Abstract :
Summary form only given, as follows. The study of how ordinary individuals reason shows that they do not make use of formal rules of inference. Instead, the evidence suggests that they imagine the states of affairs described in the premises, search for novel conclusions and, if they are reasonably prudent, submit these conclusions to test by further search for counterexamples. This method of reasoning is essentially semantic and it also calls upon any relevant general knowledge. The primary goal is to reach a true conclusion, rather than to reach a necessarily true conclusion. However, ordinary individuals are aware of what it is for a conclusion to be necessarily true and in the psychological laboratory show some competence to infer such conclusions
