The psychology of inferring conditionals from disjunctions: A probabilistic study

There is a new probabilistic paradigm in the psychology of reasoning that is, in part, based on results showing that people judge the probability of the natural language conditional, if A then B, P(if A then B), to be the conditional probability, P(B vertical bar A). We apply this new approach to the study of a very common inference form in ordinary reasoning: inferring the conditional if not-A then B from the disjunction A or B. We show how this inference can be strong, with P(if not-A then B) "close to" P(A or 8), when A or B is non-constructively justified. When A or B is constructively justified, the inference can be very weak. We also define suitable measures of "closeness" and "constructivity", by providing a probabilistic analysis of these notions. (C) 2012 Elsevier Inc. All rights reserved.