Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Robert Mathews


Syllogisms having conclusions consistent with atmosphere are shown to be accepted at significantly higher rates than those having conclusions inconsistent with atmosphere. Furthermore, there is strong evidence that the dual influences of quality and quantity, independently affect acceptance rates. The first experiment also indicates a main effect of gender on acceptance rates to certain invalid syllogisms (those with conclusions inconsistent with quality, or quantity, or both). The second experiment replicates the atmosphere effect found in the first experiment and extends it to valid syllogisms and indeterminate invalids consistent with both quality and quantity. It also proposes an alternative to the misinterpreted necessity explanation for the logic by belief interaction. Both explanations are tested, and results indicate both are incomplete or incorrect. Evidence of a three way interaction of logic, belief, and consistency with atmosphere is reported. The third experiment tests the effect of instructions on response patterns. Instructions stressing correct logical procedures for judging validity fail to significantly improve performance or affect mean belief bias for either valid or invalid syllogisms. This experiment also indicates a main effect of gender on belief bias. The theoretical justification for an influence of consistency with atmosphere is proposed, as well as a model of syllogistic reasoning, which acknowledges the simultaneous influences of logic, believability, and consistency with atmosphere.