Dear all,

Tomorrow at 16:30 we will have a joint LLAMA and LIRa session!

This will be a *hybrid* session. If you want to attend online, please use the following ZOOM LINK, DIFFERENT THAN OUR USUAL ONE: https://uva-live.zoom.us/j/84413536364 Meeting ID: 844-1353-6364

You can find the details of the talk below.

This will be a joint session together with the LLAMA seminar.

Speakers: Ekaterina Kubyshkina & Mattia Petrolo

Date and Time: Thursday, April 20th 2023, 16:30-18:00

Venue: ILLC seminar room F1.15 in Science Park 107 and online.

Title: Creating new worlds: a PAL for excusable ignorance.

Abstract. There is a lively debate in the current literature on epistemology on which type of ignorance may provide a moral excuse. A good candidate is the one in which an agent has never thought about or considered as true a proposition p. From a logical perspective, no formal analysis was provided for ignorance as an excuse. We fill this gap by providing an original logical setting for modelling this type of ignorance. In particular, we introduce a complete and sound logic in which ignorance is expressed as a primitive modality. Semantically, the logic is characterized by Kripke semantics with possibly incomplete worlds, or, equivalently, Kripke models equipped with a three-valued valuation function. Moreover, to consider the conditions of a possible change of an agent's ignorance, we will extend the setting to public announcement logic. First, we show that standard update procedures are not suitable for an adequate representation of scenarios involving excusable ignorance. Secondly, we define an original update procedure, which modifies the initial models by creating new worlds and accessibilities, instead of eliminating them. We exemplify the fruitfulness of this procedure via an intuitive example.

(joint work with M. K. Pereira)

Hope to see you there!

The LIRa team