A proposal for fuzzy International Union for the Conservation of Nature (IUCN) categories and criteria

The classification of endangered species uses categories "extinct in the wild", "endangered" and so on that are intrinsically vague. This vagueness presents various problems for those trying to classify species. The usual way of dealing with this vagueness is to eliminate it by providing precise definitions of the categories in question. In this paper we propose a fuzzy set-theoretic alternative that respects the inherent vagueness of the crucial categories without compromising the utility of the classification scheme. Moreover, we argue that it leads to intuitively more appropriate classifications in many cases. (C) 1999 Elsevier Science Ltd. All rights reserved.