Are conjunctive inferences easier than disjunctive inferences? A comparison of rules and models

We report four experiments investigating conjunctive inferences (from a con junction and two conditional premises) and disjunctive inferences (from a d isjunction and the same two conditionals). The mental model theory predicts that the conjunctive inferences, which require one model, should be easier than the disjunctive inferences, which require multiple models. Formal rul e theories predict either the opposite result or no difference between the inferences. The experiments showed that the inferences were equally easy wh en the participants evaluated given conclusions, but that the conjunctive i nferences were easier than the disjunctive inferences (1) when the particip ants drew their own conclusions, (2) when the conjunction and disjunction c ame last in the premises, (3) in the time the participants spent reading th e premises and in responding to given conclusions, and (4) in their ratings of the difficulty of the inferences. The results support the model theory and demonstrate the importance of reasoners' inferential strategies.