The influence of verbal mood in exceptive conditional reasoning: indicative versus subjunctive

Abstract

Background: We report the results of two experiments that examine the mental representations underlying the comprehension and reasoning stages of negative exceptive conditionals requiring the subjunctive ('B a menos que A' and 'B a no ser que A' = 'B unless A') and the indicative mood ('B excepto si A' and 'B salvo si A' = 'B except if A'). Method: A truth table task was employed to infer the mental representation that people have in mind when they reason with negative exceptive conditionals. Results: Both experiments showed that participants selected the possibility 'B & not-A' more frequently than the possibility 'not-B & A' when the conditional required the indicative mood, but they selected the possibilities 'B & not-A' and 'not-B & A' equally frequently when the conditional required the subjunctive mood. Conclusions: Exceptive conditionals in the subjunctive mood lead people to think in terms of dual possibilities, whereas the indicative mood leads people to consider just one possibility.