Expertise and information: an epistemic logic perspective

In this paper we present a modal logic framework to reason about the expertise of information sources. A source is considered an expert on a proposition ? if they are able to correctly refute phi in any possible world where phi is false. Closely connected with expertise is a notion of soundness of information: phi is said to be "sound" if it is true up to lack of expertise of the source. That is, any statement logically weaker than phi on which the source has expertise must in fact be true. This is relevant for modelling situations in which sources make claims beyond their domain of expertise. Particular attention is paid to the connection between expertise and knowledge: we show that expertise and soundness admit precise interpretations in terms of S4 and S5 epistemic logic, under certain conditions. We go on to extend the framework to multiple sources, defining two notions of collective expertise. These also have epistemic interpretations via distributed and common knowledge from multi-agent epistemic logic. On the technical side, we give several sound and complete axiomatisations of various classes of expertise models.