Prototype theory is reviewed from three perspectives: comparison of the theory with the traditional view of semantic categories and the theory of fuzziness; application of the concept of prototype in various domains of linguistic description; and functional analysis of the role of prototype categories in human cognition. It is shown that the theory is explanatorily more powerful in two respects: it can resolve the problem of illogicality inherent in the traditional view in explaining deduction and induction, and it can account for such forms of reasoning as metaphor that involves two semantic categories. (LLBA, Adapted from the source document, Accession Number 9906112, (c) CSA [1998]. All rights reserved.)