OSCAR--A General-Purpose Defeasible Reasoner

In its present incarnation, OSCAR is a fully implemented programmable architecture for a rational agent. This architecture is described in detail in a forthcoming book entitled Cognitive Carpentry. It is an important characteristic of OSCAR that most practical reasoning is reduced to epistemic reasoning, through a process I call "doxastification’. In particular, most (but not quite all) of the details of planning, plan adoption, and plan execution are carried out by epistemic reasoning. If we focus just upon the epistemic reasoning in OSCAR, what we have is a powerful general-purpose defeasible reasoner. The purpose of this paper is to describe that reasoner. OSCAR’s defeasible reasoner is based upon seven fundamental ideas. These are (1) an argument-based account of defeasible reasoning, (2) an analysis of defeatstatus given a set of interrelated arguments, (3) the proposal of a general adequacy criterion for automated defeasible reasoners, called "i.d.e.-adequacy’, (4) the claim that general-purpose defeasible reasoner must have the kind of structure I have called "flag-based", (5) an algorithm for computing defeat-status, (6) an interest-driven monotonic reasoner, and (7) an account of degrees justification, degrees of interest, and their interactions.