Hart\u27s Critics on Defeasible Concepts and Ascriptivism

Hart\u27s Ascription of Responsibility and Rights is where we find perhaps the first clear pronouncement of defeasibility and the technical introduction of the term. The paper has been criticised, disavowed, and never quite fully redeemed. Its lurid history is now being used as an excuse for dismissing the importance of defeasibility. Quite to the contrary, Hart\u27s introduction of defeasibility has uniformly been regarded as the most agreeable part of the paper. The critics\u27 wish that defeasibility could be better expounded along the lines of a Wittgensteinian game-theoretic semantics has largely been fulfilled. Even the most contentious part of the paper, Hart\u27s claim that the ascription of acts implies responsibility, is not as mistaken as some have taken it to be. The paper remains a paragon of clarity in the important and active scholarly area that crosses legal reasoning, language, and logic

Process and Policy: Resource-Bounded Non-Demonstrative Reasoning

This paper investigates the appropriateness of formal dialectics as a basis for non-monotonic and defeasible reasoning that takes computational limits seriously. Rules that can come into conflict should be regarded as policies, which are inputs to deliberative processes. Dialectical protocols are appropriate for such deliberations when resources are bounded and search is serial. AI, it is claimed here, is now perfectly positioned to correct many misconceptions about reasoning that have resulted from mathematical logic\u27s enormous success in this century: among them (1) that all reasons are demonstrative, (2) that rational belief is constrained, not constructed, (3) that process and disputation are not essential to reasoning. AI mainly provides new impetus to formalize that alternative (but older) conception of reasoning, and AI provides mechanisms with which to create compelling formalism that describes the control of processes. The technical contributions here are: the partial justification of dialectic based on controlling search; the observation that non-monotonic reasoning can be subsumed under certain kinds of dialectics; the portrayal of inference in knowledge based on policy reasoning; the review of logics of dialogue and proposed extensions; and the pre-formal and initial formal discussion of aspects and variations of dialectical systems with non-demonstrative reasons

Exact Dominance without Search in Decision Trees

In order to improve understanding of how planning and decision analysis relate, we propose a hybrid model containing concepts from both. This model is comparable to [Hartman90], with slightly more detail. Dominance is simple concept in decision theory. In a restricted version of our model, we give conditions under which dominance can be detected without search: that is, it can be used as a pruning strategy to avoid growing large trees. This investigation follows the lead of [Wellman87]. The conditions seem hard to meet, but may nevertheless be useful in forward-chaining situations without focus, such as [Breese87]. It may be possible to extend this work to produce better heuristic pruning based on inexact dominance and heuristic ability. Mainly, we contribute a detailed study of particular concept in a hybrid model that is the most detailed to date, further clarifying the relation between the two main paradigms for reasoning about preference among actions