Dynamics of Defeasible and Tentative Inference

Standard refinements of epistemic and doxastic logics that avoid the problems of logical and deductive omniscience cannot easily be generalised to default reasoning. This is even more so when defeasible reasoning is understood as tentative reasoning; an understanding that is inspired by the dynamic proofs of adaptive logic. In the present paper we extend the abnormality (preference) models for adaptive consequence with a set of open worlds to account for this type of inferential dynamics. In doing so, we argue that unlike for mere deductive reasoning, tentative inference cannot be modelled without such open worlds.