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2nd Semester 2019/20: Non-Normal Epistemic Logics


Aybüke Özgün

If you are interested in this project, please contact  by email.

Registration until 31 May 2020


Epistemic logic is an umbrella term for a variety of modal logics whose main objects of study are  knowledge, belief,  and  related notions. These logics find applications not only in philosophy, but also in theoretical computer science, artificial intelligence, economics, and linguistics (for a survey  see Handbook of Epistemic Logic). Pioneered by Hintikka (1962), research in epistemic logic has widely advanced based on the formal ground of normal modal logics and standard possible worlds semantics on relational structures as they provide a relatively easy way of modeling knowledge and belief. However, as well known, this mainstream approach bakes in logical omniscience, modeling highly idealized reasoners who are far from having realistic cognitive powers and bounds. This has been seen as an increasingly serious limitation and led to the development of various non-normal epistemic logics for cognitively and computationally bounded agents. The relative merits and problems of such systems have yet to be fully assessed.

In this project, we focus on the problem of logical omniscience and investigate ways to strip well-known idealizations away from mainstream modal logics of knowledge and belief. We will survey at least the following approaches and their connections:

  • Neighbourhood Semantics for Epistemic Logic
  • Awareness Logics
  • Topic-Sensitive Epistemic Logics
  • Impossible Worlds Semantics

The detailed project syllabus will be published on the instructor's website and the lectures will be offered online.

If you have any questions about the course please contact the instructor via email:


There will be six 1.5-hour lectures in the first three weeks of June (1 hour lecture + 30 min discussion). On June 22nd, I will organize 15-30 min individual meetings with each student to discuss their final essay topics. 


Familiarity with basic modal logic, in particular, with its syntax, relational semantics, methods to prove expressivity and completeness results (students who have taken Introduction to Modal Logic or Dynamic Epistemic Logic should have the required background knowledge).


Pass/Fail based on:

  • Attendance and Class Participation 
  • Exercise Sets 
  • Final Essay


[1]  Berto, F. (2018) The theory of topic-sensitive intentional modals. The Logica Yearbook, forth- coming.

[2]  Berto, F. and Hawke, P. (2018) Knowability Relative to Information. Mind, forthcoming.

[3]  Berto, F. and Jago, M. (2018) Impossible Worlds. Stanford University Press.

[4]  Blackburn, P., de Rijke, M., and Venema, Y. (2001) Modal Logic. No. 53 in Cambridge Tracts in Theoretical Computer Science, Cambridge University Press, Cambridge, UK.

[5]  Chellas, B. F. (1980) Modal logic. Cambridge University Press, Cambridge.

[6]  Fagin, R., Halpern, J., Moses, Y., and Vardi, M. (1995) Reasoning about Knowledge. MIT Press, Cambridge, MA.

[7]  Fagin, R. and Halpern, J. Y. (1987) Belief, awareness, and limited reasoning. Artificial Intelligence, 34, 39 – 76.

[8]  Halpern, J. Y. and Pucella, R. (2011) Dealing with logical omniscience: Expressiveness and pragmatics. Artificial Intelligence, 175, 220 – 235, john McCarthy’s Legacy.

[9]  Hawke, P. (2018) Theories of aboutness. Australasian Journal of Philosophy, 96, 697–723.

[10]  Hawke, P., Özgün, A., and Berto, F. (2019) The fundamental problem of logical omniscience. Journal of Philosophical Logic, Forthcoming.

[11]  Hintikka, J. (1962) Knowledge and Belief. An Introduction to the Logic of the Two Notions. Cornell University Press, Ithaca, NY.

[12]  Hintikka, J. (1975) Impossible possible worlds vindicated. Journal of Philosophical Logic, 4, 475–484.

[13]  Konolige, K. (1986) What awareness isn’t: a sentential view of implicit and explicit belief. Halpern, J. Y. (ed.), Theoretical Aspects of Reasoning About Knowledge, pp. 241 – 250, Morgan Kaufmann.

[14]  Levesque, H. J. (1984) A logic of implicit and explicit belief. AAAI .

[15]  Pacuit, E. (2017) Neighbourhood Semantics for Modal Logic. Springer, Dordrecht.

[16]  Rantala, V. (1982) Impossible worlds semantics and logical omniscience. Acta Philosophica Fennica, 35, 18–24.

[17]  Rendsvig, R. and Symons, J. (2019) Epistemic logic. Zalta, E. N. (ed.), The Stanford Encyclo- pedia of Philosophy, Metaphysics Research Lab, Stanford University, summer 2019 edn.

[18]  Solaki, A. (2017) Steps out of Logical Omniscience. Master’s thesis, ILLC, University of Amsterdam.

[19]  Stalnaker, R. (1991) The problem of logical omniscience, i. Synthese, 89, 425–440.

[20]  van Ditmarsch, H., van der Hoek, W., Halpern, J., and Kooi, B. (eds.) (2015) Handbook of Epistemic Logic. College Publications.

[21] Velázquez-Quesada, F. R. (2014) Dynamic epistemic logic for implicit and explicit beliefs. Journal of Logic, Language and Information, 23, 107–140.

[22] Wansing, H. (1991) A general possible worlds framework for reasoning about knowledge and belief. Studia Logica, 50, 359.

[23] Yap, A. (2014) Idealization, epistemic logic, and epistemology. Synthese, 191.