Speaker: Stipe Pandžić (Utrecht University)
Date and Time: Thursday, March 10th 2022, 16:30-18:00, Amsterdam time.
Venue: online. Recording available, click here.
Title: Default justification logic as a theory of arguments and epistemic justification.
Abstract. My goal in this talk is to present a logic of structured defeasible argumentation using the language of justification logic. One of the key features that is absent in standard justification logics is the possibility to weigh different epistemic reasons that might conflict with one another. To amend this, we develop a semantics for “defeaters”: conflicting reasons forming a basis to doubt the original conclusion or to believe an opposite statement. Formally, non-monotonicity of defeasible reasons is introduced through default rules with justification logic formulas.
Default justification logic is unique for its ability to represent defeasible arguments as object-level formulas. Sets of such formulas are then interpreted with an acceptance semantics, in analogy to Dung’s abstract argumentation framework semantics. In contrast to argumentation frameworks, determining arguments’ acceptance in default justification logic simply turns into finding (non-monotonic) logical consequences from a starting theory with justification assertions. We can show that a large subclass of Dung’s frameworks is a special case of default justification logic. By the end of this talk, I will connect this logic of arguments with the epistemological debate on justified-true-belief definition of knowledge.