Probability logic and theModus Ponens—Modus Tollensasymmetry in conditional inference

Abstract

AbstractThis chapter focuses on the influence of pragmatic factors on reasoning — focusing on a prima facie puzzle for both logical and probabilistic accounts of reasoning: the asymmetry between modus ponens (MP) and modus tollens (MT) inferences in conditional reasoning. It discusses the account of the conditional developed by Adams. It shows that when applied to conditional inference, recent research in the normative literature (Sober, 2002; Sobel 2004; Wagner, 2004) is consistent with the account presented by Oaksford et al. (2000). These normative accounts introduce an important condition on probabilized MP and MT, called the rigidity condition which may explain the MP–MT asymmetry. It then argues that by exploiting this condition, far better fits to the data on conditional inference can be obtained.