Abduction and Question Answering

Abduction can be viewed as self-questioning, where the search for an explanation is analogous to answering a “why” question. The question is of the form Why P?, where P is an observation or fact that has come to an agent’s attention. An abductive hypothesis is a possible answer to the question Why P? When abduction is viewed as a type of question answering, abductive hypotheses can be seen as a subset of hypothetical (or conditional) answers. These answers are comprised of two components: a hypothesis that is consistent with an agent’s knowledge, but whose validity can not be determined, and an associated specific or generic answer, whose correctness hinges on the validity of the associated hypothesis. Hypothetical answering and abductive reasoning are both ways of coping with incomplete information. The difference between the two lies in the way in which the hypothetical information is employed. In abduction, a reasoner chooses to believe an abductive hypothesis based on factors such as belonging to a set of abducibles and informativeness. In question answering (excepting the case of self-questioning), the answering agent is reasoning in service of a distinct questioner, and has no reason to adopt or consider the hypothesis associated with a hypothetical answer as an update to its knowledge base. It is in the interest of an abductive reasoner to place higher value an abductive hypothesis that is more informative than other abductive hypotheses. This is true for the questioner also. The difference between abduction and question answering is that the answering agent does not customarily have access to the questioner’s knowledge base. This means that the informativeness of a hypothetical answer can not be determined by an answering agent, making it necessary to provide hypothetical answers at all possible levels of generality. It is generally not possible for the answering agent to measure the “informativeness” of an abductive hypothesis. This paper presents a discussion of the relationship between question answering and abduction.