June 11-12, 2026
University Paris-Panthéon-Assas
12, Place du Panthéon
Program Committee:
Galit Ashkenazi-Golan * Dietmar Berwanger * Olivier Bos * Michael Greinecker * Paul Égré * Ziv Hellman * Christina Katt-Pawlowitsch * Roni Katzir * Herakles Polemarchakis * Jörgen Weibull
Image: Sylvia K. Kummer
With talks by:
Scott Aaronson (University of Texas at Austin, Computer Science)
Galit Ashkenazi-Golan (London School of Economics, Mathematics)
Riccardo Bruni (University of Florence, Literature and Philosphy)
Jean-Pierre Cléro (University of Rouen, Philosophy)
Armando Cote (Psychanalyste, Paris, Centre de soins Primo Levi)
Alma Frischoff (MIT, Linguistics and Philosophy)
Yannai A. Gonczarowski (Harvard University, Economics and Computer Science)
Olga Gorelkina (UM6P, Africa Business School, Moroccan Center for Game Theory)
Olivier Gossner (CNRS, École Polytechnique, and London School of Economics)
Ani Guerdjikova (University of Grenoble Alpes, Economics)
Ziv Hellman (Bar-Ilan University, Economics)
Marilynn Johnson (University of San Diego, Philosophy)
Roni Katzir (Tel Aviv University, Computational Linguistics Lab)
David Lagziel (Ben-Gurion University of the Negev, Economics)
Jérémy Ledent (University Paris Cité, Institut de Recherche en Informatique Fondamentale)
Yoram Moses (Technion-Israel Institute of Technology, Electrical Engineering)
Aran Nayebi (Carnegie Mellon, Machine Learning and NeuroAgents lab)
Christina Pawlowitsch (Université Paris-Panthéon-Assas, Laboratoire d'Économie Mathématique et de Microéconomie Appliquée)
Steven Pinker (Harvard University, Psychology)
Miklós Pintér (Corvinus University, Economics)
Herakles Polemarchakis (University of Warwick, Economics)
Klaus Ritzberger (University of London, Royal Holloway)
Pierre Tarrès (NYU Shanghai and Courant Institute of Mathematical Sciences)
Daniel Toneian (University of Vienna, Facutly of Mathematics)
Elias Tsakas (Maastricht University, Economics)
Rafael Veiel (University of Texas at Austin, Economics)
Bernhard von Stengel (London School of Economics, Mathematics)
Jörgen Weibull (Stockholm School of Economics)
Orr Well (Tel Aviv University, Computational Linguistics Lab)
Program
12, Place du Panthéon
Salle des conseils, stairs M, 2nd floor
Wednesday, June 10, 2026
Pre-conference event: Tutorials
17h-19h:
17h: Roni Katzir: The modeling of "Questions" by information partitions in linguistics
18h: Christina Pawlowitsch Understanding the Agreement Theorem, its implicit assumptions, its interpretations. Does it describe conditions ever met in life?
9h00-10h30
Chair: Paul Égré
Herakles Polemarchakis: "On the Road to Agreement"
Yoram Moses: "What is Common About Common Knowledge?"
Yannai Gonczarowski: "Common Knowledge, Regained"
10h30-11h: Coffee break
11h-12h30
Chair: Sergio Rajsbaum
Scott Aaronson: The Complexity of Agreement, With New Directions and Applications
Aran Nayebi: "Intrinsic Barriers and Practical Pathways for Human-AI Alignment: An Agreement-Based Complexity Analysis"
Daniel Toneian: "Delta-Epsilon Common Knowledge"
12h30-14h00: Lunch break
14h-15h30
Chair: Jean-Marc Tallon
Olga Gorelkina: "Collusion via Information Sharing"
Ziv Hellman: "Charges and Bets: A General Characterisation of Common Priors"
Roni Katzir: "Focus and Questions"
15h30-16h: Coffee break
16h-17h30
Chair: Jörgen Weibull
Dov Samet: "Common Knowledge Cannot be Defined in the Object Language"
Steven Pinker: "The Mental Representation of Common Knowledge"
Open discussion
9h-10h30. Salle 3.
Chair: Keny Chatain
Orr Well: "Ineffability Follows from a Question-Based Approach to Focus"
Alma Frischoff: "A General Account of Exhaustification with an Iterated Rationality Model"
Marilynn Johnson: "Veiling with Multiple Audiences: Cooperative Communication in Speech and Fashion"
9h-10h30. Salle des Conseils.
Chair: Yossi Feinberg
Galit Ashkenazi-Golan: "The Role of Information in Adaptive Dynamics in Games"
Rafael Veiel: "Three Views on Common Knowledge of Rationality"
John Levy: "Nash Equilibrium in Games of Incomplete Information via Common Knowledge Partitions"
10h30-11h: Coffee break
11h-12h30. Salle 3
Chair:Christina Pawlowitsch
Ani Guerdjikova: "How Do You Know What I Mean? Implication and Translation"
David Lagziel: "Comparison of Oracles"
Riccardo Bruni: "Weak Epistemic Commitment and Coordination"
11h-12h30. Salle des Conseils.
Chair: Ziv Hellman
Jérémy Ledent: "Distributed Knowledge in Simplicial Models"
Bernhard von Stengel: "Social Deduction Games and Language"
Scott Duke Kominers and Jujian Zhang: "We Can't Agree to Disagree, Formally: Aumann's Theorem and Assumption Accounting in Lean"
12h30-14h: Lunch break
14h-15h30. Salle 3.
Chair: Olivier Bos
Armando Cote: "Lacan: 'Le temps logique et la certitude anticipée'"
Nadia Sigalov: "Entangled Knowledge: More Than Models, More Than Narratives"
14h-15h30. Salle des Conseils.
Chair: Michael Greinecker
Miklós Pintér: "Consistency of Beliefs: An Overview"
Elias Tsakas : "Local Epistemic Conditions in Large Games"
Olivier Gossner: "A Measurable Approach to Information Equivalence"
15h30-16h: Coffee break
16h-17h30. Salle des Conseils.
Chair: Yannick Viossat
Pierre Tarrès: "On the Dynamics in Signaling Games"
Klaus Ritzberger and Jörgen Weibull: "Reflections on Language and Sender-Receiver Games"
Rida Laraki: "What Preferences Can—and Cannot—Predict in Multi-Agent Online Learning"
Galit Ashkenazi-Golan (London School of Economics, Mathematics)
"The Role of Information in Adaptive Dynamics in Games"
We give a high-level introduction to adaptive dynamics, with emphasis on the role of information. From information about the game, to information about the opponent and information about the adaptive process the opponent is using.
Riccardo Bruni (University of Florence, Literature and Philosophy)
"Weak Epistemic Commitment and Coordination"
Based on joint work with Alessandro Gioffré
The Electronic Mail Game (EMG), introduced by Rubinstein (1989), serves as a foundational model for understanding the limits of communication in strategic interaction. By formalizing a scenario where players exchange automated messages, the EMG illustrates a profound paradox: strategic coordination cannot compensate for the strict lack of common knowledge. Despite generating high-order mutual knowledge through communication, players mathematically fail to coordinate on a payoff-dominant equilibrium, an outcome that sharply contradicts intuitive rational behavior.In this talk, we argue that existing probabilistic approximations of common knowledge, such as Monderer and Samet's (1989) p-beliefs, leave this paradox unresolved because they primarily model external communication noise rather than internal epistemic commitment. To address this, we introduce a novel epistemic framework that enriches the logical language of game theory by combining "ε-beliefs"---a threshold-based variant of subjective confidence---with a concept of "grounding". Unlike standard models that treat knowledge as a limit case of vanishing error, our framework models belief formation as a structural threshold phenomenon. We demonstrate that when players' beliefs are properly grounded in the concrete evidence available to them, the optimal strategy profile naturally emerges as an iterated ε-belief. Furthermore, under specific validity conditions, this profile solidifies into a common ε-belief. By distinguishing between the mechanics of information transmission and the internal standards of agent confidence, this framework theoretically validates the intuitive choice to coordinate. Crucially, this resolution provides a justification for coordination that relies neither on the specific payoff distribution of the game nor on the strict assumption of utility maximization, offering new pathways for modeling norms and collective action in multi-agent systems.
Jean-Pierre Cléro (University of Rouen, Philosophy)
"Éthique lacanienne et théorie des jeux"
En partant du dilemme des prisonniers, dont Lacan fait l’objet d’un article dès 1945 et dont il reprendra l’analyse par la suite, en particulier dans les Écrits (1966), nous considérerons ce que l’éthique de la psychanalyse doit à la théorie des jeux. Peut-être aussi, et de façon plus risquée de ma part, ce que cette éthique aurait pu en prélever et qui fût d’importance égale à sa réflexion sur le temps logique et sur l’assertion de certitude anticipée. L’œuvre de Harsanyi est en plein développement dans les années 50-60 ; le nom d’Harsanyi n’apparaît pas dans « L’éthique de la psychanalyse ». Toutefois son auteur a déjà rencontré le travail de Von Neumann et de Morgenstern. Mon propos est donc de tenter d’esquisser les affinités de la recherche lacanienne en matière d’éthique avec les recherches éthiques et politiques (le plus souvent anglosaxonnes) inséparables de la théorie des jeux.
Armando Cote (Psychanalyste, Paris, Centre de soins Primo Levi)
"Lacan: 'Le temps logique et la certitude anticipée'"
Grâce aux réflexions sur la théorie des jeux et le temps logique, la frontière entre l’individuel et le collectif est abolie. Le discours analytique, depuis sa naissance, a toujours été critiqué pour rester une pratique individuelle, mais en réalité, il constitue un nouveau discours qui fonde un lien social. Lacan reprend un binaire resté en suspens chez Freud, celui de l’individuel et du collectif. L’introduction d’un troisième terme était nécessaire pour tenter de comprendre ce qui fait lien entre les individus. Un terme autre que le moi (self) s’impose : le sujet. Dans la théorie analytique, le sujet est déterminé par le temps logique. Pour garantir l’existence du sujet, il faut trois Lacan insiste sur cette limite comptable pour délimiter ce qui constitue une foule et ce qui relève du collectif. La collectivité « se définit comme un groupe formé d’individus, au contraire de la généralité, qui se définit comme une classe comprenant abstraitement un nombre indéfini d’individus ». Il faut souligner un facteur propre à la collectivité et qui échappe à la logique : il s’agit de la structure temporelle, qui repose non sur ce que le sujet voit, mais sur ce qu’il ne voit pas. Le discours analytique est le seul qui prenne en compte le temps d’arrêt, c’est-à-dire la scansion suspensive. L’apport de Jacques Lacan à la théorie des jeux réside dans ce nouveau rapport à la vérité, considérée comme une assertion conclusive, qui s’impose dans un moment de hâte. Lacan pose ainsi les bases d’un nouveau rapport entre l’individuel et le social, par rapport à la course à la vérité. Pour y parvenir, « il faut le temps ».
Alma Frischoff (MIT, Linguistics and Philosophy)
"A General Account of Exhaustification with an Iterated Rationality Model"
Scalar Implicatures (SIs), such as the inference from ‘some’ to ‘some but not all’ have been extensively studied in recent decades, both theoretically and experimentally. In recent work, Fox and Katzir (2021) provide two arguments supporting a grammatical approach to SIs over a family of pragmatic, game-theoretic models referred to as Iterated Rationality Models (IRMs), based on conjunctive readings of disjunctive (CRD) sentences. First, they argue that IRMs are unable to derive CRDs with more than two disjuncts. Second, they argue that IRMs are extremely sensitive to prior probabilities in the case of CRDs, and conclude that SI computation is modular. The goal of this work is to explore what it would take to make IRMs compatible with the arguments in the literature. Our main conclusions are: (a) that the ‘naive speaker’ in IRMs needs to be rethought, adopting a notion of weighted message scores (WMS); and (b) that the IRM itself needs to be conceptualized as an exhaustivity operator rather than a pragmatic process, to deal with modularity issues. These are nontrivial departures from familiar views on IRMs, but they are warranted by the empirical arguments. This sharpens a challenge for current semantic/pragmatic theories: choosing between competing exhaustivity mechanisms.
Yannai A. Gonczarowski (Harvard University, Economics and Computer Science)
"Common Knowledge, Regained"
For common knowledge to arise in dynamic settings, all players must simultaneously come to know it has arisen. Consequently, common knowledge cannot arise in many realistic settings with timing frictions. This counterintuitive observation of Halpern and Moses (1990) was discussed by Arrow et al. (1987) and Aumann (1989), was called a paradox by Morris (2014), and has evaded satisfactory resolution for four decades. We resolve this paradox by proposing a new definition for common knowledge, which coincides with the traditional one in static settings but is more permissive in dynamic settings. Under our definition, common knowledge can arise without simultaneity, particularly in canonical examples of the Haplern-Moses paradox. We demonstrate its usefulness by deriving for it an agreement theorem à la Aumann (1976), showing it arises in the setting of Geanakoplos and Polemarchakis (1982) with timing frictions added, and applying it to characterize equilibrium behavior in a dynamic coordination game.
Olga Gorelkina (UM6P, Africa Business School, Moroccan Center for Game Theory)
"Collusion via Information Sharing"
This paper studies collusion via certified sharing of information in the context of mechanism design with transfers. The model of collusion builds on Aumann’s (1976) description of knowledge. A cartel can agree on a contract to collude if it is common knowledge within the cartel that the contract is incentive compatible and individually rational. Subsequently, robustness of mechanisms to collusion via information sharing is defined as the impossibility of an agreement to collude. Robust mechanisms are characterized in three settings with variable degrees of agents' liability to the cartel. Finally, I introduce a novel collusion-robust auction mechanism that achieves the second-best revenue.
Olivier Gossner (CNRS, École Polytechnique, and London School of Economics)
"A Measurable Approach to Information Equivalence"
Following Harsanyi (1967/68), an information environment in a Bayesian game can be represented by a probability space equipped with players’ information σ-fields and a measurable map to the state of nature. Since these primitives are probabilistic and measurable, it is natural to ask which aspects of an information environment are intrinsically measurable, and which aspects enter only because one introduces a topology for technical convenience.
Ani Guerdjikova (University of Grenoble Alpes, Economics)
"How Do You Know What I Mean? Implication and Translation"
When agents entertain distinct perceptions of the word, communication between them will be imprecise. In particular, under differential awareness, an event as described by one agent may find no exact analog in another agent’s subjective understanding. Within this context, it is natural to consider a syntactic model where the agent’s understanding of the world is embodied by a language (i.e., a set of interconnected descriptions of the world). Communication between agents can therefore be understood as a process of translating statements from one language to another. This paper asks how such a translation might arise and how it might be identified by an observer. We show that even if translation between languages is consistent, i.e., preserves logical implications, it need not imply the existence of a joint state-space that embeds the individual models of the two agents. We expose why this failure occurs and provide an axiom that ensures the existence of a joint state space which embeds the individual state-spaces.
Ziv Hellman (Bar-Ilan University, Economics)
"Charges and Bets: a General Characterization of Common Priors"
We show that the equivalence of common priors and absence of agreeable bets of the famous no-betting theorem can be generalized to any infinite space (not only compact spaces) if we expand the set of priors to include probability charges as priors. Going beyond the strict prior/no common prior dichotomy, we further uncover a fine-grained decomposition of the class of type spaces into a continuum of subclasses in each of which an epistemic condition approximating common priors is equivalent to a behavioral condition limiting acceptable bets.
Marilynn Johnson (University of San Diego, Philosophy)
"Veiling with Multiple Audiences: Cooperative Communication in Speech and Fashion"
In his 2007 book The Stuff of Thought and later papers in 2008, 2010, and 2011 Steven Pinker considers the work of philosopher of language Paul Grice and proposes a number of instances of perceived non-cooperation as problem cases for Grice’s Cooperative Principle. Pinker proposes a game-theoretic framework to understand some cases of what he calls “veiled speech” that, according to his argument, cannot be accounted for by Grice. I will begin by explaining what Pinker gets wrong about Grice’s Cooperative Principle, which is well equipped to explain the types of cases Pinker proposes as problematic, drawing on my previous work (Johnson 2016). We can understand some forms of so-called “veiled speech” as instances of a speaker cooperating with multiple audiences, which Grice discusses. When a speaker produces an utterance she may do so with two (or more) different hearers in mind, and aim to optimize with these both. Finally, I will connect this discussion with recent work in philosophy of fashion (Johnson 2022; Simmenauer and Ramponi Forthcoming) to consider how we might apply these ideas of cooperation with multiple audiences to the choices we make when adorning the body. Depending on whose gaze we are under there may be different costs and benefits to the messages sent with our clothing, and we as rational bodies moving in the world make choices such as wearing ambiguous clothing (Simmenauer and Ramponi, forthcoming), removing clothing, completely changing, and sometimes literally veiling to optimize these payoffs.
Roni Katzir (Tel Aviv University, Computational Linguistics Lab)
"Focus and Questions"
Focus dependencies, including question-answer congruence (QF), free focus (FF), and association with focus (AF), are often treated in terms of various grammatical mechanisms that rely on (a) focus-semantic values along a second semantic dimension, and (b) an anaphoric operator, ~, that is sensitive to these values and can communicate them to various processes. I argue against this view and in favor of a unification through a pragmatic condition: an utterance is felicitous only if it is a good answer to a good (explicit or accommodated) question, with relevance understood relative to a question-induced partition of the context set.
Scott Duke Kominers (Harvard Buisiness School) and Jujian Zhang (Axiom Math):
"We Can't Agree to Disagree, Formally: Aumann's Theorem and Assumption Accounting in Lean"
Article
David Lagziel (Ben-Gurion University of the Negev, Economics)
"Comparison of Oracles"
To what extent can an information provider influence the public's joint perception? We examine how far a public information provider, such as a media outlet, platform, or institutional mediator, can shape the way a group collectively understands the world when individuals already possess private information. Our analysis identifies fundamental constraints on the set of shared beliefs that can arise from public signals, showing that not every collective perception is achievable, even with carefully designed communication. Informational structure alone can impose subtle and sometimes surprising limits on how beliefs can be shifted, and these limits may prevent smooth or gradual changes in public opinion. We also develop a framework for comparing different information providers in terms of their ability to influence strategic outcomes, emphasizing the role of shared understanding and higher order beliefs in shaping collective behavior. Overall, the results clarify both the power and the inherent limits of public information in influencing joint perception in strategic environments.
Rida Laraki (UM6P, Moroccan Center for Game Theory)
"What Preferences Can—and Cannot—Predict in Multi-Agent Online Learning"
We examine the interplay between ordinal, preference-based solution concepts in games and the outcomes of payoff-driven learning dynamics, asking to what extent the combinatorial data of a game—its preference graph—can predict the long-run behavior of no-regret dynamics such as follow-the-regularized-leader (FTRL). In one direction, we show that the skeleton of every dynamically stable set (i.e., the set of pure profiles it contains) must also be preferentially stable, that is, it must be closed under profitable deviations. We then ask the converse question: when are preferences sufficient to describe the long-run behavior of the players’ learning dynamics? We begin by showing that preferences are indeed enough to fully characterize asymptotic stability in the case of subgames—i.e., subsets of pure profiles obtained by restricting players’ action sets. Beyond this case however, the equivalence between dynamic and preferential stability breaks down: in particular, we construct a three-player game with a preferentially stable set whose span is dynamically unstable, showing that preferences are not sufficient to describe dynamically stable behavior in general. To restore stability, we introduce the notion of leaklessness, a measure of aggregate payoff drift away from a set of pure profiles, and we use it to identify a payoff-based condition guaranteeing that the span of a set of pure profiles is stable and attracting.
Jérémy Ledent (University Paris Cité, Institut de Recherche en Informatique Fondamentale)
"Distributed Knowledge in Simplicial Models"
Based on joint work with Éric Goubault and Sergio Rajsbaum
The usual semantics of multi-agent epistemic logic is based on Kripke models, which represent agents' knowledge in terms of possible worlds connected by indistinguishability relations. In this talk, I will present an alternative semantics based on simplicial complexes, a geometric structure from the field of combinatorial topology. Conceptually, this represents a shift in perspective: the fundamental object of interest is no longer the possible worlds, but the agents' points of view about the world. This reveals a geometric structure that is already implicit in the usual Kripke framework. After a brief introduction to simplicial complexes, I will focus on the notion of distributed knowledge: that is, the knowledge that a group of agents would acquire, if they were able to perfectly share their local information. As it turns out, distributed knowledge (as well as its infinite iteration, common distributed knowledge), admits a natural geometric interpretation in terms of higher-dimensional connectivity of the simplicial complex. I illustrate the approach with examples from distributed computing, in particular the majority consensus task. https://www.arxiv.org/abs/2602.06945
John Levy (University of Glasgow, Adam Smith Business School)
"Nash Equilibrium in Games of Incomplete Information via Common Knowledge Partitions"
For more than four decades, a central problem in game theory has been establishing the existence of Nash equilibrium - the foundational solution concept - in Bayesian games, that is, games with incomplete information. Non-existence can arise, in particular, when the underlying knowledge structure decomposes into a continuum of self-contained components, each common knowledge among its members and each admitting an equilibrium, yet incapable of being assembled into a mathematically coherent global equilibrium. We survey these phenomena and their connections to paradoxical constructions, tracing the development of the equilibrium existence and non-existence literature over the past twenty-five years and highlighting several recent results that remain under development.
Yoram Moses (Technion - Israel Institute of Technology)
"What is Common About Common Knowledge?"
The talk will survey how Aumann's Agreeing to Disagree paper affected work on knowledge in distributed systems, and will argue that infinite nesting is not the essential aspect of common knowledge.
Aran Nayebi (Carnegie Mellon, Machine Learning, NeuroAgents lab)
"Intrinsic Barriers and Practical Pathways for Human-AI Alignment: An Agreement-Based Complexity Analysis"
We formalize AI alignment as a multi-objective optimization problem called (M, N, ε, δ)-agreement, in which a set of N agents (including humans) must reach approximate ε-agreement across M candidate objectives, with probability at least 1-δ. Analyzing communication complexity, we prove an information-theoretic lower bound showing that once either M or N is large enough, no amount of computational power or rationality can avoid intrinsic alignment overheads. This establishes rigorous limits to alignment itself, not merely to particular methods, clarifying a “No-Free-Lunch” principle: encoding “all human values” is inherently intractable and must be managed through consensus-driven reduction or prioritization of objectives. Complementing this impossibility result, we construct explicit algorithms as achievability certificates for alignment under both unbounded and bounded rationality with noisy communication. Even in these best-case regimes, our bounded-agent and sampling analysis shows that with large task spaces (D) and finite samples, reward hacking is globally inevitable: rare high-loss states are systematically under-covered, implying scalable oversight must target safety-critical slices rather than uniform coverage. Together, these results identify fundamental complexity barriers—tasks (M), agents (N), and state-space size (D)—and offer principles for more scalable human-AI collaboration.
Steven Pinker (Harvard University, Psychology)
"The Mental Representation of Common Knowledge"
Ever since the concept of common knowledge was proposed, it has been obvious that an infinite series of “I know that she knows that I know…” propositions cannot fit into a finite brain, and that whatever sense of common knowledge mortal human beings possess must take the form of a finite representation. I examine the major proposals, and present the results of studies suggesting that people represent common knowledge by a simple intuition that some fact is public, salient, self-evident, or “out there,” together with a sense that this is sufficient to spin out an unlimited number of nested propositions if they ever needed to. I discuss examples of how this interplay between self-evidence and recursive mentalizing might play out in real-world phenomena thought to be driven by common knowledge.
Miklós Pintér (Corvinus University, Economics)
"Consistency of Beliefs: An Overview"
We provide a concise overview of the literature, beginning with Aumann (1976) on the consistency of beliefs and the characterization of a common prior, and progressing to the most recent results in this area. The presentation is organized along two complementary dimensions. The first emphasizes the underlying economic and conceptual intuitions behind the results, while the second addresses the corresponding technical framework and methodological contributions.
Herakles Polemarchakis (University of Warwick, Economics)
"On the Road to Agreement"
A Bayesian dialogue is a sequential exchange of beliefs. It is the prototype of a rational dialogue. At each stage, one of two interlocutors states his beliefs formed after the revision prompted by the beliefs stated by the other at the previous stage. The dialogue terminates when nothing is left to be said. The only property of a rational dialogue is eventual agreement. A third party, with access only to the transcript of a dialogue, cannot distinguish a Bayesian dialogue from an arbitrary sequence of alternating utterances. One can consider common knowledge and agreement as equilibrium conditions and the dialog that leads to common knowledge as the adjustment path. It follows that, across fundamentals, rationality is a refutable claim at equilibrium, while, along the adjustment path, it is not. Which bears an analogy with competitive markets. While Walrasian tâtonnement that leads to equilibrium, if it does, is arbitrary, equilibrium prices and quantities are not arbitrary. They may even identify fundamentals.
Klaus Ritzberger (Royal Holloway, University of London) and
Jörgen Weibull (Stockholm School of Economics)
"Reflections on Language and Sender-Receiver Games"
We provide a game-theoretic analysis of sender-receiver games in order to shed further light on the emergence and stability of communication and language. We consider several game-theoretic approaches to this fundamental but complex issue. In particular, we use the notion of "game blocks and solid outcomes" (Ritzberger and Weibull 2025) and “tenable strategy blocks and settled equilibria” (Myerson and Weibull 2015), as well as point- and set-valued notions of evolutionary stability. In addition, we develop a novel approach to group selection that requires evolutionary stability at the individual level within groups.
Nadine (Nadia) Sigalov (Independent Scholar)
"Entangled Knowledge: More Than Models, More Than Narratives"
This talk proposes an account of knowledge exchange grounded in an entangled epistemology that brings literary studies and science into reciprocal dialogue and extends this approach to game theory, where formal models are considered alongside situated, lived experience in literature. Drawing on Kenneth Burke’s concept of the terministic screen, disciplines are approached as partial perspectives that shape what can be known and how it can be articulated across fields. Building on New Materialist frameworks associated with Karen Barad and interdisciplinary epistemology in the work of Kristin Zeiler, knowledge is understood as emerging through intra-action, a co-constitutive process in which meaning is not transferred between domains but produced through their entanglement. Synaesthesia, a neurological condition in which stimulation in one sensory or cognitive domain elicits a concurrent experience in another, serves as a heuristic model for cross-disciplinary knowledge. Literature provides the methodological space in which this model is enacted through embodied, lived experience, introducing sensory, affective, and interpretive dimensions that exceed formal description and are not reducible to paraphrase. It does not simply represent scientific accounts of synaesthesia but participates in their formation, enabling a two-way exchange between lived experience and scientific discourse rather than a hierarchical relation. Applied to game theory, this framework highlights how formal reasoning relies on simplified models of cognition and behaviour. These models privilege a formalised, logical register of reasoning, foregrounding consistency and strategic structure. In Burkean terms, they function as terministic screens that direct attention toward certain patterns while deflecting others. Following Ariel Rubinstein, economic models can be understood as “fables,” that is, formally rigorous yet deliberately stylised constructions that offer a perspective rather than a neutral account of reality. Rubinstein’s engagement with Anton Chekhov brings into view another kind of story, a literary one, that can illuminate aspects of human behaviour that formal models do not capture. An entangled, cross-disciplinary approach foregrounds literature’s capacity to render situated, lived experience, introducing forms of insight that complement and expand the scope of formal modelling.
Daniel Toneian (University of Vienna, Faculty of Mathematics)
"Delta-Epsilon Common Knowledge"
Based on joint work with Stefan Schrott and Christina Pawlowitsch
We propose a novel notion of approximate common knowledge of an event, (δ, ε)-common knowledge, which, in continuation of work by Nielsen (1984), is formulated in the language of σ-algebras and applicable for general probability spaces. For (δ, ε)-common knowledge of an event, we establish: (1) equivalence of the σ-algebra-based definition and two hierarchical definitions (generalizing Aumann’s argument showing the equivalence of the partition-based definition and the informal alternating hierarchical definition of common knowledge), and (2) a generalization of Aumann’s Agreement Theorem, showing that when two individuals have (δ, ε)-common knowledge of their posteriors of an event then the distance between these posteriors is bounded as a function of δ and ε. Furthermore, we extend Nielsen’s notion of common knowledge of a random variable to a notion of (δ, ε)-common knowledge of a random variable, formulated in terms of conditional variances. In this setting, we establish: (1) equivalence of the σ-algebra-based definition and two hierarchical definitions of (δ, ε)-common knowledge of a random variable, as well as (2) an agreement theorem for (δ, ε)-common knowledge of a random variable, showing that if the posteriors of a random variable X are (δ, ε)-common knowledge on an event B, then the L2-distance between the posteriors on B is bounded as a function of δ and ε.
Elias Tsakas (Maastricht University, Economics)
"Local Epistemic Conditions in Large Games"
The epistemic program has focused on providing foundations for game theoretic solutions concepts. This is typically done by means of conditions, like for instance common prior, common belief of rationality, etc. And while in small games such conditions seem innocent, in games with a large number of players they are more difficult to justify. Instead, it is more appealing to impose such conditions only locally in the context of an underlying network structure, e.g., it is much more reasonable to assume that players believe that their neighbors are rational, as opposed to believing in the rationality of other players who are located in very remote parts of the network. This gives rise to the following question: Can we still justify the predictions of "global" solution concepts by means of "local" epistemic conditions? In this talk I will review some of my work from the early 2010's, as well as more recent work by other authors on this question.
Rafael Veiel (UT Austin, Economics)
"Three Views on Common Knowledge of Rationality"
We will look at the different structures of information that are obtained when assuming common knowledge of rationality in a game: This endows information with 1) an algebraic structure (players information is canonically given by a additive noise), 2) a geometric structure when that noise is small and players play a global game, and finally 3) a topological structure which ensures rationalizable outcomes to be close when information is perturbed. We will survey all three.
Bernhard von Stengel (London School of Economics, Mathematics)
"Social Deduction Games and Language"
One way to extend game theory to larger and more realistic models of interaction is to use computer simulations of agents. These have long been studied as multi-agent systems in computer science, recently boosted with the apparent power of Large Language Models (LLMs). We study a known social deduction game, where players have hidden roles as belonging to two competing teams. They communicate and act to advance the winning chances of their team, where deception can be useful. The game, called "Temple of Terror", has limited messages (not necessarily truthful declarations of own cards), and actions count more than words. We programmed different machine-learning agents: One uses extensive games and learns behavior strategies with counter-factual regret, using a triple of neural networks based on a recent architecture called ESCHER. Others are prompt-engineered LLMs with different reasoning capabilities. These agents were trained in repeated play against each other, and can also play against humans using a web interface as a computer game. Of conceptual interest for game theory are team games with the concept of team-maxmin equilibrium, and signaling games where the situation is not that of cheap talk because messages can be potentially verified as truth-telling versus lying. We thus see social deduction games as a fruitful research topic for game theory and language. Joint work with Francisco Aristi-Reina and Steffen Issleib.
Orr Well (University of Tel Aviv, Computational Linguistics Lab)
"Ineffability Follows from a Question-Based Approach to Focus"
Based on joint work with Moshe Bar-Lev and Roni Katzir
Focus, typically realized through pitch accent, is known to play an important role in establishing congruence between a question and its answer. The felicity of a question- answer pair often depends on where focus is placed: (1) What does John eat in PARIS?
a. John eats CREPES in Paris.
b. # John eats crepes in PARIS.
However, Schwarzschild (1993, 1997, 2004) observes that certain seemingly harmless question-answer pairs are infelicitous, regardless of focus placement: (2) What does John only eat in PARIS?
a. # John only eats CREPES in Paris.
b. # John only eats crepes in PARIS.
(2.a) carries the unwanted inference that John eats nothing but crepes in Paris, while (2.b) triggers the improper presupposition that John eats crepes somewhere. Previous approaches to the ineffability of (2) attempt to reduce the problem to formal constraints on the structure of the answer when considered in isolation. We show that such constraints are not only stipulative, but also fail to predict that the answer can be ameliorated by modifying the preceding question or other contextual factors. We argue instead that focus ineffability arises from an interaction between semantic content and the pragmatics of question answering. Specifically, ineffability follows under the assumption that focus introduces an implicit question into discourse. In cases like (2), either the implicit question does not coherently relate to the explicit background question, or the answer itself does not appropriately address it, regardless of how focus is assigned or how only’s quantificational domain is determined. Overall, the work highlights the central role that questions and answers play in the dynamics of discourse.