A Logic of Plausible Justifications

In this work, we combine the frameworks of Justification Logics and Logics of Plausibility-Based Beliefs to build a logic for Multi-Agent Systems where each agent can explicitly state his justification for believing in a given sentence. Our logic is a normal modal logic based on the standard Kripke semantics, where we provide a semantic definition for the evidence terms and define the notion of plausible evidence for an agent, based on plausibility relations in the model. This way, unlike traditional Justification Logics, justifications can be actually faulty and unreliable. In our logic, agents can disagree not only over whether a sentence is true or false, but also on whether some evidence is a valid justification for a sentence or not. After defining our logic and its semantics, we provide a strongly complete axiomatic system for it and show that it has the finite model property and is decidable. Thus, this logic seems to be a good first step for the development of a dynamic logic that can model the processes of argumentation and debate in multi-agent systems.