Logical dynamics of evidence

Evidence is the underpinning of beliefs and knowledge. Modeling evidence for an agent requires a more fine-grained semantics than possible worlds models. We do this in the form of "neighbourhood models", originally proposed for weak modal logics. We show how these models support natural actions of "evidence management", ranging from update with external new information to internal rearrangement. This perspective leads to richer languages for neighborhood semantics, including modalities for new kinds of conditional evidence and conditional belief. Using these, we indicate how one can obtain relative completeness theorems for the dynamic logic of evidence-changing actions.