# LogiCIC Seminar

**LogiCIC Seminar**

**Between January 2012 and December 2016, we organized a monthly LogiCIC seminar series within the framework of the ERC project on "The Logical Structure of Correlated Information Change", directed by S. Smets. Every month, this seminar has hosted one or two invited speakers who presented their latest research results on topics in Logic, Epistemology and Philosophy of Science. **

**DECEMBER 6th, 2016, LogiCIC-LIRa Seminar**

Speaker: **Alexandru Baltag** (ILLC, Amsterdam)

Date and Time: Friday, December 16th 2016, 15:30-17:00

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title:** Knowing the Answer.**

Abstract: What does it mean to “know the answer” to a question? What is the relationship between this form of knowledge and the usual propositional “knowledge that” operator? Can we know the answer without knowing the question? Can we know the answer without knowing that it is the answer to this question?

I investigate logics(s) for knowing/learning answers to questions, and argue that all knowledge can in fact be reduced to this kind: at a first approximation, *to know is know how to answer a question*. Moreover, if questions (and answers) are properly construed, then knowledge, from an abstract point of view, is just a correlation between two questions (where the answer to the first carries information about the answer to the second). By reflection, agents can themselves come to know such correlations.

In this sense, *to know is to know how to use questions to answer other questions*.

**DECEMBER 2nd, 2016, LogiCIC-LIRa Seminar**

Speaker: **Johan van Benthem** (ILLC & Stanford)

Date and Time: Friday, December 2nd 2016, 15:00-16:10

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Decidable Versions of First-Order Predicate Logic.**

Abstract: There are two roads to decidability in first-order logic: one restricts attention to language fragments, or one generalizes the usual semantics. I will discuss a recent semantics by Aldo Antonelli, which gives a decidable version of predicate logic with an effective translation into the Guarded Fragment. I compare this with existing decidable semantics via general assignment models, with logics of generalized quantifiers, and with the move from relational semantics to neighborhood semantics. Open problems are flagged throughout.

**NOVEMBER 25th, 2016, Scientific symposium on****Logic, Language and Information.**

The Full day scientific programme* *hosts four invited speakers including:

Speaker:** Patrick Blackburn **(Roskilde University)

Date and Time: November 25th 2016, 13:30 – 14:15.

Venue: Lecture Hall at Tabacco Theater, NES nr 75-87, 1012 KD Amsterdam

Title: **Arthur Prior and 'Now'**

Abstract. On the 4th of December 1967, Hans Kamp sent his UCLA seminar notes on the logic of ‘now’ to Arthur Prior. Kamp’s two-dimensional analysis of 'now' led Prior to an intense burst of creativity in which he sought to integrate Kamp’s work into an orthodox one-dimensional framework. Prior's search led him through the philosophy of Castañeda, and back to his earlier work on hybrid logic; the first made temporal reference philosophically respectable, the second made it technically feasible.

Prior's six-week quest offers a fascinating glimpse into the early history of tense logic. By drawing on material from the Prior archive in the Bodleian library, and the paper “ ‘Now’” that detailed Prior's findings, I'll retell the story from a contemporary perspective. The story I'll tell is the result of joint work with Klaus Frovin Jørgensen.

Speaker:** Keith Devlin** (Stanford University)

Date and Time: November 25th 2016, 16:30 – 17:30.

Venue: Venue: Lecture Hall at Tabacco Theater, NES nr 75-87, 1012 KD Amsterdam

Title: **Taking logic into the workplace — where it rolls up its sleeves and does some useful (but dirty) work**

Abstract.* *Attempts in the 1980s and 90s at Stanford and elsewhere to apply concepts and methods of logic to study language, human communication, and real-world reasoning met with only limited success, at least in terms of their original aims. What did come out of those efforts were applications of ideas ad methods from logic in several domains, among them education, manufacturing process design, systems design, business planning, intelligence analysis, and defense technologies. In each case, those efforts met with success, when measured in terms of outcomes of significance within the domain.

**NOVEMBER 17-19, 2016, 5th LogiCIC Final Project Workshop: The Logical Structure of Correlated Information Change**

More information: logicicworkshop2016.wordpress.com.

**NOVEMBER 11th, 2016, LogiCIC-LIRa Seminar**

Speaker: **Fernando R. Velázquez Quesada**

Date and Time: Friday, November 11th 2016, 15:30-17:00

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Reliability-based preference change: lexicographic upgrade**.

Abstract: This work studies a particular method through which individuals might change their preferences according not only to what one another prefers, but also to a reliability ordering each one of them assigns to the group. More precisely, we consider agents that have not only a preference ordering over a set of objects, but also a reliability ordering over the agents themselves; then we study the effects of the public and simultaneous announcement of these individual preferences by defining an operation, the lexicographic upgrade, which receives a collection of preference relations plus a ‘priority’ ordering among them, and returns a preference relation. We will review alternative definitions of this lexicographic upgrade, depending on the properties of the priority ordering, and present a sound and complete axiom system for a language describing this operation’s effects. Time permitting, we will also discuss the effects of the iterative application of this upgrade, focusing in particular on the cases in which preference unanimity can be reached.

**OCTOBER 14th, 2016, LogiCIC-LIRa Seminar**

Speakers:** Malvin Gattinger and Hans van Ditmarsch**

Date and Time: Friday, October 14th 2016, 15:00 – 17:30.

Venue: KdVI Seminar Room F3.20, Science Park 107.

Titles: '**Knowing Values and Public Inspection' and 'Epistemic Gossip Protocols'.**

First Speaker: Malvin Gattinger (ILLC, Amsterdam)

Title: Knowing Values and Public Inspection.

Abstract. We present a basic dynamic epistemic logic of “knowing the value”. Analogous to public announcement in standard DEL, we study “public inspection”, a new dynamic operator which updates the agents’ knowledge about the values of constants. We provide a sound and strongly complete axiomatization for the single and multi-agent case, making use of the well-known Amstrong axioms for dependencies in databases.

This is joint work with Jan van Eijck and Yanjing Wang.

The paper is available at https://arxiv.org/abs/1609.03338.

Second Speaker: Hans van Ditmarsch (LORIA, Vandoeuvre-lès-Nancy)

Title: Epistemic Gossip Protocols.

Abstract. A well-studied phenomenon in network theory since the 1970s are optimal schedules to distribute information by one-to-one communication between nodes. One can take these communicative actions to be telephone calls, and protocols to spread information this way are known as gossip protocols or epidemic protocols. Statistical approaches to gossip have taken a large flight since then, witness for example the survey “Epidemic Information Dissemination in Distributed Systems” by Eugster et al. (IEEE Computer, 2004). It is typical to assume a global scheduler who executes a possibly non-deterministic or randomized protocol. A departure from this methodology is to investigate epistemic gossip protocols, where an agent (node) will call another agent not because it is so instructed by a scheduler, or at random, but based on its knowledge or ignorance of the distribution of secrets over the network and of other agents’ knowledge or ignorance of that.Such protocols are distributed and do not need a central scheduler. This comes at a cost: they may take longer to terminate than non-epistemic, globally scheduled, protocols. A number of works have appeared over the past years or are in progress (Apt et al., Attamah et al.,van Ditmarsch et al., van Eijck et al., Herzig & Maffre) of which we present a survey, including open problems yet to be solved by the community.

**SEPTEMBER 19th, 2016, LogiCIC-LIRa Seminar**

Speaker: **Branden Fitelson**

Date and Time: Monday, September 19th 2016, 11:00 – 12:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Two New(ish) Triviality Results for Indicative Conditionals.**

Abstract. I will do two things in this talk: (1) present an axiomatic generalization of Gibbard’s (logical) triviality result for indicative conditionals, and (2) present an algebraic strengthening of Lewis’s (probabilistic) triviality result for indicative conditionals. Both results start from a very weak background theory (either logical or probabilistic) of the indicative conditional, and (relative to these weak backgrounds) both results will rely only on the so-called Import-Export Law. So, these results can be viewed as (general, and strong) “odd consequences” of Import-Export.

**LIRa/LogiCIC Lecture Series with Eric Pacuit**

June 1st - June 15th 2016

Eric Pacuit (University of Maryland) will give a LIRa/LogiCIC Lecture Series between June 1st and June 15th 2016 on Neighborhood Semantics for Modal Logic. Everyone is welcome to attend the lectures. Students in the Master of Logic can subscribe to the lecture series and take part in the exercise sessions for a June Project. For more details and the full schedule, see the MSc Logic website.

**MAY 13th, 2016, LogiCIC-LIRa Seminar**

Speaker:** Guido Bacciagaluppi**

Date and Time: Friday, May 13th 2016, 13:00 – 14:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Von Neumann’s no-Hidden-Variables Theorem (and Hermann’s Critique).**

Abstract. There has been some recent debate about what von Neumann intended with his famous no-hidden-variables theorem (from his 1932 book), and on whether Bell’s now equally famous criticism is really fair to von Neumann. I revisit von Neumann’s result, which was originally published in 1927 in a paper trying to give what one would now call a “reconstruction” of quantum mechanics, and suggest a more nuanced reading. I pay special attention also to the critique of von Neumann provided by Grete Hermann in her 1935 essay on the foundations of quantum mechanics (and in an unpublished manuscript from 1933).

**APRIL 29th, 2016, LogiCIC-LIRa Seminar**

Speaker:** Rohit Parikh**

Date and Time: Friday, April 22nd 2016, 13:00 – 14:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Influencing behavior by influencing beliefs.**

Abstract. Agents act on the basis of their preferences and their beliefs. These include beliefs both about the world and about the actions of other agents.

By influencing the beliefs of agents we can also influence what choices they make. The influence need not involve deception but may simply involve withholding or offering certain truths.

We show that for a finite set of agents who know nothing about some proposition, an arbitrary state of information can be achieved by sending an n-tuple of signals, one to each agent. We consider how this will influence the actions of cautious (risk averse) or aggressive (risk loving) agents.

We next consider the case of a candidate campaigning for election who seeks the approval of voters. What sorts of things can she say to increase their approval? And is it possible to increase approval while, at the same time losing votes? We show that it is always possible to increase net approval but that this can result in losing votes.

**APRIL 22nd, 2016, LogiCIC-LIRa Seminar**

Speaker:** Rohit Parikh**

Date and Time: Friday, April 22nd 2016, 16:00 – 17:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **An Epistemic Generalization of Rationalizability.**

Abstract. Savage showed us how to infer an agent’s subjective probabilities and utilities from the bets which the agent accepts or rejects. But in a game theoretic situation an agent’s beliefs are not just about the world but also about the probable actions of other agents which will depend on their, beliefs and utilities. Moreover, it is unlikely that agents know the precise subjective probabilities or cardinal utilities of other agents. An agent is more likely to know something about the preferences of other agents and something about their beliefs. In view of this, the agent is unlikely to to have a precise best action which we can predict, but is more likely to have a set of “not so good” actions which the agent will not perform.

Ann may know that Bob prefers chocolate to vanilla to strawberry. She is unlikely to know whether Bob will prefer vanilla ice cream or a 50-50 chance of chocolate and strawberry. So Ann’s actions and her beliefs need to be understood in the presence of such partial ignorance. We propose a theory which will let us decide when Ann is being irrational, based on our partial knowledge of her beliefs and preferences, and assuming that Ann is, rational, how to infer her beliefs and preferences from her actions.

Our principal tool is a generalization of rational behavior in the context of ordinal utilities and partial knowledge of the game which the agents are playing.

**APRIL 22nd, 2016, LogiCIC-LIRa Seminar**

Speaker:** Jon Williamson**

Date and Time: Friday, April 22nd 2016, 13:00 – 14:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Inductive Logic for Automated Decision Making.**

Abstract. According to Bayesian decision theory, one’s acts should maximise expected utility. To calculate expected utility one needs not only the utility of each act in each possible scenario but also the probabilities of the various scenarios. It is the job of an inductive logic to determine these probabilities, given the evidence to hand. The most natural inductive logic, classical inductive logic, attributable to Wittgenstein, was dismissed by Carnap due to its apparent inability to capture the phenomenon of learning from experience. I argue that Carnap was too hasty to dismiss this logic: classical inductive logic can be rehabilitated, and the problem of learning from experience overcome, by appealing to the principles of objective Bayesianism. I then discuss the practical question of how to calculate the required probabilities and show that the machinery of probabilistic networks can be fruitfully applied here. This culminates in an objective Bayesian decision theory that has a realistic prospect of automation.

**APRIL 15th, 2016, LogiCIC-LIRa Seminar**

Speaker:** Jeffrey M. Keisler**

Date and Time: Friday, April 15th 2016, 13:00 – 14:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Observing, reporting and deciding in networks of agents.**

Abstract. We define an observation network as a network of agents who each have a vocabulary, a knowledge base in first-order logic, and a set of potential observations. Agents can make inferences and report them to other agents to whom they are linked, but communication is restricted to the common vocabulary of the reporter and recipient. Agents add to their knowledge bases by making observations, receiving reports from other agents, and making inferences, and share useful statements with other agents who have different vocabularies.

A well-known result from mathematical logic, the Craig Interpolation Theorem, can be interpreted in terms of knowledge sharing between pairs of agents. It is a starting point for our formal results. Certain agents called deciders are faced with alternative statements, and must decide which one is true. We consider various questions about when the network is rich enough to ensure that decisions can be made successfully if the knowledge to do so exists somewhere in the network. We obtain some easily checked completeness conditions that ensure that this is so.

The focus of the presentation will be on explanation, interpretation and application of the framework and results, rather than on their derivation. Observation networks are general enough to model many situations. We conclude by considering the example of junction tree algorithms for solving Bayes nets.

Joint work with H. Jerome Keisler, University of Wisconsin.

Biography. Jeffrey Keisler is currently Visiting Professor and Fulbright Distinguished Chair in the Mathematics and Systems Analysis Department at Aalto University in Helsinki. A Professor of Management Information Systems at the University of Massachusetts Boston, he has two books and over fifty journal articles and book chapters in decision analysis and related fields. Professor Keisler is past-President of the INFORMS Decision Analysis Society and has received its Publication Award. His PhD in Decision Sciences is from Harvard University. He will present joint work with H. Jerome Keisler who has been a leader of mathematical logic for over fifty years.

**APRIL 8th, 2016, LogiCIC-LIRa Seminar**

Speaker:** Elias Tsakas**

Date and Time: Friday, April 8th 2016, 13:00 – 14:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Reasonable Doubt Revisited.**

Abstract. According to the common definition, the standard of reasonable doubt is a threshold such that, the defendant is convicted if and only if the probability that the juror attaches to the defendant being guilty is above this threshold. In this paper we prove that generically such a threshold exists if and only if the juror reasons only about the defendant’s guilt and nothing else. We discuss the implications of this result, and subsequently we propose a weakening of the aforementioned definition, by substituting the standard of reasonable doubt with a pair of standards, an upper and a lower one, thus obtaining a sufficient condition for conviction and a sufficient condition for acquittal. Finally, we prove that the lower standard always exists, whereas the upper standard exists if and only if the juror prefers to always convict a guilty defendant, irrespective of the circumstances.

See also http://www.elias-tsakas.com/Research/Papers/ReasonableDoubt.pdf.

**MARCH 22nd, 2016**,**LogiCIC-LIRa event, Workshop****“Logical Dynamics of Social Influence and Information Change”**

Oudemanhuispoort 4-6, C1.23

Amsterdam, The Netherlands

from 14:00 to 18:00

The Workshop “Logical Dynamics of Social Influence and Information Change” will address a number of new developments in which formal methods are used to model phenomena that play a central role in epistemic-social contexts. In particular we focus on modeling agents’ epistemic and doxastic attitudes, the change of such attitudes as well as their communication-based interactions.

The following two themes will receive special attention: The first theme refers to the concept of social influence. In this context we use logic to model the spread of opinions, the exchange of information and the distribution of behavior in a social network. The second theme refers to the logical mechanism of information change as triggered by events, such as e.g. observations, communication as well as steps of logical inference.

The workshop is associated with the PhD defence of Zoé Christoff.

For more information, see https://ldsiic.wordpress.com/.

**FEBRUARY 12th 2016, LogiCIC-LIRa Seminar**

Speaker:** Rahim Ramezanian**

Date and Time: Friday, February 12th 2016, 13:00 – 14:30.

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title: **Epistemic Protocols for Dynamic Gossip.**

Abstract. A gossip protocol is a procedure for spreading secrets among a group of agents, using a connection graph. In each call between a pair of connected agents, the two agents share all the secrets they have learnt. In dynamic gossip problems, dynamic connection graphs are enabled by permitting agents to spread as well the phone numbers of other agents they know. This talk characterizes different distributed epistemic protocols in terms of the (largest) class of graphs where each protocol is successful, i.e. where the protocol necessarily ends up with all agents knowing all secrets.

**JANUARY 21th 2016, LogiCIC-LIRa Seminar**

Speaker: **Theo Kuipers (University of Groningen)**

Date and Time: Thursday, January 21st 2016, 16:00-17:30

Venue: Science Park 107, Room F1.15

Title: **Concretizations of two-sided nomic truth approximation: quantification, refinement, and stratification.**

Abstract. In a recent paper, entitled “Models, postulates, and generalized nomic truth approximation” (Synthese, open access, online DOI 10.1007/s11229-015-0916-9) I have shown that nomic truth approximation can perfectly be achieved by combining two prima facieopposing views on theories:

The traditional view: theories are sets of (models satisfying) postulates that exclude certain possibilities from being realizable.

The model view: theories are sets of models that claim to represent certain realizable possibilities, at least approximately.

From this combined perspective, nomic truth approximation, in the sense of increasing truth-content and decreasing falsity-content, can be reconstructed as a matter of revising theories by revising their models (M-side) and/or their postulates (P-side) in the face of increasing evidence.

My pre-2012 work on truth approximation, notably Kuipers (2000), was restricted to maximal theories, that is, theories in which the models are just all structures satisfying the postulates. Hence, the present two-sided approach is a far-reaching generalization. It even leaves room for two extremes: pure theories of postulates and pure theories of models.

The recent paper is based on the simplest assumptions about the further nature of theories and their claims. Starting from this ‘basic’ version I want to examine in the present paper three perspectives for concretization, 1) a quantitative/probabilistic version, 2) a refined version based on an underlying ternary similarity relation between possibilities (notably, structurelikeness between structures), 3) astratified version based on a (theory-relative) distinction between an observational and a theoretical level.

Kuipers, T., (2000), From Instrumentalism to Constructive Realism, Springer, Dordrecht, 2000.

**DECEMBER 17th 2015, LogiCIC-LIRa Seminar**

Speaker: **Allard Tamminga **

Title: **Collective obligations: logical and game-theoretic considerations.**

Date: Thursday December 17th 2015

Time: **16:00 - 17:30**

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

Abstract: I present two things: (1) a deontic logic of collective action that models collective actions, abilities, obligations, and their interrelations and (2) a game-theoretic study of the relation between what I call member obligations and individual obligations. My deontic logic of collective action shows that collective obligations and individual obligations do not match: the fulfillment of a collective obligation is neither necessary nor sufficient for the fulfillment of individual obligations. To rectify the situation, I introduce the notion of a member obligation, which is what an individual group member ought to do to help ensure that the group fulfills its collective obligation. Member obligations follow from a group plan designed to fulfill the group’s collective obligation: by highlighting particular group actions, a group plan specifies the individual actions that are the components of these highlighted group actions. Using game-theoretic means, I give structural conditions on group plans under which member obligations and individual obligations coincide.

**DECEMBER 10th 2015, LogiCIC-LIRa Seminar**

Speakers: **Jan Sprenger**

Title:**Foundations for a Theory of Causal Strength.**

Date: Thursday 10 December 2015, 16:00 - 17:30

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

Abstract. Since more than 2,500 years, there has been research on the qualitative concept of causation (“Is X a cause of Y?”). The quantitative concept (“How strong is the causal link between X and Y?”) is much less understood. In this talk, I will provide axiomatic foundations for a probabilistic logic of causal strength. Then I will connect the results to measures of effect size in statistical inference and apply them to a recent case study in Dutch tort law.

**NOVEMBER 26-28, 2015, 4th LogiCIC Workshop “Reasoning in social context”**

More information at logicicworkshop2015.wordpress.com.

**NOVEMBER 5th 2015, LogiCIC-LIRa Seminar**

Speakers: **Teddy Seidenfeld**

Title:** ****A modest proposal to use Rates of Incoherence as a guide for personal uncertainties about logic and mathematics.**

Date: Thursday 5 November 2015, 16:00 - 17:30

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

Based on joint work with Mark Schervish and Joseph Kadane.

Abstract and outline of the session. It is an old and familiar challenge to normative theories of personal probability that they do not make room for non-trivial uncertainties about (the non-controversial parts of) logic and mathematics. Savage (1967) gives a frank presentation of the problem, noting that his own (1954) classic theory of rational preference serves as a poster-child for the challenge.

First is a review of the challenge.

Second, I comment on two approaches that try to solve the challenge by making surgical adjustments to the canonical theory of coherent personal probability. One approach relaxes the Total Evidence Condition: see Good (1971). The other relaxes the closure conditions on a measure space: see Gaifman (2004). Hacking (1967) incorporates both approaches.

Third, I summarize an account of rates of incoherence; explain how to model uncertainties about logical and mathematical questions with rates of incoherence; and outline how to use this approach in order to guide the uncertain agent in the use of, e.g., familiar, numerical Monte Carlo methods in order to improve her/his credal state about such questions.

The presentation is based on the recent paper: SSK, What kind of uncertainty is that? The Journal of Philosophy, 2012.

**SEPTEMBER 10th, 2015**,**LogiCIC-LIRa event, Workshop****From Modal and Non-Classical Logics to the Mathematics of Quantum Information Flow**

Speakers:**Robert Goldblatt, Johan van Benthem, John Harding, Nick Bezhanishvili, Mingsheng Ying, Shengyang Zhong**

Date: 10th September 2015, 10:00 - 18:00

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

The aim of this workshop is to create a forum to present new developments, exchange ideas, explore and establish new connections

between logic, mathematics, computer science and physics.

Topics include the following list but are not restricted to: modal logic, non-classical logic, spatial logic, mathematical structures in logic, quantum computation and quantum information, the foundations of quantum theory.

This workshop is associated with the PhD defense of Shengyang Zhong.

For more information, see https://workshop20150910.wordpress.com/.

**MAY 28th 2015, LogiCIC-LIRa Seminar**

Speakers: **Olivier Roy, Eric Pacuit, Branden Fitelson**

Title: **LIRa/LogiCIC mini workshop on Logic and Epistemology**

Date: Thursday 28 May 2015, 13:00 - 18:30

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

On Thursday we will have a workshop on Logic and Epistemology with three guest speakers, namely Branden Fitelson, Eric Pacuit and Olivier Roy, and Alexandru Baltag.

**Programme**:

13:00 – 14:10 Eric Pacuit: Belief dynamics for interactive epistemology

14:10 – 14:30 coffee break

14:30 – 15:40 Olivier Roy: Introspection, Normality, Agglomeration

15:40 – 16:50 Branden Fitelson: Two Approaches to Belief Revision

17:00 – 18:10 Alexandru Baltag: A topological approach to belief, evidence, knowledge and learning

Afterwards we will have drinks in the ILLC common room.

**APRIL 10th 2015, LogiCIC-LIRa Seminar**

Speaker: **Davide Grossi**

Title: **Spreading Gossip Epistemically**

Date: Friday 10 April 2015

Time: **14:30 - 16:00**

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

Abstract: In this talk I will present a ‘distributed’ variant of the so-called gossip problem. The problem concerns n agents. They all know one piece of information (a secret), which is unknown to the others, and they communicate by one-to-one interactions (e.g., telephone calls). After each interaction the two agents involved in it learn all secrets the other agent knows at the time of the call. The problem consists in finding sequences of calls (under different constraints, typically minimal length) which disseminate all the secrets among the agents in the group. It was widely investigated in the 70s and 80s.

The standard formulation of the problem assumes a centralized perspective: a planner finds a suitable sequence of calls and schedules agents’ calls accordingly. I will present the problem from a decentralized perspective: agents perform calls not according to a centralized schedule, but following individual epistemic protocols they run in a distributed fashion. These protocols tell the agents whom to call next depending on what they know, or do not know, about the information state of the other agents in the group. I will elaborate on this model as a useful abstraction to understand processes of information diffusion in groups.

The talk reports on joint work with Maduka Attamah (University of Liverpool), Wiebe van der Hoek (University of Liverpool), Hans van Ditmarsch (LORIA), Krzysztof Apt (CWI). This is work-in-progress and I will put emphasis on open problems and future directions of research.

**MARCH 31st 2015, LogiCIC-LIRa Lunch Talk**

Speaker: **Thomas Bolander**

Title: **Complexity Results in Epistemic Planning**

Date: Tuesday 31 March 2015

Time: **13:00 - 14:30**

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

Abstract: Epistemic planning is a very expressive framework that extends automated planning by the incorporation of dynamic epistemic logic (DEL). We provide complexity results on the plan existence problem for multi-agent planning tasks, focusing on purely epistemic actions with propositional preconditions. We show that moving from epistemic preconditions to propositional preconditions makes it decidable, more precisely in EXPSPACE. The plan existence problem is PSPACE-complete when the underlying graphs are trees and NP-complete when they are chains (including singletons). We also show PSPACE-hardness of the plan verification problem, which strengthens previous results on the complexity of DEL model checking.

This is joint work with Martin Holm Jensen and Francois Schwarzentruber.

**MARCH 12th 2015, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Christian List**

Title: **From Degrees of Belief to Beliefs: Lessons from Judgment-Aggregation Theory**

Date: Thursday 12 March 2015

Time: **15:00 - 17:00**

Location: **Science Park 904**, **Room B0.207**

Abstract: The full paper, with an abstract, is available at:

http://personal.lse.ac.uk/list/PDF-files/Binarization.pdf

**MARCH 11th 2015, SEMINAR MEETING (joint LogiCIC-LIRa seminar) **

Speaker:

**Hans van Ditmarsch**

Title: **Five Funny Bisimulations**

Date: Wednesday 11 March 2015

Time: **11:30 - 13:00**

Location: Room F1.15, ILLC, Science Park 107, Amsterdam

Abstract: We present various recent work proposing adjustments to the standard notion of bisimulation in order to have proper structural correspondents with epistemic, or epistemically motivated, modalities: contingency bisimulation, awareness bisimulation, plausibility bisimulation, refinement, and bisimulation for sabotage.

**MARCH 6th 2015, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Roberto Ciuni** (Visiting Scholar ILLC)

Title: **Plausibility Trees and Simple Future**

Date and Time: Friday, March 6, 2015, **14:30-16:00**

Venue: Science Park 107, Room **F1.15**

**Abstract.** In this talk I introduce a new formal setting for simple-future sentences in branching time. The new setting combines a quantification over histories–which is available in all branching-time logics–together with a plausibility relation between histories, so that a sentence like (a) ‘There will be a sea battle’ is taken to mean ‘There is a history h such that for all the histories h’ that are equally or more plausible than h, there is a later moment where it is the case that there is a sea battle’ (the implicit condition here is that we consider histories passing through the moment of valuation.) I present the new semantics against the background of current branching-time semantics, and I show that the new setting can help overcome some conceptual problems current branching-time semantics have in modelling ‘future contingents’ – that is simple-future sentences about states of affairs that are neither impossible nor inevitable.

**FEBRUARY 27th 2015, SEMINAR MEETING (joint LogiCIC-LIRa seminar) cancelled**and moved to MARCH 6th.

(overlap with Heyting Day, see http://phil.uu.nl/~albert/Heyting_Day/ )

**DECEMBER 5th 2014, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Soroush Rafiee Rad** (University of Amsterdam, LogiCIC Team Member)

Title: **Forming Rational Belief From First Order Probabilistic Evidence**

Date and Time: Friday, December 5, 2014, **14:30-16:00**

Venue: Science Park 107, Room **F1.15**

**Abstract:** In this talk we investigate the inference processes for probabilistic evidence. We will look into generalisation of two well studied inference processes (Maximum Entropy and Centre of Mass) to first order languages and will investigate the complexity of evidence sets for which such generalisations are possible.

**NOVEMBER 24-26, THIRD LogiCIC WORKSHOP, Amsterdam**

Correlated Information Change - LogiCIC Project workshop - Amsterdam, 24-26 November 2014

**NOVEMBER 20-21, SYNTHESE CONFERENCE, Amsterdam**

Satellite Event : Synthese Conference on Qualitative and Quantitative Methods in Formal Epistemology - Amsterdam, 20-21 November 2014

**OCTOBER 2nd 2014, MINI-WORKSHOP on The Logical Dynamics of Information, Agency and Interaction**

**LogiCIC-LIRa affiliated Workshop**

Date and Time: October 2 (9:30-16:00)-October 3 (9:30-16:00), 2014

Venue: Science Park 107,Room F1.15

**Speakers**:** **Jan van Eijck, Kaile Su, Chanjuan Liu, Pingzhong Tang, Fenrong Liu, Sonja Smets, Alexandru Baltag, Chenwei Shi, Malvin Gattinger, Zoe Christoff, Paolo Galeazzi, Soroush Rafiee Rad, Nina Gierasimczuk, Bryan Renne, Johan van Benthem

For programme and abstracts click here

**SEPTEMBER 25th 2014, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Thomas Icard** (Stanford University)

Title: **Comparative Probability in Language and Action**

Date and Time: Thursday, September 25, 2014, **15:30-17:00**

Venue: Science Park 107, Room **F1.15**

**Abstract: **A number of seminal figures in the history of probability, including Keynes, de Finetti, Savage, and others, held that comparative probability judgments — as expressed, e.g., by statements of the form ‘E is more likely than F’ — might be, in one way or another, more fundamental than quantitative probabilistic judgments. Such comparative judgments have mostly been studied in relation to quantitative notions, viz. representation theorems. After briefly discussing how this older work on representation theorems relates to contemporary questions in linguistic semantics about what locutions like ‘E is more likely than F’ mean, I will then argue that we need a better understanding of normative considerations concerning comparative probability that is, at least potentially, independent of quantitative representations.

I will present a new result — analogous to, but requiring weaker assumptions than, Dutch book arguments for standard quantitative probability — characterizing exactly when an agent maintaining given comparative judgments is susceptible to a blatant kind of pragmatic incoherence. It turns out that quantitative representability can be motivated in this way, without presupposing quantitative representation on the part of the agent. Finally, I will illustrate how this result might bear on the aforementioned questions in semantics, as well as more general questions about the role of qualitative probability judgments in practical reasoning.

**SEPTEMBER 9th 2014, SEMINAR MEETING (joint LogiCIC-LIRa seminar) with 2 talks by Jeremy Seligman and Thomas Ågotnes**

Venue: Science Park 107, Room **F1.15**

Date and Time: **Tuesday**, September 9, 2014, **12:00-14:00 **:

12:00-13:00: **Jeremy Seligman** (University of Auckland)

Title: **Exploiting and maintaining network Ignorance**

Abstract: Suppose you want to send a message to someone in your extended social network secretly i.e. without others coming to know it. Can this be done and if so how? Addressing this question raises many others. What do you know about the structure of the network and the knowledge of other agents? What kind of message can you send? And what do you really mean by “secretly”? Is it acceptable that other agents get to know some but not all of your message? What sense can be given to their knowing none of it? We offer a formalisation of perhaps the simplest answers to these questions, which exhibits interesting complexity nonetheless, in particular concerning the concepts of potential social knowledge. (Joint work with Thomas Agotnes and Mostafa Raziebrahimsaraei.)

13:00-14:00: **Thomas Ågotnes** (University of Bergen)

Title: **From Distributed to Common Knowledge**

Abstract: The topic of the talk is standard notions of group knowledge and belief, with a focus on distributed knowledge. First, I will discuss a natural range of group belief concepts with distributed and general ("everybody-believes") as the two extreme endpoints and with many intermediate concepts in between. Distributed knowledge is sometimes described as what the members of the group would know of they "pool their knowledge together". This is inaccurate at best: for example, it is consistent that a group has distributed knowledge of a Moore sentence involving one of the members of the group (a sentence which cannot be known by that member, no matter how much "pooling" has taken place). In the second part of the talk, based on joint work with Yi Wáng, I discuss a new group modality that actually captures what is true after the group have fully shared their information with each other -- after their distributed knowledge has been resolved. A key question is: when does distributed knowledge become common knowledge?

**JUNE 19th 2014, LogiCIC/LIRa mini-workshop on The Dynamics of Information States**

Time: **15:00 — 18:00**

Location: room K.06, Bungehuis, Spuistraat 210, Amsterdam https://rooster.uva.nl/locationinfo/908K06

Co-sponsored by the NWO VIDI project on Reasoning about Quantum Interaction

**15:00** Ben Rodenhäuser (University of Amsterdam): Introduction

**15:10** Branden Fitelson (Rutgers University) : Knowledge from Non-Knowledge

First, I will review some historical examples that appear to be cases of knowledge obtained via (rational) inference from premises (some of) which are not known. Then, I will discuss a popular strategy for responding to such cases. Finally, I will pose a dilemma for this popular strategy.

**16:00** Break

**16:10** Wesley H. Holliday (UC Berkeley): Knowledge, Time, and Paradox: Introducing Sequential Epistemic Logic

In this talk, I will introduce Sequential Epistemic Logic (SEL), a generalization of Dynamic Epistemic Logic (DEL) aimed at describing the full temporal sequence of agents’ epistemic states, including agents’ changing knowledge of their own and others’ past and future epistemic states, in terms of the kinds of epistemic transformations studied in DEL. I will focus on the SEL analogue of Public Announcement Logic. After discussing some objections to DEL analyses of epistemic paradoxes (in particular, the Knowability Paradox and Surprise Exam Paradox), I will show how SEL overcomes these objections and provides new distinctions related to the phenomenon of “unsuccessful” information updates.

**17:00** Break

**17:10** Hans Rott (Universität Regensburg): Imperfect Discrimination and the Vagueness of Belief

The classical theory of theory change due to Alchourrón, Gärdenfors and Makinson (“AGM”) has been widely known as being characterised by two packages of postulates. The basic package consists of six postulates and is very weak, the full package adds two further postulates and is very strong. Tracing the ideas of imperfect discrimination of the plausibilities of possible worlds, and of imperfect discrimination of the entrenchments of beliefs, I argue that for the interest in two distinct weakenings of the full AGM theory (which are still a lot stronger than the basic theory). The notion of imperfect discrimination raises the question regarding its relation to the notion of vagueness, here: the vagueness of the concept of belief. I try to give an answer.

**18:00** End of Workshop

**JUNE 10th 2014, LogiCIC/LIRa mini-workshop on Formal Epistemology**

Date and Time: Tuesday, June 10, 2014, 13:00-17:30

Venue: Science Park 107, Room F1.15

**13:00-14:30:**

Speaker: **Branden Fitelson** (Rutgers University)

Questions and answers session of the Coherence Tutorial

**15:00-15:40**

Speaker: **Jason Konek** (University of Bristol)

Title: **Non-additive scoring rules for comparative belief**

**Abstract: **According to Bayesian orthodoxy, an agent’s comparative beliefs must be representable by probability function p, in the sense that she thinks that X is no more likely than Y (or X is strictly less likely than Y) only if p(X) is less than or equal to p(Y) (or p(X) is strictly less than p(Y)). Inspired by the accuracy-dominance arguments of Joyce (1998, 2009), Predd et al. (2009) and Schervish et al. (2009), Fitelson and McCarthy (2014) ground coherence requirements for comparative belief by showing that violating these requirements amounts to squandering accuracy. But their requirements are weaker than the Bayesian’s. In this talk, we propose amending one of Fitelson and McCarthy’s core assumptions, in hopes of providing an accuracy-dominance argument for full-throated Bayesian orthodoxy about comparative belief. In particular, Fitelson and McCarthy restrict their attention to “additive” measures of inaccuracy, which first (i) measure the inaccuracy of individual judgments between pairs of propositions — X ≺ Y , X ≈ Y or X ≻ Y — and then (ii) weigh up these individual scores in some way, to provide a “summary statistic” which captures her comparative belief ordering’s overall accuracy. We will motivate and explore inaccuracy measures for comparative belief that do not take this additive form.

**15:50-16:30 **Speakers: **Jason Konek and Ben Levinstein** (University of Bristol)

Title: **The Foundations of Epistemic Decision Theory**

**Abstract: **According to accuracy-first epistemology, accuracy is the fundamental epistemic good. Epistemic norms — Probabilism, Conditionalization, the Principal Principle, etc. — have their binding force in virtue of helping to secure this good. To make this idea precise, accuracy-firsters invoke Epistemic Decision Theory (EpDT) to determine which epistemic policies are the best means toward the end of accuracy. Hilary Greaves and others have recently challenged the tenability of this programme. Their arguments purport to show that EpDT encourages obviously epistemically irrational behavior. We develop firmer conceptual foundations for EpDT. First, we detail a theory of praxic and epistemic good. Then we show that, in light of their very different good-making features, EpDT will evaluate epistemic states and epistemic acts according to different criteria. So, in general, rational preference over states and acts won’t agree. Finally, we argue that based on direction-of-fit considerations, it’s preferences over the former that matter for normative epistemology, and that EpDT, properly spelt out, arrives at the correct verdicts in a range of putative problem cases.

**16:40-17:20** Speaker: **Krzysztof Mierzewski **(University of Amsterdam)

Title: **Bridging Bayesian Probability and AGM Revision via Stability Principles**

(joint work with Alexandru Baltag)

**Abstract:** This talk concerns the relationship between probabilistic (Bayesian) and qualitative (AGM-based) models of belief dynamics. I address the question of how AGM belief revision operators can be related to Bayesian conditioning, in order to flesh out some (in)compatibilities between the Bayesian and AGM-based formalisms.

This is done by analysing the behaviour of acceptance rules, which map probabilistic credal states to qualitative representations of belief. Given an acceptance rule, the ideal of compatibility between Bayesian conditioning and qualitative revision is embodied by the tracking property, which imposes a commutativity requirement to ensure that conditioning and revision agree modulo the acceptance map.

I focus on an acceptance rule based on the notion of stably high probability, due to Leitgeb. As a consequence of a ‘No-Go’ theorem by Lin & Kelly, Leitgeb’s rule does not allow AGM revision to track conditioning. Nonetheless, given this rule’s inherent attractiveness as an acceptance principle and its close connection to AGM revision, I consider some ways in which one may circumvent the No-Go Theorem and use the rule so as to approximate agreement between AGM and Bayesian conditioning.

One rather natural such method – threshold-raising – fails, which poses some difficulties for the ‘peace project’ between Bayesian and AGM-compliant operators. However, another interesting connection exists: I show that there is a sense in which AGM revision derives from (1) Leitgeb’s rule, (2) Bayesian conditioning, and (3) a version of the maximum entropy principle. This suggests that one could study qualitative revision operators as special cases of Bayesian reasoning which naturally arise in situations of information loss or incomplete probabilistic specification of the agent’s credal state.

**JUNE 2014, PROJECT SEMINAR MEETINGS**

We have the pleasure to invite you to attend the tutorial and ILLC-project on Coherence by **Branden Fitelson** (Professor of Philosophy at Rutgers University).

Please find a short description below. We plan about 2 to 3 meetings every week in June.

During the first week, Branden will give an overview of the different parts of his new book. These first sessions are planned on:

Tu 3 June: 11h-13h

We 4 June: 13h-15h

Th 5 June: 13h-15h

Venue: Amsterdam, Science Park 107, Room F1.15

More information is available at http://uva.us5.list-manage.com/track/click?u=4b05abc4557cd64a12e62f565&id=227b000405&e=550792e49d

Short Description: This project revolves around the contemporary literature on (formal) coherence. Specifically, we will focus on recent applications of "epistemic utility theory" to the problem of grounding synchronic coherence requirements for full belief, comparative confidence, and numerical credence (viz., degree of belief), respectively. The course will be a mixture of introductory lectures by the instructor, presentations by students, and group discussion. The instructor will be distributing a draft book manuscript which will serve as the primary source for readings and exercises (secondary readings and background materials will be provided on the project webpage: http://uva.us5.list-manage.com/track/click?u=4b05abc4557cd64a12e62f565&id=fc25918a43&e=550792e49d).

**MAY 15th 2014, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Bryan Renne** (University of Amsterdam/University of British Columbia), http://bryan.renne.org/

Title: **Dynamic Justification Logic for Formal Epistemology**

Date and Time: Thursday, May 15, 2014, **15:30-17:00**

Venue: Science Park 107, Room **F1.15**

**Abstract:**

In this talk, which covers joint work with Alexandru Baltag and Sonja Smets (both ILLC Amsterdam), I will present progress toward a logical toolkit for reasoning about knowledge, belief, and evidence. My goal will be to demonstrate in simple terms how our work can be applied to representing and reasoning about key aspects of Keith Lehrer’s “Theory of Knowledge,” 2nd ed., Westview Press, 2000.

References:

1. (with Alexandru Baltag and Sonja Smets) The Logic of Justified Belief, Explicit Knowledge, and Conclusive Evidence. Annals of Pure and Applied Logic, 165(1):49–81, 2014.

=> PDF: http://bryan.renne.org/docs/brs-ConclusiveEvidence.pdf

=> DOI: http://dx.doi.org/10.1016/j.apal.2013.07.005

2. (with Alexandru Baltag and Sonja Smets) The Logic of Justified Belief Change, Soft Evidence and Defeasible Knowledge. In L. Ong and R. de Queiroz, editors, Proceedings of the 19th Workshop of Logic, Language, Information and Computation (WoLLIC 2012), volume 7456 of Lecture Notes in Computer Science, pages 168–190, Buenos Aires, Argentina. Springer-Verlag Berlin Heidelberg, 2012.

=> PDF: http://bryan.renne.org/docs/brs-jbc-wollic2012.pdf

=> DOI: http://dx.doi.org/10.1007/978-3-642-32621-9_13

**MARCH 26th 2014, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

We'll have a double seminar including a lecture by Prof. Francesca Poggiolesi (CEPERC) and a lecture by Prof. Brian Hill (HEC Paris)

Speaker: **Francesca Poggiolesi **(*CEPERC – UMR 7304*)

Title: **An alternative proof-theoretical approach to standard conditional logics**

**Abstract:** Conditional logics, which have a long and venerable history [5, 2, 3], have been introduced to capture counterfactual sentences, i.e. conditionals of the form “if A were the case, then B would be the case”, where A is false. If we interpret counterfactuals as material implications, we have that all counterfactuals are trivially true, and this is an unpleasant conclusion. By means of conditional logics, on the other hand, we can give a different and meaningful interpretation of counterfactual sentences.There are several different systems of conditional logics. Amongst them we focus on the system CK and its standard extensions, namely CK + {ID, MP, CS, CEM}. These systems have a simple and useful semantics. One just needs to consider a set of possible worlds W, and a selection function f; for each world i and each formula A, f selects the set of worlds of W which are closer to i given the information A. Thus a counterfactual sentence A > B is true at a world i if, and only if, B is true at all those worlds that are closer to i given the information A.

In this talk we aim at presenting sequent calculi for the system CK and all of its extensions. These calculi are based on and fully exploit the simple semantics interpretation of such systems. Moreover, they are contraction-free, weakening-free and cut-free; finally, their logical rules are all invertible. As far as we know the only other sequent calculi that have been proposed for the system CK and its extensions are those of Olivetti and al. [4] (sequent calculi for other systems of conditional logics have been proposed by e.g. [1]). With respect to these calculi the main differences consist in a lighter formalisms and simpler logical rules to manipulate.

By using the same technique adopted for the sequent calculi, we will also briefly show how to construct natural deduction calculi for CK + {ID, MP, CS, CEM}.

References

[1] Crocco, G. and Lamarre, P. On the connection between non-monotonic inference systems and conditional logics. In Proceedings of the 3rd International Conference on Principles of Knowledge. Representation and Reasoning, B. Nebel and E. Sandewall Ed., 565-571, 1992.

[2] Lewis, D. Counterfactuals. Basil Blackwell, 1973.

[3] Nute, D. Topics in Conditional Logic. Reidel, Dordrecht, 1980.

[4] Olivetti, N., Pozzato, G. L., and Schwind, C. B. A sequent calculus and a

theorem prover for standard conditional logics, ACM Transactions on Computational Logic (TOCL) 8 : 557-590, 2007.

[5] Stalnaker, R. A theory of conditionals, American Philosophical Quarterly, Monograph Series no.2, Blackwell, Oxford, 98-112, 1968.

Speaker: **Brian Hill **(*HEC Paris*)

Title: **Confidence in Beliefs and Decision Making**

**Abstract:** The standard representation of beliefs in decision theory and much of formal epistemology, by probability measures, is incapable of representing an agent's confidence in his beliefs. However, as shall be argued in this talk, the agent's confidence in his beliefs plays, and should play, a central role in many of the most difficult decisions which we find ourselves faced with. The aim of this talk is to formulate a representation of agents' doxastic states and a (axiomatically grounded) theory of decision which recognises and incorporates confidence in belief. Time-permitting, consequences for decision in the face of radical uncertainty will be examined.

Date and Time: Wednesday, March 26, 2014, **16:30-18:00**

Venue: Science Park 107, Room **F1.15**

**FEBRUARY 21th 2014, LogiCIC-lunch talk**

Speaker: **Vincent Hendricks **(University of Copenhagen)

Title: **Science Bubbles**

Date and Time: FRIDAY, February 21, 2014, **12:00-13:30**

Venue: Science Park 107, Room **F1.15**

**Abstract:** Much like the trade and traits of bubbles in financial markets, similar bubbles appear on the science market. When economic bubbles burst, the drop in prices causes the crash of unsustainable investments leading to an investor confidence crisis possibly followed by a financial panic. But when bubbles appear in science, truth and reliability are the first victims. This paper explores how fashions in research funding and research management may turn science into something like a bubble economy.

Joint work with David Budtz Pedersen

**FEBRUARY 5th 2014, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Barteld Kooi **(University of Groningen)

Title: **The ambiguity of knowability**

Date: **Wednesday**, February 5, 2014

Time: **16:30-18:00**

Location: Room **F1.15**, ILLC, Science Park 107, Amsterdam

**Abstract: **In this talk I will argue that the Verification Thesis (all truths are knowable) is only susceptible to Fitch’s Paradox if one conflates the de re and de dicto interpretation of knowability. A formalization shows that if one treats knowability as a complex second-order predicate, then the paradox falls apart.

**JANUARY 2014, Lecture and visit by F. Liu (cancelled)**

**DECEMBER 22 2013, MINI-WORKSHOP (joint LogiCIC-LIRa sponsored meeting)**

Title: **Knowledge, Argumentation & Games workshop**

Date: Wednesday, December 11, 11.15am – 6.10pm

Location: **Roeterseiland – Building E, room 0.20, Roetersstraat 11, 1018 WB Amsterdam**.

Website: **https://sites.google.com/site/knowledgeargumentationgame/the-workshop**

**Description:** The central topic of this workshop is knowledge, argumentation and games. The workshop will create an opportunity for philosophers and logicians to meet and present their work on this topic. We are interested in already-established work as well as ongoing work on the concepts of knowledge, argumentation and games as well as their relations.

**DECEMBER 2-4 2013, SECOND LogiCIC WORKSHOP, Amsterdam**

Social Dynamics of Information Change - LogiCIC Project workshop - Amsterdam, 2-4 December 2013

**NOVEMBER 14th 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Rohit Parikh** (Brooklyn College and CUNY Graduate Center)

Title: **Knowledge from Inadvertant and Strategic Communication**

Date: Thursday 14 November 2013

Time: **15:30 - 17:30**

Location: Room **F1.15**, ILLC, Science Park 107, Amsterdam

**Abstract**: A popular model in knowledge updating is where we receive true information from a trusted source. The work of Jan Plaza and others, and the AGM theory both use this paradigm. This is also the method used by Geanakoplos and Polemarchakis, and RP and Krasucki, in their “activist” versions of Aumann’s result. However, literature is rife with examples where information is revealed inadvertantly so that the one revealing information is not doing it deliberately but is tricked into it. We give examples from Shakespeare, Saki and Birbal. A second departure from the paradigm arises when the two sources do not share objectives, so that the Gricean assumption of cooperation does not hold. Nonetheless, some information can get across when the interests of the two parties overlap at least in part. We report on some theoretical work in this area, some of it falling under the heading of “cheap talk,” and offer a model.

**OCTOBER 31st 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Sven Ove Hansson** (Royal Institute of Technology, Stockholm)

Title: **Descriptor revision and epistemic accessibility**

Date: Thursday 31 October 2013

Time: **16:00 - 18:00**

Location: Room **F1.15**, ILLC, Science Park 107, Amsterdam

**Abstract**: A framework for belief change is introduced in which the selection mechanism operates directly on potential outcomes rather than on possible worlds or maximal consistent subsets of the original belief set. Success conditions are expressed with (metalinguistic) belief descriptors that are built from atomic sentences of the form Bp where p is a sentence in the object language. In this way a general form of belief revision is obtained that includes revision and contraction as special cases. Revision by a sentence p is expressed with the success condition {Bp}, multiple revision has success conditions of the form {Bp1, Bp2…}, contraction has {-Bp}, etc. New operations can also be defined, such as “making up one’s mind” {Bp V B-p}. A distance-based semantic model for descriptor revision is proposed in which the outcome is the closest potential outcome in which the success condition is satisfied. The outcome set (set of belief sets that are potential outcomes of belief change) is taken as given. A generalization of epistemic entrenchment, epistemic accessibility, is defined that applies to all success conditions. It has standard entrenchment (for contraction) as a special case. The new approach is motivated by problems in previous models (such as the recovery property) that are avoided in the new framework.

**SEPTEMBER 26th 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Rasmus Rendsvig **(University of Amsterdam)

Title: **DEL-based state machines and their application in modeling group reasoning and choice**

Date and Time: Thursday, September 26, 2013, **15:30-17:30**

Venue: Science Park 107, Room **F1.15**

**Abstract:** The talk will be comprised of two parts.

In part I, a notion of DEL-based state machines will be introduced and situated. The key notion is that of “transition rules”. A set of transition rules picks a next transition (update) as a function of the formulas satisfied at a given state, hereby specifying the subsequent state(s). Hence defining a DEL-based state machine is not done by directly providing a state transition function from states to states, but rather by specifying a set of rules triggered by local features. It will be shown how DEL-based transition systems may mimic traditional types of state machines (finite/infinite, deterministic/indeterministic), and their “tree generation power” is compared to the protocol-based approach known from the DEL literature.

In part II, it will be shown how transition rules as “knowledge-based programs” may be used to define agent types. In this part of the talk, we will move to a specific DEL setting using epistemic plausibility models and action plausibility models with postconditions. Using this setting, it will be shown how DEL-based state machines may be used to define completely specified models of agent reasoning and choice. This is exemplified by a DEL-based state machine that captures the reasoning and choices occuring in an informational cascade-prone environment. As the state machine is formally fully specified, the construction allows for rigid proofs pertaining to informational cascade dynamics.

**SEPTEMBER 12th 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Emiliano Lorini **(IRIT-CNRS, University of Toulouse)

Title: **On the epistemic foundation for iterated weak dominance: an analysis in a logic of individual and collective attitudes**

Date and Time: THURSDAY, September 12, 2013, **15:30-17:30**

Venue: Science Park 107, Room **F1.15**

**Abstract**: This paper proposes a logical framework for representing static and dynamic properties of different kinds of individual and collective attitudes. A complete axiomatization as well as a decidability result for the logic are given. The logic is applied to game theory by providing a formal analysis of the epistemic conditions of iterated deletion of weakly dominated strategies (IDWDS), or iterated weak dominance for short. The main difference between the analysis of the epistemic conditions of iterated weak dominance given in this paper and other analysis is that we use a semi-qualitative approach to uncertainty based on the notion of plausibility first introduced by Spohn, whereas other analysis are based on a quantitative representation of uncertainty in terms of probabilities.

**MAY 21st 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Fenrong Liu **(Tsinghua University)

Title: **Facebook and the epistemic logic of friendship**

Date and Time: Tuesday, May 21, 2013, **15:30-17:30**

Venue: Science Park 107 (new ILLC location), Room **F1.15**

**Abstract**:

In this talk I will present a two-dimensional modal logic for reasoning about the changing patterns of knowledge and social relationships in networks organised on the basis of a symmetric "friendship" relation, providing a precise language for exploring "logic in the community". Agents are placed in the model, allowing us to express such indexical facts as "I am your friend" and "You, my friends, are in danger".

The purpose of developing such a language is to investigate a number of conceptual issues that arise when considering communication between agents in social networks, both from one agent to another, and broadcasts to socially-defined groups of agents, such as the group of my friends. We extend the treatment of such communications to questions, in which agents are taken to be sincere and cooperative interlocutors, and consider network structure changing operations such as adding and deleting friends (with the permission of other agents) and, finally, explore the effect of all this on the concept of common knowledge, which is more varied and rich in the social network setting. These issues are illustrated by a number of examples about office gossip, cold-war spy networks and Facebook.

This is joint work with Jeremy Seligman and Patrick Girard. (PDF of the paper)

**APRIL 2nd 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Marcel Boumans** (University of Amsterdam)

Title: **Rational consensus of expert judgments in economics**

Room: Science Park 107 (NEW ILLC LOCATION), room F1.15

Time: **TUESDAY**, 2 April, 15:30-17:30

**Abstract**: The aim of the “rational-consensus method” is to produce “rational consensus”, that is, a “mathematical aggregation”, by weighing the opinion of each expert on the basis of his or her knowledge and ability to judge relevant uncertainties. Over the last fifteen years, Roger M. Cooke has developed procedures to support the formal application of expert judgment. For the kind of cases Cooke has worked on, expert judgment is used to obtain results from experiments and/or measurements, which are physically possible, but not performable in practice. Such experiments are “out of scale” financially, morally, or physically in terms of time, energy, distance, etc. Since these experiments cannot in fact be performed, experts are uncertain about the outcomes, and this uncertainty is quantified in a formal expert judgment exercise. This method should be constrained by “principles for rational consensus”. One of these principles is “Empirical control.” This principle entails the measurement of the performance of the experts by the expert’s assessment of “seed variables.” The disadvantage of the rational-consensus method in social science is the lack of agreed upon seed variables, and that it does not instead use the shared knowledge captured by models. Moreover, there seems to be ample evidence that combining models with expert judgments leads to better judgments. This seems even more evident with respect to forecasts.

**MARCH 21st 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Giacomo Sillari** (Scuola Normale Superiore di Pisa)

Title: **You better play 7: mutual versus common knowledgeof advice in a weak-link experiment**

Room: Science Park 107 (NEW ILLC LOCATION), room F1.15

Time: Thursday, 21 March, 15:30-17:30

**Abstract**: This paper presents the results of an experiment on mutual versus common knowledge of advice in a two-player weak-link game with random matching. Our experimental subjects play in pairs for thirteen rounds. After a brief learningphase common to all treatments, we vary the knowledge levels associated with external advice given in the form of a suggestion to pick the strategy supporting the payoff dominant equilibrium. Our results are somewhat surprising and can be summarized as follows: in all our treatments both the choice of the efﬁciency-inducing action and the percentage of efﬁcient equilibrium play are higher with respect to the control treatment, revealing that even a condition as weak as mutual knowledge of level 1 is sufﬁcient to significantly increase the salience of the efﬁcient equilibrium with respect to the absence of advice. Furthermore, and contrary to our hypothesis, mutual knowledge of level 2 induces, under suitable conditions, successful coordination more frequently than common knowledge.

**FEBRUARY 14th 2013, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Mamoru Kaneko**, (Tsukuba University)

Title: **Epistemic Logic and Inductive Game Theory**

Time: Thursday, February 14, 2013, **15:30-17:30**

Location: Science Park 904, Room **D1.115**

**Abstract**: “Bounded rationality” appears in many forms in individual thinking and behavior in social situations. We should take it seriously for future developments of game theory and related fields. Its central part is not only in cognitive and epistemic abilities of individuals but also in social interactions. In this talk, I will discuss a few foundational problems related to “bounded rationality” from the perspective of epistemic logic and inductive game theory.

**JANUARY 31st 2013 SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Janusz Czelakowski **(Opole University)

Title:** Freedom and Enforcement in Action - Elements of Formal Action theory.**

Room: Science Park 904, room **C1.112**

Time: Thursday, 31 January 2013, **15:30-17:30**

**Abstract:**

Stit semantics gives an account of action from a certain perspective: actions are seen not as operations performed in an action system and yielding new states of affairs, but rather as selections of pre-existent histories (or trajectories) of the system in time. Stit semantics is therefore time oriented, and time, being a situational component of action, plays a special role in it. In the talk an approach to action theory which stems from formal linguistics and dynamic logic is presented. An elementary action system is a triple (*) (W, R, A), where W is a set of states, R is a binary relation on W called the transition relation between states, and A is a non-empty family of binary relations on W. (*) is thus a multi-modal frame in which the relation R is distinguished. The members of A are called atomic actions of the system (*). A compound action (over (*)) is a set of finite sequences of atomic actions from A. Every compound action is thus viewed as a formal language over the alphabet A. In ordered action systems the set of states W is additionally partially ordered. A situational action system is an extension of an elementary action system which takes into account the situational envelope in which actions are immersed. A comparison with stit semantics is discussed. In the talk an approach to deontic logic is presented according to which actions (or deeds), and not states of affairs, bear deontic values (as being obligatory, forbidden, permitted). The notion of an atomic norm and its relationship with the above interpretation of the deontic operators is discussed. The term norm receives a wider meaning than in jurisprudence and encompasses moral norms, linguisitic norms, social norms - providing patterns of behaviour in social communities, conventions, etiquettes etc. In our approach norms play a role similar to that of rules of inference in logic (but the analogy is rather loose) – norms are rules of action; they guide actions and determine circumstances under which some actions are permitted, forbidden or obligatory. To each atomic norm a certain normative proposition is assigned; norms however are not reducible to propositions.

**DECEMBER 14-15 2012, The kick-off LogiCIC workshop, Amsterdam**

*Belief Change in Social Context* - LogiCIC Project kick-off workshop - Amsterdam, 14-15 December 2012

**DECEMBER 6th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar, two talks)**

We will have a long LogiCIC/LIRa joint session (from 15:00 to 18:00) with two talks by **Thomas Bolander** and **Hans van Ditmarsch**.

Date and time: Thursday, December 6th, 2012, 15:00-18:00

Location: **Room ****B0.201**, Science Park 904, Amsterdam

INFORMATION ABOUT THE FIRST TALK:

Time: **15:00-16:30**

Speaker: **Thomas Bolander**

Time: Title: **Don’t Plan for the Unexpected: Planning Based on Plausibility Models**

**Abstract**:

We present a framework for automated planning based on plausibility models, as well as algorithms for computing plans in this framework. Our plausibility models include postconditions, as ontic effects are essential for most planning purposes. The framework presented extends a previously developed framework based on dynamic epistemic logic (DEL), without plausibilities/beliefs. In the pure epistemic framework, one can distinguish between strong and weak epistemic plans for achieving some, possibly epistemic, goal. By taking all possible outcomes of actions into account, a strong plan guarantees that the agent achieves this goal. Conversely, a weak plan promises only the possibility of leading to the goal. In real-life planning scenarios where the planning agent is faced with a high degree of uncertainty and an almost endless number of possible exogenous events, strong epistemic planning is not computationally feasible. Weak epistemic planning is not satisfactory either, as there is no way to qualify which of two weak plans is more likely to lead to the goal. This seriously limits the practical uses of weak planning, as the planning agent might for instance always choose a plan that relies on serendipity. In the present paper we introduce a planning framework with the potential of overcoming the problems of both weak and strong epistemic planning. This framework is based on plausibility models, allowing us to define different types of plausibility planning. The simplest type of plausibility plan is one in which the goal will be achieved when all actions in the plan turn out to have the outcomes a priori believed most plausible by the agent. This covers many cases of everyday planning by human agents, where we—to limit our computational efforts—only plan for the most plausible outcomes of our actions.

INFORMATION ABOUT THE SECOND TALK:

Time: **16:30-18:00**

Speaker: **Hans van Ditmarsch**, LORIA, Nancy & (associate) IMSc, Chennai

Title: **Refinement modal logic**

**Abstract:**This is joint work with Laura Bozzelli, Tim French, James Hales, and Sophie Pinchinat.In this talk I will present refinement modal logic. A refinement is like a bisimulation, except that from the three relational requirements only ‘atoms’ and ‘back’ need to be satisfied. Our logic contains a new operator ‘forall’ in addition to the standard modalities box for each agent. The operator ‘forall’ acts as a quantifier over the set of all refinements of a given model. We call it the refinement operator. As a variation on a bisimulation quantifier, it can be seen as a refinement quantifier over a variable not occurring in the formula bound by the operator. The logic combines the simplicity of multi-agent modal logic with some powers of monadic second order quantification. We present a sound and complete axiomatization of multiagent refinement modal logic. There is an extension to the modal mu-calculus. It can be applied to dynamic epistemic logic: it is a form of quantifying over action models. There are results on the complexity of satisfiability, and on succinctness. We are highly interested in applications of this logic to epistemic planning.

**NOVEMBER 22nd 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Rohit Parikh** (Brooklyn College of CUNY and CUNY Graduate Center)

Title:** Epistemic Logic in Real Life and Literature**

Room: Science Park 904, room **D1.113**

Time: Thursday, 22 November, **15:30-17:30**

**Abstract:**

In his book Commodities and Capabilities, Amartya Sen points out that our well being depends not only on what we have, but also on what our capabilities are, to achieve goals which we value. But to achieve such goals, while we ourselves write and carry out the procedures, society serves as an operating system which implements the individual steps and provides appropriate subroutines. This role of society can be analyzed by standard logical techniques, e.g. Hoare Logic.

At a social rather than an individual level, when a planner wants people to act according to some socially desirable plan, the planner needs to make sure that people acting in terms of their own desires, their beliefs, and their capabilities, act in concordance with the plan. Thus managing knowledge states becomes a crucial element of such a plan. Enabling (or blocking) abilities can also be part of such a social plan.

We show how such managed knowledge states occur in the literature,giving examples from Shakespeare, Shaw, etc. We also present a technical result on creating knowledge states.

Finally we point to a remark by Socrates in Plato's Theaetetus about the Justified True Belief definition of knowledge. Far from endorsing this definition, Socrates presents an objection, different from Gettier's and anticipating a problem addressed by Turing in his classical 1936 paper. This objection of Socrates and our natural response to it bear on what we believe to be the ability of members of a society to carry out the individual steps of a personal algorithm.

**OCTOBER 12th, OCTOBER 15th and OCTOBER 18th 2012, THREE TUTORIAL SESSIONS**

Speaker: **Valentin Goranko** (Technical University of Denmark)

Title: **L****ogics for multi-agent systems**** **

Location: Science Park, Amsterdam

**THE SLIDES OF THE TUTORIAL ARE AVAILABLE ****HERE****.**

**Outline:**

**Lecture 1: **Friday, October 12th, 2012, 15:00 -17:00, room B0.203

1.1 Introduction: multi-agent systems (MAS).

1.2 Multi-agent epistemic logics (MAEL) with individual, distributed, and common knowledge (brief revision or more detailed coverage, depending on the audience background) incl:

- Language and formal Hintikka-Kripke semantics for multi-agent epistemic logics.

- Modelling, specifying, and analyzing the Muddy Children and Wise Men puzzles and some simple card game scenarios in MAEL.

1.3 Optionally (time permitting): Intro to dynamic epistemic logics.

**Lecture 2:** Monday, October 15th, 2012, 15:00 -17:00, in room B0.206

2.1 Multi-agent transition systems and concurrent game models.

2.2 Logics for strategic reasoning and abilities in MAS with complete information. The alternating-time temporal logic ATL.

**Lecture 3:** Thursday, October 18th, 2012, 13:30 - 15:30 in room B0.206

3.1 Some extensions and variations of ATL:

-- ATL with irrevocable strategies. Strategy context and reasoning under dynamic commitments and release of strategies.

-- ATL with incomplete and imperfect information.

-- Epistemic extensions of ATL.

3.2 State-variables based general framework for modeling and reasoning about MAS.

Depending on the composition, background and interests of the audience, some changes of this outline may occur during the course.

**OCTOBER 17th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar, two talks)**

We will have a long LogiCIC/LIRa joint session with two talks by **Valentin Goranko** and **Daisuke Bekki**. Please note that the two talks will be on a WEDNESDAY at 15:00.

Date and time: Wednesday, October 17th, 2012, 15:00 - 18:00

Location: Room A1.04, Science Park 904, Amsterdam

INFORMATION ABOUT THE FIRST TALK:

Speaker: **Daisuke Bekki** (Ochanomizu University)

Title: **Dependent type semantics: the framework**

**Abstract**:

This talk introduces dependent type semantics, a new framework of natural language semantics based on dependent type theory. Main features of dependent type semantics are the following:

1) it is dynamic: it analyzes E-type/donkey anaphora with well-formed representations.

2) it is proof-theoretic: entailments between the representations can be calculated without recourse to their models.

3) it is compositional: the semantic representations of sentences are derived from the lexicalized representations by a fixed number of combinatory rules.

4) it explains accessibility: accessibility/inaccessibility of anaphora is reduced to the structural differences between proofs.

These are achieved by a specific way of combining type theoretical approaches (cf. Ranta (1994)) and the continuation-based approaches (cf. de Groote (2006)) to dynamic binding. From the perspective of dependent type semantics, the source of dynamics in natural language is the dependence on proofs of the preceding discourses.

INFORMATION ABOUT THE SECOND TALK:

Speaker: **Valentin Goranko** (Technical University of Denmark)

Title: **Modeling the Dynamics of Information and Abilities of Players inMulti-Player Games**

**Abstract:**

I will discuss an early work towards a realistic treatment and logical formalization of the abilities of players to achieve objectives in multi-player games under incomplete, imperfect, or simply uncertain information that they may have about the game and about the course of the play. In this talk, after some motivating examples I will introduce a modeling framework for capturing the interplay between the dynamics of information and the dynamics of abilities of players. This framework takes into account both the a priori information of players with respect to the game structure and the empirical information that players develop over the course of an actual play. It associate with them respective information relations and notions of `a priori’ and `empirical’ strategies and strategic abilities. The empirical information relations are updated in the course of the play by a mechanism similar to the model update mechanism applied in Dynamic Epistemic Logic (DEL). Lastly, I will introduce a variation of the multi-agent logic ATL with incomplete information to formalize the reasoning in this framework and will briefly discuss the conceptual problem of model checking in that new logic under different assumptions about the abilities of the players to observe, remember, and reason.

**SEPTEMBER 27th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Guillaume Aucher** (University of Rennes)

Title: **DEL-sequents for progression, regression and epistemic**** planning**

Date and time: Thursday September 27th, 2012, 15:30 -17:30

Location: Room G0.05, Science Park, Amsterdam

**Abstract : **Dynamic Epistemic Logic (DEL) deals with the representation and the study in a multi-agent setting of knowledge and belief change.

It can express in a uniform way epistemic statements about:

(i) what is true about an initial situation

ii) what is true about an event occurring in this situation

(iii) what is true about the resulting situation after the event has occurred.

We axiomatize within the DEL framework what we can infer about (iii) given (i) and (ii), what we can infer about (ii) given (i) and (iii), and what we can infer about (i) given (ii) and (iii). These three inference problems are related to classical problems addressed under different guises in artificial intelligence and theoretical computer science, which we call respectively progression, epistemic planning and regression. Given three formulas F(i), F(ii) and F(iii) describing respectively (i), (ii) and (iii), we also show how to build three formulas which capture respectively all the information which can be inferred about (iii) from F(i) and F(ii), all the information which can be inferred about (ii) from F(i) and F(iii), and all the information which can be inferred about (i) from F(ii) and F(iii). We show how our results extend to other modal logics than K.

**SEPTEMBER 24th 2012, SEMINAR MEETING**

Speaker: **Guillaume Aucher** (University of Rennes)

Title: **Privacy and Epistemic Obligations**

Date and time: Monday September 24th, 2012, 16:00 -18:00

Location: Room B0.201, Science Park, Amsterdam

**Abstract : **We introduce a Dynamic Epistemic Deontic Logic to model privacy regulations for multi-agent systems. Our combined logic extends deontic logic with epistemic and dynamic update operators, to model the dynamics of knowledge and of privacy policies. In doing so, we resort to the action models of dynamic epistemic logic.

We show how to express epistemic norms and the conditional nature of norms. We can also specify and check whether a situation is compliant with respect to a privacy policy. We introduce the new notions of permitted and obligatory knowledge. They play a central role in privacy regulations.

Indeed, our main innovation is to define privacy policies in terms of the permitted and obligatory knowledge of the resulting epistemic state of the recipient of information, instead of defining them in terms of permitted and obligatory communicative acts. This allows us to determine the permitted and obligatory communicative acts in a given situation without having to specify permissions and prohibitions on all combinations of actions.

This is joint work with Guido Boella and Leon van der Torre.

**JUNE 11th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Nuel Belnap** (University of Pittsburgh)

Title: **Internalizing case-relative truth in CIFOL**

Date and time: Monday June 11th, 2012, 15:30 -17:30

Location: Room D1.114, Science Park 904, Amsterdam

The abstract is available **here**

**MAY 21st 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Branden Fitelson** (Department of Philosophy, Rutgers University, New Brunswick)

Title: **Accuracy, Coherence, and Evidence**

Date and time: Monday May 21st, 2012 16:00-18:00

Location: Room D1.113, Science Park 904, Amsterdam

**Abstract : **I will begin by rehearsing the traditional story about the relationship between accuracy norms (i.e., the truth norm), coherence norms (i.e., the deductive consistency norm), and evidential norms (i.e., a weak Lockean evidentialist thesis) for full belief. Then, I will discuss Ramsey-style reasons for being skeptical about an analogous story about partial belief (viz., credence). Next, I will describe an alternative story about the relationship between accuracy norms and coherence norms for credences (due to de Finetti, Joyce, and others). Finally, I will explain how an analogous story about full belief leads to an interesting new coherence norm that is weaker than deductive consistency, but much more intimately connected with evidential norms. Time permitting, various implications and applications of this new approach will be discussed.

This is joint work with Kenny Easwaran.

**MAY 15th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Vincent F. Hendricks** (Department of Philosophy, University of Copenhagen, Denmark)

Title: **Infobombs in Echo-chambers**

Date and time: Tuesday May 15, 2012 15:00-17:00

Location: Room (TBA), Science Park 904, Amsterdam

**Abstract : **Echo-chambers are results of extreme polarization among group members. While the phenomenon has proved robust, how to intervene in such chambers is still largely unexplored epistemic territory. Using three 3Ts, Time, Toning and Tact one may – under certain conditions – successfully “bomb” such chambers to either stall or actually dissolve the polarization effect. The original polarization may be the result of informational cascades for which a formal epistemic model is finally presented.

Joint work with Henrik Boensvang and Rasmus Rendsvig.

**APRIL 24th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Jens Ulrik Hansen** (Denmark)

Title: **Pluralistic Ignorance: Unveiling logical, rational, and epistemic components of an error phenomenon from social psychology.**

Date and time: Tuesday April 24, 2012 15:00-17:00

Location: Room A1.04, Science Park 904, Amsterdam

**Abstract : **Pluralistic ignorance in a phenomenon widely discussed in social psychology and related fields. In the literature, it is often portrayed as a cognitive error of social comparison, where individuals privately hold an opinion but mistakenly believe that others hold the opposite opinion. In most cases, people involved in pluralistic ignorance tend to act contrary to their private beliefs, but fail to realize that others may act insincere as well. Thus, pluralistic ignorance seems like a fail of rationality. However, I claim, there can be substantial amount of logic and epistemic rationality to pluralistic ignorance. Pluralistic ignorance may even arise among perfectly rational agents. In this talk, I will explicate the concept of pluralistic ignorance and explain why I claim that it can arise among rational agents. Furthermore, I will discuss initial attempts to use formal tools such as Dynamic Epistemic Logic (and maybe also game theory) to model the epistemic components of pluralistic ignorance.

**MARCH 27th 2012, SEMINAR MEETING (joint LogiCIC-LIRa seminar)**

Speaker: **Ondrej Majer **(Prague)

Title:** Substructural Epistemic Frames**

Date and time: Tuesday March 27 2012, 15:00-17:00

Location: Room D1.115, Science Park 904, Amsterdam

**Abstract : **The traditional way of representing knowledge in the framework of normal modal logics has been widely criticized, the most problematic property of this representation is logical omniscience (agents know all logical truths as well as all logical consequences of the facts they know). Many solutions of this problem have been proposed. Majer and Pelis [2] introduced a system employing relational semantics for distributive relevant logics which was further developed by Bilkova et al. [1]. This framework shares some intuitive features of modal representation, but is weak enough to avoid the logical omniscience and other criticized properties.

We shall present a generalization of this solution to weaker (but still distributive) substructural logics, demonstrate properties of the epistemic modality and discuss some other modalities, naturally accompaining the basic one. Our epistemic frames consist of information states -- collections of data represented as propostions -- which can be incomplete and/or contradictory. An agent in a given information state accepts a piece of data as knowledge only if it is confirmed by a source. The relation of 'being a source' can be defined in a very weak background logic (non-associative commutative Lambek calculs) so that the corresponding epistemic operator satisfies some minimal reasonable requirements for knowledge, but avoids the criticised properties of normal modal frames. The aim of this solution is not to search for a weakest framework possible but rather to propose a basic epistemic system to which we can add some stronger epistemic properties, if required by a particular application. Moreover some of the standard properties are characterized by conditions on the source relation.

[1] M.Bilkova, O.Majer, M.Pelis, and G.Restall. Relevant agents. In L.Beklemishev, V. Goranko, and V. Shehtman, editors, Advances in Modal Logic, pages 22--38. College Publications, 2010.

[2] O.Majer and M.Pelis. Epistemic Logic with Relevant Agents. In M.Pelis, editor, The {Logica} Yearbook 2008, pages 123--135. College Publications, 2009.

[3] G.Restall. An Introduction to Substructural Logics. Routledge, 2000.

**FEBRUARY 27th 2012, SEMINAR MEETING**

Speakers: **Maria Louisa Dalla Chiara** (Florence) and Roberto Giuntini (Cagliari)

Title: **From Quantum Information to Musical Semantics**

Date and time: Monday 27 February 2012, 16:00-18:00

Location: Room A1.10, Science Park 904, Amsterdam

**Abstract: **What link might connect two far worlds like quantum theory and music? There is something universal in the mathematical formalism of quantum theory that goes beyond the limits of its traditional physical applications. We are now beginning to understand how some mysterious quantum concepts, like superposition and entanglement, can be used as a semantic resource. Against the analytical tradition (inspired by classical logic) the semantics suggested by quantum information has reversed the relationship between whole and parts: it is the information about the whole that determines the information about the parts; and once broken into its parts, the puzzle cannot be reconstructed again! A particular form of quantum-like semantics can be successfully applied to a formal analysis of musical languages, where ambiguity, holism and contextuality play a relevant role.

**JANUARY 24th 2012, SEMINAR MEETING (two talks)**

Speakers: **Kevin T. Kelly **and** Hanti Lin** (Carnegie Mellon University)

Title: **Propositional Reasoning that Tracks Probabilistic Reasoning / Uncertain Acceptance and Contextual Dependence on Questions**

Date and time: Tuesday 24 January 2012, 16:00-18:00

Location: Room A1.10, Science Park 904, Amsterdam

**Abstracts**

Title: Propositional Reasoning that Tracks Probabilistic Reasoning

Abstract: This paper concerns the extent to which propositional reasoning can track probabilistic reasoning, which addresses kinematic problems that extend the familiar Lottery paradox. An acceptance rule (Leitgeb 2010) assigns to each Bayesian credal state p a propositional belief revision method B_p, which specifies an initial belief state B_p(\top), that is revised into the new propositional belief state B(E) upon receipt of information E. The acceptance rule *tracks* Bayesian conditioning when B_p(E) = B_p|_E(\top), for every E such that p(E) > 0; namely, when acceptance by propositional belief revision equals Bayesian conditioning followed by acceptance. Standard proposals for acceptance and belief revision do not track Bayesian conditioning. The ``Lockean'' rule that accepts propositions above a probability threshold is subject to the familiar lottery paradox (Kyburg 1961), and we show that it is also subject to new and more stubborn paradoxes when the tracking property is taken into account. Moreover, we show that the familiar AGM approach to belief revision (Harper 1975 and Alchourrón, Gärdenfors, and Makinson 1985) cannot be realized in a sensible way by an acceptance rule that tracks Bayesian conditioning. Finally, we present a plausible, alternative approach that tracks Bayesian conditioning and avoids all of the paradoxes. It combines an odds-based acceptance rule proposed originally by Levi (1996) with a non-AGM belief revision method proposed originally by Shoham (1987). As an application, the Lottery paradox turns out to receive a new solution motivated by dynamic concerns.

--

Title: Uncertain Acceptance and Contextual Dependence on Questions

Abstract: The preface paradox goes like this: an author may argue for a thesis in each chapter of her book, but in the preface she does not want to be committed to the conjunction of all theses, allowing for the possibility of error. The paradox illustrate a problem about acceptance of uncertain propositions across questions: for each chapter, there is the binary question whether its conclusion is correct; the preface asks a more complex question, namely, which theses are correct. The paradox is that asking for more can yield less. This paper addresses the extent to which acceptance of uncertain propositions depends on the question in context, by providing two impossibility results formulated in the following. Let uncertainty be modeled by subjective probability. Understand a *question* as having potential, complete answers that are mutually exclusive and jointly exhaustive; understand *answers* as disjunctions of complete answers. Assume that accepted answers within each question are closed under entailment. Assume, further, that acceptance is *sensible* in the sense that contradiction is never accepted, that answers of certainty are always accepted, and that every answer can be accepted without certainty. Then, as our first result, it is impossible that acceptance is *independent of questions*, namely, that if a proposition is accepted as an answer to a question, then it is accepted in every question to which it is an answer.

In light of the preceding result, one might settle on a weaker sense of question-independence. Say that a question is *refined* by another question if and only if each answer to the former question continues to be an answer to the latter question. As a weakening of question-independence, *refinement-monotonicity* requires that when an answer is accepted in a question, that answer is also accepted in every refined question. But refinement-monotonicity is too strong to be plausible, because, due to our second result, it is inconsistent with two intuitive principles for reasoning within each individual question. These two principles are: *cautious monotonicity* (i.e., do not retract accepted propositions when you learn what you already accept), and *case reasoning* (i.e., accept a proposition if it would be accepted no matter whether information E or its negation is learned), where information learning is assumed to follow the Bayesian ideal of conditioning.

Subpages (1): Slides of Valentin Goranko's tutorial "Logics for multi-agent systems"