January 13 – 16 , 2019, Dagstuhl Seminar 19032

Conditional Logics and Conditional Reasoning: New Joint Perspectives


Guillaume Aucher (University of Rennes 1 & IRISA Rennes, FR)
Paul Egré (ENS – Paris, FR)
Gabriele Kern-Isberner (TU Dortmund, DE)
Francesca Poggiolesi (CNRS – Paris, FR)

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Annette Beyer for administrative matters

Shida Kunz for scientific matters


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Logic in the first half of the 20th century has been mostly concerned with mathematical reasoning and providing a unified framework for the foundations of mathematics. In the second half of the 20th century, with the emergence of artificial intelligence, new formalisms have been introduced to model kinds of inference closer to everyday life.

"Commonsense reasoning", the reasoning that humans perform in everyday life, is significantly different from the reasoning of mathematicians, which has been the object of study of (mathematical) logic for a long time. It is very rich and includes different kinds of reasoning, such as counterfactual reasoning, default reasoning or uncertain and plausible reasoning. Commonsense reasoning is often captured by means of conditionals, which are sentences of the form ‘if A then B’. These conditionals can also be of various kinds: counterfactual, indicative, or subjunctive. The benefits of conditionals for formalizing commonsense reasoning are basically twofold: first, they can encode reasoning patterns of various types if one chooses suitable semantics or calculi, and second, they provide a common syntactic element that can be used to relate and compare the different kinds of commonsense reasoning as well as the mathematical reasoning.

Over the last decades, a number of mathematical advances have been made in modal logic, an area closely related to conditional logics. However, the techniques developed in modal logic with respect to proof theory and correspondence theory have not fully been applied to the conditional logics introduced in artificial intelligence and philosophy. The first objective of this Dagstuhl Seminar is to get together logicians and formal semanticists interested in commonsense reasoning in order to provide solid foundations and revisit conditional logics in light of these recent mathematical advances. Conditionals are also studied in the psychology of reasoning, which has recently witnessed a new wave work. In particular, an effort to confront semantic frameworks with empirical results has been made. The second objective of this seminar is to provide an opportunity for these different communities to meet and reinforce their ties.

  Creative Commons BY 3.0 DE
  Guillaume Aucher, Paul Egré, Gabriele Kern-Isberner, and Francesca Poggiolesi


  • Artificial Intelligence / Robotics
  • Verification / Logic


  • Conditionals
  • Psychology of reasoning
  • Commonsense Reasoning
  • Proof theory
  • Correspondence theory

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