Abstract

A classical approach to negation (e.g. Clark, 1974) maintains that its comprehension depends on the ability to detect differences between what is negated and the real state of affair. This view suggests that the more two things are different, the easier it is to perceive one of them as a valid negation of the other. However, a different view maintains that a negative sentence is plausible only if it negates a presupposition in the mind of the listener (Wason, 1965). This view suggests that the more two things are similar and liable to be confounded, the easier it is to perceive one of them as a valid negation of the other. Our four experiments, three of them based on conditional reasoning tasks, show that comprehending an item as the negation of another item is facilitated when the two items are similar. The effect is stronger in the comprehension of implicit negations (Experiment 1), but it is detectable also in the comprehension of explicit ones (Experiments 2, 3, 4). It cannot be entirely accounted for by mechanisms of information selection based on similarity cues nor by satisficing (Experiment 3). It is not originated by mechanisms of categorization, nor by carachteristics of conditional reasoning (experiment 4). The effect can be observed in primary school children (Experiment 4) as well as in adults. Our results support the notion that comprehension of negation, in a complex context, is based on the building of presuppositions about the factual ground of the negative statement.