Effects of Negation on Adolescents' Class and Conditional Reasoning Abilities.

Sixty adolescents (30 boys and 30 girls) evaluated conclusions for deductive arguments embodying four principles of class reasoning and their logically equivalent isomorphs in conditional reasoning. The presence or absence of the negative "not" was varied systematically in the major premise of the arguments. The results indicated that (a) there was a lack of improvement during early adolescence in the ability to reason with both class and conditional reasoning arguments, (b) the difficulty of specific principles of inference varied according to both the type of reasoning and the location of negation in the major premise, and (c) while a negative in the first component (or both components) of the major premise of both class and conditional reasoning arguments generally reduced comprehension, a negative in only the second component had minimal effect.