we show that its model checking problem is decidable. (shrink)

Common knowledge is ubiquitous in our lives and yet there remains considerable uncertainty about how to model or understand it. Standard analyses of common knowledge end up being challenged by either regress or circularity which then give rise to well-known paradoxes of practical reasoning, such as the Two Generals’ Paradox. This paper argues that the nature and utility of common knowledge can be illuminated by appeal to Wittgenstein’s Hinge Epistemology. It is argued that those things that we (...) standardly think of as being common knowledge in our lives are the same as those that Wittgenstein identified as hinge certainties. This identification of common knowledge with hinge certainties allows us to resolve the regress problem for common knowledge and explain how the Two Generals’ Paradox arises. (shrink)

If an autonomous rational agent can freely choose whether to get vaccinated under pandemic conditions, should he or she be held responsible for deciding not to? Let the term to be held responsible...

The paper surveys the currently available axiomatizations of common belief (CB) and common knowledge (CK) by means of modal propositional logics. (Throughout, knowledge- whether individual or common- is defined as true belief.) Section 1 introduces the formal method of axiomatization followed by epistemic logicians, especially the syntax-semantics distinction, and the notion of a soundness and completeness theorem. Section 2 explains the syntactical concepts, while briefly discussing their motivations. Two standard semantic constructions, Kripke structures and neighbourhood structures, are introduced (...) in Sections 3 and 4, respectively. It is recalled that Aumann's partitional model of CK is a particular case of a definition in terms of Kripke structures. The paper also restates the well-known fact that Kripke structures can be regarded as particular cases of neighbourhood structures. Section 3 reviews the soundness and completeness theorems proved w.r.t. the former structures by Fagin, Halpern, Moses and Vardi, as well as related results by Lismont. Section 4 reviews the corresponding theorems derived w.r.t. the latter structures by Lismont and Mongin. A general conclusion of the paper is that the axiomatization of CB does not require as strong systems of individual belief as was originally thought- only monotonicity has thusfar proved indispensable. Section 5 explains another consequence of general relevance: despite the "infinitary" nature of CB, the axiom systems of this paper admit of effective decision procedures, i.e., they are decidable in the logician's sense. (shrink)

Restricting attention to the class of extensive games defined by von Neumann and Morgenstern with the added assumption of perfect recall, we specify the information of each player at each node of the game-tree in a way which is coherent with the original information structure of the extensive form. We show that this approach provides a framework for a formal and rigorous treatment of questions of knowledge and common knowledge at every node of the tree. We construct a (...) particular information partition for each player and show that it captures the notion of maximum information in the sense that it is the finest within the class of information partitions that satisfy four natural properties. Using this notion of “maximum information” we are able to provide an alternative characterization of the meet of the information partitions. (shrink)

David Lewis is widely credited with the first formulation of common knowledge and the first rigorous analysis of convention. However, common knowledge and convention entered mainstream game theory only when they were formulated, later and independently, by other theorists. As a result, some of the most distinctive and valuable features of Lewis' game theory have been overlooked. We re-examine this theory by reconstructing key parts in a more formal way, extending it, and showing how it differs from more (...) recent game theory. In contrast to current theories of common knowledge, Lewis' theory is based on an explicit analysis of the modes of reasoning that are accessible to rational individuals and so can be used to analyse the genesis of common knowledge. Lewis' analysis of convention emphasises the role of inductive reasoning and of salience in the maintenance of conventions over time. Footnotes Earlier versions of this paper were presented at the 13th Amsterdam Colloquium at the University of Amsterdam, at a workshop on social norms at Wissenschaftskolleg zu Berlin, and at seminars at Tilburg University and the University of Bristol. We are grateful for comments from participants at those meetings, from two anonymous referees, and from Michael Bacharach, Nick Bardsley, Cristina Bicchieri, Luc Bovens, Simon Grant, David McCarthy, Shepley Orr, Brian Skyrms, Peter Vanderschraaf, Peter Wakker and Jörgen Weibull. Robert Sugden's work was supported by the Leverhulme Trust. (shrink)

Not only is the common‐law standard of proof of mere likelihood in ordinary civil cases justifiable, but its justifiability supports the conclusion that there is no general norm that one must assert that p only if p is known. An argument by Voltaire is formalized to show that the mere likelihood standard is rational. It is also shown that no applicable norm preempts the common‐law rule. An objection that takes the pertinent knowledge‐norm to be honoured in the breach is (...) rejected by appeal to the absence of blameworthiness in alleged breaches of interest. An objection that takes civil verdicts to be manifestations of acceptance, rather than assertoric, is considered and rejected. (shrink)

We develop a logical system that captures two different interpretations of what extensive games model, and we apply this to a long-standing debate in game theory between those who defend the claim that common knowledge of rationality leads to backward induction or subgame perfect (Nash) equilibria and those who reject this claim. We show that a defense of the claim à la Aumann (1995) rests on a conception of extensive game playing as a one-shot event in combination with a (...) principle of rationality that is incompatible with it, while a rejection of the claim à la Reny (1988) assumes a temporally extended, many-moment interpretation of extensive games in combination with implausible belief revision policies. In addition, the logical system provides an original inductive and implicit axiomatization of rationality in extensive games based on relations of dominance rather than the usual direct axiomatization of rationality as maximization of expected utility. (shrink)

The openness of joint awareness between two or more subjects is a perceptual phenomenon. It involves a certain mutual awareness between the subjects, an awareness that makes reference to that very awareness itself. Properly characterized, such awareness can generate iterated awareness ‘x is aware that y is aware that x is aware...’ to whatever level the subjects can sustain. The openness should not be characterized in terms of Lewis–Schiffer common knowledge, the conditions for which are not met in many (...) basic cases of joint attention. A range of phenomena, including linguistic communication and other interpersonal relations, that have previously been described in terms of common knowledge should rather be seen as involving open joint awareness. An Appendix to this chapter discusses the relations of this approach to Barwise's discussions, and disputes the claim that these mental phenomena require the postulation of self-involving situations. (shrink)

The coordinated attack scenario and the electronic mail game are two paradoxes of common knowledge. In simple mathematical models of these scenarios, the agents represented by the models can coordinate only if they have common knowledge that they will. As a result, the models predict that the agents will not coordinate in situations where it would be rational to coordinate. I argue that we should resolve this conflict between the models and facts about what it would be rational (...) to do by rejecting common knowledge assumptions implicit in the models. I focus on the assumption that the agents have common knowledge that they are rational, and provide models to show that denying this assumption suffices for a resolution of the paradoxes. I describe how my resolution of the paradoxes fits into a general story about the relationship between rationality in situations involving a single agent and rationality in situations involving many agents. (shrink)

The two of us commonly know a proposition just in case (i) we both know it, (ii) we both know that we both know it, (iii) we both know that we both know that we both know it, and so on. In a recent paper titled ‘Uncommon Knowledge’, Harvey Lederman (2018) argues against the possibility of common knowledge. His argument rests on the empirical claim that there are minor individual variations in how we perceive things. This motivates a (...) principle about perception: when two people are perceiving something and it perceptually appears a certain way to one of them, then for all that person knows, it perceptually appears a slightly different way to the other. In this paper, I challenge Lederman’s perceptual principle and thereby his argument. In particular, I argue that there are some circumstances in which things perceptually appear a certain way to me and nonetheless I know that they don’t perceptually appear in a slightly different way to you. Indeed, I argue that not only are there exceptions to the perceptual principle, but they are widespread. (shrink)

A large class of games is that of non-cooperative, extensive form games of perfect information. When the length of these games is finite, the method used to reach a solution is that of a backward induction. Working from the terminal nodes, dominated strategies are successively deleted and what remains is a unique equilibrium. Game theorists have generally assumed that the informational requirement needed to solve these games is that the players have common knowledge of rationality. This assumption, however, has (...) given rise to several problems and paradoxes. Most notably, it has been shown that the common knowledge assumption makes the theory of the game inconsistent at some information set. The present paper shows that a) no common knowledge of rationality need be assumed for the backward induction solution to hold. Rather, it is sufficient that the players have a number of levels of knowledge proportional to the length of the game, and b) it is also necessary that the number of levels of knowledge is finite and proportional to the length of the game. For a higher number of levels of knowledge, inconsistencies arise. (shrink)

An opinionated introduction to philosophical issues connected to common knowledge.

The meaning of an utterance is often enriched by the pragmatic context in which it is uttered. This is because in ordinary conversations we routinely and uncontroversially compress what we say, safe in the knowledge that those interpreting us will ‘add in’ the content we intend to communicate. Does the same thing hold true in the case of legal utterances like ‘This constitution protects the personal rights of the citizen’ or ‘the parliament shall have the power to lay and (...) collect taxes’? This article addresses this question from the perspective of the constitutional originalist—the person who holds that the meaning of a constitutional text is fixed at some historical moment. In doing so, it advances four theses. First, it argues that every originalist theory is committed to some degree of pragmatic enrichment, the debate is about how much. Second, that in determining which content gets ‘added in’, originalists typically hold to a common knowledge standard for enrichment, protestations... (shrink)

Two approaches for defining common knowledge coexist in the literature: the infinite iteration definition and the circular or fixed point one. In particular, an original modelization of the fixed point definition was proposed by Barwise in the context of a non-well-founded set theory and the infinite iteration approach has been technically analyzed within multi-modal epistemic logic using neighbourhood semantics by Lismont. This paper exhibits a relation between these two ways of modelling common knowledge which seem at first quite (...) different. (shrink)

We study the relationship between common knowledge and the sequence of iterated mutual knowledge from a topological point of view. It is shown that common knowledge is not equivalent to the limit of the sequence of iterated mutual knowledge. On that account the new epistemic operator limit knowledge is introduced and analyzed in the context of games. Indeed, an example is constructed where the behavioral implications of limit knowledge of rationality strictly refine those of (...) common knowledge of rationality. More generally, it is then shown that limit knowledge of rationality is capable of characterizing any solution concept for some appropriate epistemic-topological conditions. Finally, some perspectives of a topologically enriched epistemic framework for games are discussed. (shrink)

Can we know anything for certain? There are those who think we can (traditionally labeled the "dogmatists") and those who think we cannot (traditionally labeled the "skeptics"). The theory of knowledge, or epistemology, is the great debate between the two. This book is an introductory and historically-based survey of the debate. It sides for the most part with the skeptics. It also develops out of skepticism a third view, fallibilism or critical rationalism, which incorporates an uncompromising realism about perception, (...) science, and the nature of truth. (shrink)

We show the faithful embedding of common knowledge logic CKL into game logic GL, that is, CKL is embedded into GL and GL is a conservative extension of the fragment obtained by this embedding. Then many results in GL are available in CKL, and vice versa. For example, an epistemic consideration of Nash equilibrium for a game with pure strategies in GL is carried over to CKL. Another important application is to obtain a Gentzen-style sequent calculus formulation of CKL (...) and its cut-elimination. The faithful embedding theorem is proved for the KD4-type propositional CKL and GL, but it holds for some variants of them. (shrink)

Suppose a speaker S and an audience A are in a communication coordination problem. That is, for some proposition p, they each prefer that S mean that p and that A believe p in response. How do they coordinate their thought and action to solve the problem? The Gricean answer is that they reason their way to the solution. Pragmatics makes a similar assumption. “Pragmatics involves perception augmented by some species of ‘ampliative’ inference … a sort of reasoning”. There are (...) two objections. The first is that it is not plausible to attribute such reasoning to speakers and audiences. The second objection grants, for the sake of argument, that speakers and audiences reason in the required ways. The objection is that this is not sufficient to solve coordination problems since a speaker and an audience may not know how each has reasoned. The problem is well-known in game theory, which typically solves it by assuming the parties’ preferences are common knowledge. Common knowledge is the recursive belief state in which people are know something, know they know it, know they know they know it, ad infinitum. I propose a similar solution. When people interact as speaker and audience, common knowledge arises from their perceptions of each other as fulfilling the roles of speaker and audience. The account of how common knowledge arises entails Grice’s general characterization of conversational implicatures. More precisely, it entails speakers and audiences involved in communication coordination problems typically commonly know that a relevant instance of the conditions holds. The common knowledge approach requires attributing reasoning to speakers and audiences, but it keeps those attributions to a plausible minimum. Thus the common knowledge approach is a viable alternative to current approaches that attribute extensive reasoning to speakers and audiences.A common knowledge-based approach to pragmatics would answer at least the following question: What informative generalizations are possible about the role of contexts in generating common knowledge relevant to conversational implicatures? The question is important. “Much has been learned about these domains of psychology from a focus on the problem of altruistic cooperation and the mechanisms of reciprocity. We hope that comparable insights are waiting to be discovered by psychologists as they investigate the problem of mutualistic cooperation, and the mechanisms of common knowledge are—as we might say—put out there”. (shrink)