Abduction is not Deduction-in-Reverse.

Abduction is a topic that attracts much interest in AI and automated reasoning research. Different approaches have been devised, that give a formalized account of explanatory reasoning, propose methods to compute explanations, frame abduction in the context of logic programming. However, the logical nature of abduction is still far from being clear and different specifications of the key underlying concepts have been given, that make it difficult to speak of abduction as a single well-defined form of reasoning. This work is a preliminary discussion on the logical nature of abductive reasoning, emphasizing the fundamental difference between abductive and deductive inference. Some logical properties of the inference to the "best explanation" are put forward and analyzed when the underlying logic is any extension of classical propositional logic (first order logic, modal logic) or a non monotonic system.