A Formal Explication of the Search for Expla- nations The Adaptive Logics Approach to Abductive Reasoning

Summary. Most logic–based approaches characterize abduction as a kind of back-wards deduction plus additional conditions, which means that a number of conditions is specified that enable one to decide whether or not a particular abductive inference is sound (one of those conditions may for example be that abductive consequences have to be compatible with the background theory). Despite the fact that these approaches succeed in specifying which formulas count as valid consequences of abductive inference steps, they do not explicate the way people actually reason by means of abductive inferences. This is most clearly shown by the absence of a decent proof theory. Instead, search procedures are provided that enable one to determine the right abductive consequences. However, these do not by far resemble human reasoning. In order to explicate abductive reasoning more realistically, an alternative approach will be provided in this paper, viz. one that is based on the adaptive logics programme. Proof theoretically, this approach interprets the argumentation schema affirming the consequent (AC: A ⊃ B,B ` A) as a defeasible rule of inference. Thi