The first meeting will take place on Monday, August 16, 2010. There will be 5 lectures of 90 minutes each. This website will have up-to-date information about the course (including slides and lecture notes). Please contact the instructor for more information.

Lecturers: Eric Pacuit ( website), Olivier Roy ( website)
Venue: European Summer School for Logic, Language and Information
(ESSLLI 2010)
Meeting Times: 11.00 - 12.30 (Day 1, Day 2, Day 3, Day 4, Day 5)
Location: University of Copenhagen, Denmark


Questions of collective agency and collective intentionality are not new in philosophy, but in recent years they have increasingly been investigated using logical methods. The work of Bacharach [2], Sugden [6] and Tuomela [7], in particular, elegantly combines philosophical relevancy with a strong inclination towards logical modeling of decision and action.

Logical and algebraic approaches are also more and more present in foundations of decision theory (cf. the work of Jeffrey [5] and Bradley [3]), epistemic game theory (Brandenburger [4] and van Benthem [8]), and, of course, dynamic epistemic logic [9,10]. These are three areas where questions of group agency and interaction also naturally arise. In these fields, however, group agency is rather studied from the perspective of individual decision makers, with the aim of understanding how the former stem from mutual expectations of the latter.

Little is known, however, about the relationship between these views on interaction and collective agency. On the one hand, decision- and game-theoretical approaches build on resolutely individualistic premises, and study the logic of individual belief and preferences in interactive decision making. On the other hand, the aforementioned philosophical theories take a more collectivist standpoint, focusing on how decision makers engage in “group”, “team” or “we-mode” of reasoning, which is often claimed to involve irreducibly collective attitudes.

This course will introduce these bodies of literature in order to clarify their relationship, both from a logical and a conceptual point of view. It will first cover recent development in the foundations of decision theory and epistemic foundations of equilibrium play in interaction. It will then move to the three philosophical theories of group agency mentioned above and, using logic as a common denominator, try to understand how they relate to decision- and game-theoretical approaches.

Reading Material

  • Extended outline of the course including an appendix on modal logic (pdf, June 15 version).

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Below is a schedule for the course (which is subject to change) with links to the lecture slides and brief synopses.

Date Topic Slides
Day 1
July 27, 2009
Introduction, Motivation and Background
(brief synopsis)
Lecture 1
Day 2
July 28, 2009
Alternative Approaches to Common Knowledge and Team Reasoning
(brief synopsis)
Lecture 2
Day 3
July 29, 2009
Variable Frame Theory and Epistemic Game Theory
(brief synopsis)
Lecture 3
Day 4
July 30, 2009
Epistemic Game Theory and Collective Rationality
(brief synopsis)
Lecture 4
Day 5
July 31, 2009
Collective Intentions
(brief synopsis)
Lecture 5

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Day 1: Introduction, Motivation and Background

Day 2: Alternative Approaches to Common Knowledge and Team Reasoning

Day 3: Variable Frame Theory and Epistemic Game Theory

Day 4: Epistemic Game Theory and Collective Rationality

Day 5: Collective Intentions


The course aims at students interested in theories of interaction, either from a philosophical or from more applied point of view (e.g. multi-agent systems). It will be for the most part self-contained, thus does not require previous knowledge of the philosophical or game- and decision-theoretical material that we will cover, but asks for a reasonable level of mathematical maturity. Consult the following papers and books for more information:

  1. R.J. Aumann and J.H. Dreze (2008). Rational expectations in games. American Economic Review, 98 (1): 72–86.
  2. M. Bacharach (2006). Beyond Individual Choices: Teams and Frames in Game Theory. Princeton University Press, Princeton, 2006. Edited by N. Gold and R. Sugden.
  3. R. Bradley (2007). A unified bayesian decision theory. Theory and Decision, 63 (3): 233–263.
  4. A. Brandenburger (2007). The power of paradox: some recent developments in interactive epistemology. International Journal of Game Theory, 35: 465–492.
  5. R. Jeffrey (1965). The Logic of Decision, McGraw-Hill, New-York, 1965.
  6. R. Sugden (2003). The logic of team reasoning. Philosophical Explanations 6, pages 165–181, 2003.
  7. R. Tuomela (1995). The Importance of Us: A Philosophical Study of Basic Social Notions, Stanford University Press, Stanford.<\li>
  8. J. van Benthem (2007). Rational dynamic and epistemic logic in games. International Game Theory Review, 9 (1): 13–45.
  9. J. van Benthem (forthcoming). Logical dynamics of information and interaction. Cambridge University Press.
  10. H. van Ditmarsch, W. van de Hoek, and B. Kooi. Dynamic Epistemic Logic, volume 337 of Synthese Library Series, Springer.

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Additional Information

Relevant Conferences: