The mental logic theory of conditional propositions
David O’Brien, Andrea Manfrinati · Oxford University Press eBooks · 2010
This chapter makes the case for the existence of various formal syntactic inference schemata in the human cognitive system. These inferential schemata must be applied to incoming verbal information in working memory to draw conditional inferences. It argues that our evolved mental logic is not the same as standard textbook logic in which ex falso quodlibet holds, i.e., anything follows from a contradiction. In mental logic, reaching a contradiction just indicates something has gone wrong in the chain of reasoning and that therefore a premise needs to be rejected, as in reductio ad absurdum reasoning. Thus, the response to the problem of defeasiblity is that, e.g., on reaching a contradiction by having inferred Tweety can fly and then discovering that Tweety is an Ostrich one must reject the original conditional, birds fly (if x is a bird, then x flies). The chapter also shows that logical inferences are always made in the context of other pragmatic inferences. It outlines the evidential support for the existence of inferential schemata and then examines the ability of other accounts of conditional reasoning to explain these results and finds them wanting.