A logic of default justifications

We define a logic of default justifications that relies on operational semantics. One of the key features that is absent in standard justification logics is the possibility to weigh different epistemic reasons or pieces of evidence that might conflict with one another. To amend this inadequacy, we develop a semantics for “defeaters”: conflicting reasons forming a basis to doubt the original conclusion or to believe an opposite statement. Our logic is able to address interactions of normal defaults without relying on priorities among default rules and introduces the possibility of extension revision for normal default theories