Conceptual illusions.

Many concepts depend on negation and on relations such as conjunction and disjunction, as in the concept: rich or not democratic. This article reports studies that elucidate the mental representation of such concepts from descriptions of them. It proposes a theory based on mental models, which represent only instances of a concept, and for each instance only those properties, affirmative or negative, that the description asserts as holding in the instance. This representation lightens the demands on working memory, but it also leads to predictable conceptual 'illusions' in which individuals envisage as instances of a concept some cases that in fact are non-instances, and vice versa. Experiments 1 and 2 demonstrated the occurrence of these illusions. Experiment 3 corroborated their results, and showed that the illusions can be alleviated in a predictable way by predicates with certain meanings. These findings cannot be easily explained by alternative theories.