Common Knowledge

The intelligence cycle is a set of processes used to provide useful information for decision-making. The cycle consists of several processes. The related counter-intelligence area is tasked with preventing information efforts from others. A basic model of the process of collecting and analyzing information is called the "intelligence cycle". This model can be applied, and, like all the basic models, it does not reflect the fullness of real-world operations. Through intelligence cycle activities, information is collected and assembled, raw information is (...) transformed into processed information, analyzed and made available to users. DOI: 10.13140/RG.2.2.25665.81760. (shrink)

The detection of hate speech and fake news in political discourse is at the same time a crucial necessity for democratic societies and a challenge for several areas of study. However, most of the studies have focused on what is explicitly stated: false article information, language that expresses hatred, derogatory expressions. This paper argues that the explicit dimension of manipulation is only one – and the least problematic – of the risks of political discourse. The language of the unsaid is (...) much more dangerous and incomparably more difficult to detect, hidden in different types of fallacies and inappropriate uses of emotive language. Through a threefold coding scheme based on the instruments of argumentation theory and pragmatics, a corpus of argumentative tweets published by 4 politicians (Matteo Salvini, Donald Trump, Jair Bolsonaro, and Joseph Biden) within 6 months from their taking office (corresponding to the official end of their election campaign) is analyzed, detecting the types of argument, the fallacies, and the uses and misuses of “emotive words.” This coding results in the argumentation profiles of the speakers, which are compared statistically to show their different implicit strategies and deceptive tactics. (shrink)

What is the relation between joint attention and common knowledge? On the one hand, the relation seems tight: the easiest and most reliable way of knowing something in common with another is for you and that other to be attentively aware of what you are together experiencing. On the other hand, they couldn’t seem further apart: joint attention is a mere perceptual phenomena that infants are capable of engaging in from nine months of age, whereas common knowledge is a cognitive (...) phenomenon involving (so it seems) complex, overlapping metarepresentational states that require the kind of sophisticated mindreading skills that developmental psychology has shown to be beyond the capabilities of young children. In 'The Shared World: Perceptual Common Knowledge, Demonstrative Communication, and Shared Social Space', Axel Seemann attempts, inter alia, to makensense of this conundrum. (shrink)

For over a decade now epistemologists have been thinking about the peer disagreement problem of whether a person is reasonable in not lowering her confidence in her belief P when she comes to accept that she has an epistemic peer on P who disbelieves P. However, epistemologists have overlooked a key realistic way how epistemic peers can, or even have to, differ epistemically—a way that reveals the inadequacy of both conformist and non-conformist views on peer disagreement by uncovering how the (...) causes of peer disagreement bear on the debate’s core philosophical issue. Part of our argument for this thesis will involve giving a thorough yet entirely informal presentation of mathematical theorems in economics by Robert Aumann :1236–1239,1976) and Polemarchakis and Geneakoplos which represent a formally precise description of how two rational agents must deal with disagreement under certain epistemically interesting circumstances. (shrink)

We study shared intentions in what we call “loose groups”. These are groups that lack a codified organizational structure, and where the communication channels between group members are either unreliable or not completely open. We start by formulating two desiderata for shared intentions in such groups. We then argue that no existing account meets these two desiderata, because they assume either too strong or too weak an epistemic condition, that is, a condition on what the group members know and believe (...) about what the others intend, know, and believe. We propose an alternative, pooled knowledge, and argue that it allows formulating conditions on shared intentions that meet the two desiderata. (shrink)

According to we-mode accounts of collective intentionality, an experience is a "we-experience"—that is, part of a jointly attentional episode—in virtue of the way or mode in which the content of the experience is given to the subject of experience. These accounts are supposed to explain how a we-experience can have the phenomenal character of being given to the subject "as ours" rather than merely "as my experience" (Zahavi 2015), and do so in a relatively conceptually and cognitively undemanding way. Galotti (...) and Frith (2013) and Schmitz (2017) present we-mode accounts that are supposed to, in particular, avoid the need for the subjects of experience to have common knowledge of each other’s perceptual beliefs. In this paper, drawing in part on Schutz’s (1932/1967; 1953) writings on "the pure We-relationship", I argue that appeal to a we-mode does not render common knowledge unnecessary. To explain when we-experiences are veridical, we-mode accounts must (i) explain how a we-experience can enable rational interpersonal coordination in some high-risk situations and (ii) explain why what is experienced is "out in the open" between the subjects of the we-experience. To do this, proponents of we-mode accounts need an account of common knowledge. In addition, they must explain why certain inferences hold between we-mode and I-mode attitudes. In light of this, we-mode accounts fare no better than content accounts in illuminating how basic forms of collective intentionality are possible. (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)

An opinionated introduction to philosophical issues connected to common knowledge.

Ordinary common knowledge is formally expressed by strong probabilistic common belief. How strong exactly? The question can be answered by drawing from the similar equivalence, recently explored, between plain and probabilistic individual beliefs. I argue that such a move entails that common knowledge displays a double fragility: as a description of a collective state and as a phenomenon, because it can respectively disappear as group size increases, or more worryingly as the epistemic context changes. I argue that despite this latter (...) fragility, the effects of common knowledge on action are robust. Unfortunately, this in turn leads to a third fragility, that of the concept of common knowledge, which threatens to collapse on probabilistic common belief. This also reveals a disanalogy between the individual and the collective cases. I finally pinpoint the subtle difference entailed by the two concepts, expressed in terms of the attitude towards contrary evidence or of the agents’ awareness. As a result, common knowledge can be defended as a concept, which refers to a fragile yet distinct collective attitude. (shrink)

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)

Robert Aumann presents his Agreement Theorem as the key conditional: “if two people have the same priors and their posteriors for an event A are common knowledge, then these posteriors are equal” (Aumann, 1976, p. 1236). This paper focuses on four assumptions which are used in Aumann’s proof but are not explicit in the key conditional: (1) that agents commonly know, of some prior μ, that it is the common prior; (2) that agents commonly know that each of them updates (...) on the prior by conditionalization; (3) that agents commonly know that if an agent knows a proposition, she knows that she knows that proposition (the “K K” principle); (4) that agents commonly know that they each update only on true propositions. It is shown that natural weakenings of any one of these strong assumptions can lead to countermodels to Aumann’s key conditional. Examples are given in which agents who have a common prior and commonly know what probability they each assign to a proposition nevertheless assign that proposition unequal probabilities. To alter Aumann’s famous slogan: people can “agree to disagree”, even if they share a common prior. The epistemological significance of these examples is presented in terms of their role in a defense of the Uniqueness Thesis: If an agent whose total evidence is E is fully rational in taking doxastic attitude D to P, then necessarily, any subject with total evidence E who takes a different attitude to P is less than fully rational. (shrink)

Standard models in epistemic game theory make strong assumptions about agents’ knowledge of their own beliefs. Agents are typically assumed to be introspectively omniscient: if an agent believes an event with probability p, she is certain that she believes it with probability p. This paper investigates the extent to which this assumption can be relaxed while preserving some standard epistemic results. Geanakoplos (1989) claims to provide an Agreement Theorem using the “truth” axiom, together with the property of balancedness, a significant (...) relaxation of introspective omniscience. I provide an example which shows that Geanakoplos’s statement is incorrect. I then introduce a new property, local balancedness, which allows us both to correct Geanakoplos’s result, and to extend it to cases where the truth axiom may fail. I exploit this general Agreement Theorem to provide novel epistemic conditions for correlated and Nash equilibrium, both of which relax the assumption of introspective omniscience. In all three cases, the results are also extended to infinite state spaces. (This is Chapter 5 of my 2014 Oxford DPhil (PhD) thesis.). (shrink)

This paper offers a comparison of three different kinds of collective attitudes: aggregate, common, and corporate attitudes. They differ not only in their relationship to individual attitudes—e.g., whether they are “reducible” to individual attitudes—but also in the roles they play in relation to the collectives to which they are ascribed. The failure to distinguish them can lead to confusion, in informal talk as well as in the social sciences. So, the paper’s message is an appeal for disambiguation.

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Over the last three decades, joint action has received various definitions, which for all their differences share many features. However, they cannot fit some perplexing cases of weak joint action, such as demonstrations, where agents rely on distinct epistemic sources, and as a result, have no first-hand knowledge about each other. I argue that one major reason why the definition of such collective actions is akin to the classical ones is that it crucially relies on the concept of common knowledge. (...) To this end, I first argue for the necessity of common knowledge for joint action in general due to the increased reliability of success it entails. I then defend the relevance of common knowledge against several criticisms, point at an adequate weakening, and discuss alternative approaches. Although structurally weaker, the common knowledge has a richer content in weak joint actions. As a result, even if the links between individuals are seriously stretched, much is still shared among them. Weak joint actions still require considerable cognitive abilities indeed. (shrink)

This paper discusses there is no sustainable theoretical alternative for building knowledge without principles including cooperation –aimed at the preparation and distribution of beliefs– among individuals. This principle helps to conceive both the relation among internalist and externalist theories, and a cognitive explanation based on the concept of epistemic warrant. The concluding remark is that concepts, like evidence or reliability, can only be conceived as skills of subjects belonging to a community.

This article discusses the current epistemological status of the political blogosphere, in light both of the concerns raised by Alvin Goldman in his 2008 paper ?The Social Epistemology of Blogging? and the recent drastic changes in the structure of the blogosphere. I argue that the political blogosphere replicates epistemically beneficial functions of the mainstream media for the functioning of democracy, and defend this claim from objections to the blogosphere that have been levelled by Goldman and Richard Posner. I then provide (...) an expanded defence of the political blogosphere in response to these particular objections. (shrink)

Defined and formalized several decades ago, widely used in philosophy and game theory, the concept of common knowledge is still considered as problematic, although not always for the right reasons. I suggest that the epistemic status of a group of human agents in a state of common knowledge has not been thoroughly analyzed. In particular, every existing account of common knowledge, whether formal or not, is either too strong to fit cognitively limited individuals, or too weak to adequately describe their (...) state. I provide a realistic definition of common knowledge, based on a formalization of David Lewis’ seminal account and show that it is formally equivalent to probabilistic common belief. This leads to a philosophical analysis of common knowledge which answers several common criticisms and sheds light on its nature. (shrink)

Mutual perceptual knowledge is a prevalent feature of our everyday lives, yet appears to be exceptionally difficult to characterise in an acceptable way. This paper argues for a renewed understanding of Stephen Schiffer’s iterative approach to mutual knowledge, according to which mutual knowledge requires an infinite number of overlapping, embedded mental states. It is argued that the charge of ‘psychological implausibility’ that normally accompanies discussion of this approach can be offset by identifying mutual knowledge, not with the infinite iterations themselves, (...) but with the finite base which Schiffer proves is capable of generating those iterations. An understanding of this finite base as a primitive, relational property holding between two or more people, allows us to understand the iterations as an implicit and ‘harmless’ intrapersonal feature of what is an interpersonal phenomenon. The paper concludes by relating the account to joint attention in infant interaction. (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)

Despite amendments to the sexual assault provisions in the Criminal Code, decisions about the availability and operation of the defence of belief in consent remain vulnerable to the influence of legally extraneous considerations. The author proposes an approach designed to limit the influence of such considerations.

Since Lewis’s (1969) and Aumann’s (1976) pioneering contributions, the concepts of common knowledge and common belief have been discussed extensively in the literature, both syntactically and semantically1. At the individual level the difference between knowledge and belief is usually identified with the presence or absence of the Truth Axiom ( iA → A), which is interpreted as ”if individual i believes that A, then A is true”. In such a case the individual is often said to know that A (thus (...) it is possible for an individual to believe a false proposition but she cannot know a false proposition). Going to the interpersonal level, the literature then distinguishes between common knowledge and common belief on the basis of whether or not the Truth Axiom is postulated at the individual level. However, while at the individual level the Truth Axiom captures merely a relationship between the individuals’ beliefs and the external world, at the interpersonal level it has very strong implications. For example, the following is a consequence of the Truth Axiom: i jA → iA, that is, if individual i believes that individual j believes that A, then individual i herself believes that A. Thus, in contrast to other axioms, the Truth Axiom does not merely reflect individual agents’ “logic of belief”. (The reason why the Truth Axiom is much stronger in an interpersonal context than appears at first glance is that it amounts to assuming that agreement of any individual’s belief with the truth is common knowledge). Given its logical force, it is not surprising to find that it has strong implications for the logic of common knowledge. In particular, if each individual’s beliefs satisfy the strongest logic of knowledge (namely S5 or KT5), the associated common knowledge operator satisfies this logic too. Such is not the case for belief: bereft of the Truth Axiom, even the strongest logic for individual belief (KD45) is insufficient to ensure the satisfaction of the “Negative Introspection” axiom for common belief: ¬ ∗A → ∗¬ ∗A (where ∗ denotes the common belief operator).. (shrink)

The project of a 'naive physics' has been the subject of attention in recent years above all in the artificial intelligence field, in connection with work on common-sense reasoning, perceptual representation and robotics. The idea of a theory of the common-sense world is however much older than this, having its roots not least in the work of phenomenologists and Gestalt psychologists such as K hler, Husserl, Schapp and Gibson. This paper seeks to show how contemporary naive physicists can profit from (...) a knowledge of these historical roots of their discipline, which are shown to imply above alla critique of the set-theory-based models of reality typically presupposed by contemporary work in common-sense ontology [1]. (shrink)