PROBLEM DIFFICULTY AND RESPONSE FORMAT IN SYLLOGISTIC REASONING

It was hypothesized that the perceived irrelevance of the proposition ''Some X are not Y'' is a factor contributing to the difficulty of nea rly all the determinate syllogisms classed as multiple model by Johnso n-Laird and Byrne (1991), according to mental models theory. Experimen t 1 supported this hypothesis by showing that subjects frequently corr ectly evaluate valid ''Some...not'' conclusions but rarely produce the m, even when they have evaluated them elsewhere. Explanations of these findings based on the use of superficial strategies were ruled out. E xperiment 2 further supported the hypothesis by showing that performan ce increased across the no-conclusion, multiple-choice, and evaluation task formats, and that this effect generalized to problems containing the quantifier ''only''. However, the initial hypothesis was rejected in light of Experiment 3, which found no difference between multiple- choice and no-conclusion formats when the number of allowable conclusi ons was controlled for. Nevertheless, superior performance remained in the evaluation format, and it is suggested that offered conclusions m ay be used as a goal for the reasoning process. This interpretation is supported by the finding (Experiments 1 and 3) that subjects appear t o search only for alternative conclusions that maintain the subject-pr edicate structure of the offered conclusion.