Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The purpose of this thesis was to contrast two current theories of conditional reasoning. Conditional reasoning entails drawing inferences about situations in which the occurrence of one event is conditional upon the occurrence of another event (e.g., if the car runs out of gas, then it will stall). According to pragmatic schema theory (Cheng and Holyoak, 1985) conditional reasoning is mediated by context-sensitive inference rules that specify the inferences that are pragmatic in a given situation; these rules differ from context to context. For example, the inferences that are thought to be pragmatic in causal situations (in which one event causes another to occur) are thought to differ from permission contexts (in which one needs to satisfy a prerequisite in order to undertake a course of action). An alternative account is proposed in which inference patterns are determined by the perceived necessity and sufficiency of the conditional relationship. For example, necessary and sufficient rules ought to elicit different inferences than non-necessary and sufficient rules. Five experiments are reported which test predictions derived from these two theories. Experiments 1 and 2 established that the rated necessity of the conditional relationship was a better predictor than schema category of (a) the specific response patterns made by subjects on a conditional reasoning task and (b) the judged similarity of the "if then" and "only if" versions of a sentence. In Experiment 3, necessity and sufficiency ratings were gathered for a large pool of conditional statements. These ratings were used to select stimuli for Experiments 4 and 5 in which necessity, sufficiency, and schema category were varied orthogonally. The results of Experiments 4 and 5 demonstrated that necessity and sufficiency predicted performance on two different conditional reasoning tasks, whereas schema category did not. Taken together, these findings suggest that analysis in terms of necessity and sufficiency offers a useful framework both for classifying conditional sentences and for predicting reasoning performance, and further, that the concept of pragmatic schemas is unnecessary to account for the data.



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