Safety Logics

In this paper we begin the analysis and formalisation of common sense reasoning about safety. To begin with we analyse absolute safety, and use and extend the framework of Dynamic Logic in order to develop a formal possible-worlds semantics and logic for it. We then extend the analysis to normal safety. We introduce Defeasible Dynamic Logic in order to give possible-worlds semantics and logic for normal safety, and define a preferential entailment relation defined in order to represent common sense reasoning about the normal termination of actions. We conclude with a discussion of the relationship between safety, obligation, rationality and risk, and outline some extensions to the present work.