Two complementary sets of experiments were carried out to investigate how people understand, and reason with, truth-functional conditional forms. The first four experiments employed abstract materials and sought primarily to investigate the notion that people interpret conditionals like ‘if P then Q’ a ‘fuzzy’ way – that is, as if such a statement means something like ‘if P then, generally speaking, Q’. Evidence was found that people will tolerate, or even expect, a certain degree of fuzziness in a conditional scenario such that they will be prepared to rate such a conditional statement as true despite the existence of a (small) proportion of falsifying counterexamples. Systemic effects of various extra-logical factors such as syntactic form and availability were also identified, and these were shown to be at their strongest when features of the reasoning task rendered it more difficult to perform.

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