**PI:**

**Dr. Dr. Niki Pfeifer**

**Institution:**Ludwig-Maximilians-Universität München

**Abstract**

This project is located in the intersection of formal epistemology and the new paradigm psychology of reasoning. It will further develop "coherence based probability logic" (CPL) as a new rationality framework for formal and empirical studies on reasoning under uncertainty. In the coherence framework, probabilities are conceived as subjective degrees of belief and conditional probability is defined as a primitive concept. The coherence approach is especially suitable for dealing with zero antecedent probabilities.

Three working packages (WP1-WP3) shall be accomplished to establish new answers to the following key questions of the SPP1516: How useful are qualitative (logic-based) and quantitative (probability-based) approaches for modeling human thinking? What is rationality under uncertainty? In WP1, we will develop a coherence-based probability semantics for categorical syllogisms. Philosophically, we will develop new probabilistic interpretations of central syllogistic concepts (like quantifiers, existential import, the square of opposition). Psychologically, we will run experiments on the new semantics. The psychological plausibility will be empirically investigated. The new semantics will be critically discussed in the light of current psychological theories of categorical syllogisms.

In WP2, we will philosophically analyze various rationality principles of nonmonotonic conditional logics in their qualitative and quantitative versions within the framework of CPL. Furthermore, we will test experimentally which of the rationality principles are actually endorsed by people, and hence which system explains best how people reason under incomplete probabilistic knowledge.

In WP3, we will develop a philosophical account of iterated conditionals and test the empirical adequacy of our theory in a series of experiments. In particular, we will study, both theoretically and experimentally, the relationship between learning a conditional information, which is associated with interpreting left-nested conditionals, and explanatory reasoning. Additionally—in the context of right-nested conditionals—we will investigate the psychological plausibility of the Import-Export Principle, which is frequently assumed by philosophers, yet it does not hold in CPL.

The ultimate (bold) goal is to develop CPL as an unified rationality framework for uncertain reasoning and to construct Mental Probability Logic as a philosophically informed and descriptively adequate competence theory of human uncertain inference. WP1-WP3 describe important steps towards this goal.

Projekt-Homepage: http://www.pfeifer-research.de/spp.html

**Project-related Publications**

Pfeifer, N. (2016). Experimental probabilistic pragmatics beyond Bayes' theorem.

*Zeitschrift für Sprachwissenschaft, 35*(1), 89-96.

Gilio, A., Pfeifer, N., & Sanfilippo, G. (2016). Transitivity in coherence-based probability logic.

*Journal of Applied Logic, 14*, 46-64.

Pfeifer, N. (2014). Reasoning about uncertain conditionals.

*Studia Logica,*

*102*, 849-866.

*More publications can be found on this page.*

**Relation to the SPP1516's first funding period**

Project "Rational reasoning with conditionals and probabilities - Logical foundations and empirical evaluation" (Kern-Isberner/Pfeifer)