Chapter

Variable priorities and exclusion

John F. Horty

in Reasons as Defaults

Published in print April 2012 | ISBN: 9780199744077
Published online September 2012 | e-ISBN: 9780199932566 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199744077.003.0005
Variable priorities and exclusion

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This chapter considers two ways in which the simple default logic defined earlier can be elaborated, leading to a more robust theory of reasons. First, the priorities among default rules have so far been taken as fixed in advance, but there are situations in which it is most natural to think of these priorities themselves as established through default reasoning. And second, the notion of defeat defined so far captures only one form, described here simply as “defeat,” but often called “rebutting defeat.” There is at least one other form, generally called “undercutting defeat,” and related to the concept of an “exclusionary reason,” in which one default defeats another, not by contradicting its conclusion, but by undermining its capacity to provide a reason at all.

Keywords: variable priorities; undercutting defeat; exclusionary reasons; intensifiers; attenuators

Chapter.  18451 words.  Illustrated.

Subjects: Philosophy of Mathematics and Logic

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