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Department of Philosophy

Chair of Philosophy I – Prof. Dr. Olivier Roy

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We are studying questions of rationality in strategic interaction, learning and belief revision in social network, structure and justification of norms, and the philosophy of shared agency. For that we use methods from logic, computer science, and decision and game theory.

Rationality in Strategic Interaction

Why should players follow the recommendations of, say, Nash equilibrium or dominance reasoning in games? Traditional game theory leaves that question largely open. The epistemic view of games can be seen as an attempt at answering that question. The basic idea is to view rational decision making in games as not essentially different from rational decision making under uncertainty: it is a matter of coherence of choices and coherence of beliefs. With this in hand, one can look at what traditional, decision-theoretic norms would prescribe to players in games. When we do that it quickly becomes clear that higher-order beliefs (beliefs about beliefs) are central to the theory of rational decision making in strategic interaction, and that rationality in games is also a matter of rational belief revision. 

Deontic Logic and Permissions

The question of rationality in games raises important issues regarding the very logical structure of norms and their justification. Permissions are particularly interesting in from that point of view. It seems that in many contexts it makes more sense to talk about what is rationally permitted to do in games. Solution concepts rarely give unique prescriptions. To capture that we have been developing a new understanding of deontic modals, the logic of “obligations as weakest permissions,” and have been looking at the famous “Free Choice Permission” principle. This raises interesting question for deontic logic, action theory and defeasible reasoning.

Most of the current research on deontic logic at the Chair is currently done under the Permissions, Information and Institutional Dynamics, Obligations and Rights (PIOTR) project. This project is supported by the DFG-NCN (Poland) program "Beethoven". It studies the generation of obligations and duties from permissions and rights in deontic logic and law. The Principal Investigator is Prof. Dr. Olivier Roy. See the project website for more information.

Social Epistemology and Collective Action

Norms of rationality in strategic interaction often go hand-in-hand with collective decision-making demands. In social contexts, we can learn from, and have the possibility to act with others.  This can be a good thing, for instance when we get new evidence or achieve goals that we couldn’t reach alone. But this can also lead us astray, for instance in cases of polarization and pluralistic ignorance. We are currently looking at such phenomena using both analytical and simulation models, combining tools from logic, judgment aggregation and belief revision theory. See in particular Marcel Heidemann’s PhD project on that.

Most of the research on the topic at the Chair is currently done through three research projects:

  1. Collective Attitudes Formation (ColaForm) : This project is supported by the ANR-DFG (France) cooperation program. It studies how public deliberation and opinion pooling can be better aligned. The Principal Investigator is Prof. Dr. Olivier Roy. More information here.
  2. From Shared Evidence to Group Attitudes (SEGA) : This project is supported by the DFG-GACR (Czech Republic) cooperation program. It studies the relation between pooled and common attitudes in groups. The Principal Investigator is Prof. Dr. Olivier Roy. More information here.
  3. The Dynamics of Constructive Deliberation (DYCODE). This project is supported by the European Commission. Its aim is to study and develop formal models of the way individual agents and groups construct a collective decision problem. It is carried out by Dr. Frederik Van De Putte through his Marie Sklodowska-Curie Fellowship at the University of Bayreuth (Grant No. 795329), and supervised by Prof. Dr. Olivier Roy. More information here.

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