Is the logical equivalence between conditional and disjunction also a psychological equivalence?  

Manfrinati A., Tasso A., Cherubini P., Giaretta P., Altoè G.
First author's affiliation: University of Valle d'Aosta, Venezia, Italy

One of the main problems that a theory of conditionals has to deal with is that some conditionals are well understood by people in everyday reasoning, even if they seem partially undefined as they lack truth value when the antecedent is false. The aim of this study was to investigate the following hypothesis: explicit disjunctive information affects the extent to which related conditionals are perceived as defined in different situations. Participants (N=39) evaluated meaning equivalence of conditional and disjunctive sentences using a 5-point scale ranging from 1 (different meaning) to 5 (same meaning). The independent variables were: type of conditional (conditional vs. biconditional); content (concrete vs. abstract); order of presentation (disjunction first vs. conditional first); polarity (conditional with a negated antecedent vs. disjunction with a negated term). Statistical analysis showed that equivalence evaluation is affected by content (p < .001), polarity (p < .001) and, more interestingly, by order of presentation (p = .026) - a disjunction seems to involve a conditional but not vice versa. This study provides evidence for the idea that mental representation (or mental model) of the disjunction could make it easier to form the mental representation (or mental model) of the conditional.