When negation is easier than affirmation

An experiment is reported which establishes that affirmative sentences are not always easier to grasp than negative sentences. The subjects had to make inferences from pairs of premises such as: “Either John is intelligent or he is rich. John is not rich”. The task was reliably easier when the second premise was explicitly negative (as in the example) than when it was an affirmative (“John is poor”). It was most difficult when the negative occurred in the disjunctive premise and was denied by an affirmative (e.g. “John is intelligent or he is not rich. John is rich”). It is argued that it is simpler to establish that two statements are mutually inconsistent when one is the explicit negation of the other, but that the natural function of the negative is to deny.