People think about what is true for conditionals, not what is false: Only true possibilities prime the comprehension of “if”

Abstract

We report the results of two priming experiments that examine the comprehension of conditionals—for example, “if there are apples then there are oranges”—and biconditionals—for example, “if and only if there are apples then there are oranges”. The first experiment showed that participants read a biconditional faster when it was primed by a true possibility, “there were apples and there were oranges” than when it was primed by a false possibility, “there were no apples and there were oranges”; a conditional was primed equally by both possibilities. The second experiment showed that participants read the negated-antecedent conjunction faster when it was primed by a conditional than when it was primed by a biconditional; the affirmative conjunction was primed equally by both connectives. The experiments show that (a) when people understand “if A then B”, they access the true possibilities, “A and B”, and “not-A and B”, and (b) when they understand “if and only if A then B” they access “A and B”, but they do not access “not-A and B”. We discuss their implications for current theories of reasoning.

Keywords:

• Reasoning
• Conditional
• Biconditional
• Mental model theory
• Suppositional theory

This research has been supported by grant SEJ2006-14714 from the Spanish Ministry for Science and Technology.