Two Varieties of Conditionals and Two Kinds of Defeaters Help Reveal Two Fundamental Types of Reasoning


  • The authors are grateful to Didier Dubois for helpful technical suggestions.

Guy Politzer, CNRS, Institut Jean-Nicod, 1 bis avenue Lowendal, 75007, Paris, France; Jean-François Bonnefon, Laboratoire Travaile et Cognition, University of Toulouse, Maison de la Recherche, 5 allées Antonio Machado 31038, Toulouse, France.


Abstract:  Two notions from philosophical logic and linguistics are brought together and applied to the psychological study of defeasible conditional reasoning. The distinction between disabling conditions and alternative causes is shown to be a special case of Pollock’s (1987) distinction between ‘rebutting’ and ‘undercutting’ defeaters. ‘Inferential’ conditionals are shown to come in two varieties, one that is sensitive to rebutters, the other to undercutters. It is thus predicted and demonstrated in two experiments that the type of inferential conditional used as the major premise of conditional arguments can reverse the heretofore classic, distinctive effects of defeaters.