Some Effects of Negation on Adults' Conditional Reasoning Abilities

Abstract

110 Ss evaluated conclusions for conditional reasoning arguments embodying 1 of 4 principles of inference: modus ponens, conversion, inversion, and modus tollens. The presence of the negative “not” was varied systematically within each major premise and conclusion. The results indicated that the form of the major premise had a significant ( p < .001) effect on reasoning. More importantly, it had a significant ( p < .001) differential effect according to the type of conclusion. The difference between Ss' mean error scores for conditional arguments with affirmative and negative conclusions was slight and nonsignificant ( p > .05).