Two varieties of conditionals and two kinds of defeaters help reveal two fundamental types of reasoning

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.