REASONING WITH NEGATIVES
J. St B. T. Evans · British Journal of Psychology · 1972
Two experiments are reported on the effect of negation on reasoning with conditional rules. In Expt. I significantly more affirmative than negative statements were denied by a valid inference ( modus tollens ), and significantly more negative than affirmative statements were affirmed by a fallacious inference ( affirmation of the consequent ). Subjects made their inferences by choosing from a list of possible conclusions, so that, for example, an affirmative statement, p , could be denied by selecting the negative conclusion, not p. It was hypothesized that the greater difficulty experienced by subjects in the denial of not p by a choice of p might be due to the additional intermediate step of double negation. i.e. not not p , which is involved. The results of Expt. II suggested, however, that the difficulty lies in subjects' inability to infer that a negative statement is false, rather than in the process of transforming a double negative into an affirmative.