Disjunction of natural concepts

Two experiments investigated the way in which the rated membership of items in disjunctively defined categories, such as FRUITS OR VEGETABLES and PETS OR FARMYARD ANIMALS, varies as a function of membership in individual constituent categories. Items were rated for category membership and typicality in each category separately, and in their disjunction. The results showed non-Boolean effects of both overextension and underextension of the disjunctions. Typicality in the disjunction was highly predictable from constituent typicality values, using regression equations with negative interaction terms. The results are compared with similar effects for concept conjunctions and are discussed in terms of an intensional model of conceptual combination (Hampton, 1987b, 1988).