Interpretation of Conditionals in the Suppression Task

If people are presented with a conditional sentence and a corresponding categorical premise, they easily make modus ponens inferences. But several studies have shown that this valid inference of classical logic can be suppressed by adding another conditional sentence containing an additional necessary condition. Although most authors accounting for this suppression of inferences have stressed the importance of interpretative processes, it has not been investigated sufficiently how subjects really interpret such conditional sentences in practice. Thus, this dissertation examines people’s interpretations in interviews, utilising statements similar to those used in previous studies. The results indicate that there is a wider range of possible interpretations than assumed in accounts of the suppression effect in the literature, and that subjects do not always adopt the interpretations expected by experimenters. Moreover, they show that there is often no clear-cut distinction between interpretation and reasoning. This study investigates the influence of other factors like participants’ understanding of the task, character or the use of world knowledge. It also examines the role of background or abnormality conditions and counterexamples for the meaning of conditionals. The findings are used to assess other ways of accounting for the suppression effect and conditional reasoning in general, like the theory of mental models or probabilistic approaches.