Abstract

According to psychological theories dealing with propositional logic, conditional reasoning is a form of deductive reasoning. On the contrary, theories referring to Ramsey's suppositional interpretation posit that conditional statement (if p then q) is equivalent to the conditional probability of the consequent (q) given the antecedent (p) and that conditional reasoning is a form of probabilistic reasoning. This study compared the two competing hypotheses through an inference task where conditional syllogisms were presented with both premises (major premise «if p then not-q» and minor premises p, not-p not-q, q) or with minor premise only, and the conditional probability of «if p then not-q», the antecedent size and the consequent size were separately varied. In relation to Modus Ponens, results showed that, with the complete conditional syllogism, neither the conditional probability of «if p then not-q» nor the p and not-q size affected this inference. The theoretical implications are discussed in the text.