Conditional Reasoning Part I

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Abstract Three types of conditional are distinguished: the material conditional, indicative conditional, and subjunctive/counterfactual conditional. The apparent difference in truth conditions of each is suggestive of different psychological procedures used in the evaluation of each. The psychology of the material conditional is then examined. Despite procedures in formal logic that are suggestive of sui generis imaginative states (e.g., “assuming” a proposition for conditional proof, or for reductio), we need not countenance the use of such states within the psychological procedures used to carry out the inferences. Further, work in psychology has long suggested that humans do not, as a rule, reason in accordance with normative standards appropriate to the material conditional. A popular alternative proposal in psychology is that conditional reasoning involves the use of mental models (Johnson-Laird & Byrne, 2002). The use of mental models is shown to be consistent with conditional reasoning involving only sequences of beliefs.