In this talk I will explore the thesis that the role of argumentation in practical reasoning is to justify the use of defeasible rules to derive a conclusion in preference to other defeasible rules to derive a conflicting conclusion. The defeasibility of rules is expressed by means of non-provability claims as additional conditions of the rules.
I will outline an abstract approach to defeasible reasoning and argumentation which includes many existing formalisms, i.e. Theorist (abduction), circumscription, default logic, extended logic programming, non-monotonic modal logic(s) and auto-epistemic logic, as special cases. I will present an argumentation semantics (the `admissibility'' semantics) for defeasible reasoning that is more liberal than the standard semantics of the existing formalisms. In the admissibility semantics there is only one way for one argument to ``attack'' another, namely by undermining one of its non-provability claims. If time allows, I will argue that other kinds of attack between arguments, specifically rebuttal and priority attacks, can be reduced to undermining non-provability claims. Bibliography A. Bondarenko, P.M. Dung, R.A. Kowalski, F. Toni ``An abstract, argumentation-theoretic approach to default reasoning'' To appear in Artificial Intelligence R.A. Kowalski, F. Toni, ``Abstract Argumentation'' Artificial Intelligence and Law 4(3--4) (1996) Special Issue on Logical Models of Argumentation Contact Information Francesca Toni Imperial College, Department of Computing 180 Queen's Gate, London SW7 2BZ, UK Tel: +44 171 594 8228 Fax: +44 171 589 1552 Email: ft@doc.ic.ac.uk Web: http://laotzu.doc.ic.ac.uk/UserPages/staff/ft/ft.html