ABSTRACT
INTRODUCTION In Chapters 4 and 5, we examined the consequences for logicist cognitive science of the defeasibility of everyday reasoning. We also considered a wide variety of potential solutions to the problem of defeasibility that have been proposed within the cognitive sciences, arguing that these were not successful. These included mental models theory, which forms one of a small set of highly influential theories that have been proposed within cognitive psychology to account for experimental evidence concerning human deductive reasoning. In this chapter, we consider more generally the extent to which psychological theories developed to account for human deductive reasoning can generalise to everyday defeasible reasoning. We argue that it is crucial that such theories do generalise to everyday defeasible inference, because, outside mathematical domains, deductive reasoning appears to find little application. This is because people need to reason about a world that is uncertain, and that does not admit of exceptionless generalisations, as argued in Chapter 4. So if psychological theories of reasoning apply only to deduction, then, as we remark in this chapter, they may be of no more interest than, say, the psychology of playing monopoly.
