## Fundamental Postulate

KELLY'S PERSONAL CONSTRUCT THEORY.

FUZZY SET/LOGIC THEORY. Fuzzy set/logic theory refers to a generalized concept of a logical set in which the elements have continuously graded degrees of set membership that range from the values 0 to 1 (rather than either belonging or not belonging to the set as in conventional set theory). Fuzzy logic is a form of algebra useful in drawing conclusions from insufficient, imprecise, or conflicting data sets and, presumably, mimics the way in which the brain arrives at conclusions. Fuzzy set theory was first proposed by the Azerbaijanian systems theorist/computer scientist Lofti A. Zadeh (1921- ) in 1965, and was used, initially, to demonstrate that many natural characteristics (such as height, baldness, beauty) contain indistinct and undiffer-entiated boundary lines. The notions of guppy effect and prototype theory indicate potential areas of weakness for fuzzy set theory. The guppy effect (described by the American psychologists D. N. Osherson and E. E. Smith in 1981) refers to an inconsistency or deviation in prototype theory in which a term is more prototypical of a conjunctive concept than of either, or any, of its constituent concepts (e.g., the term "guppy" - as well as the term "goldfish" - is assumed to be more prototypical of the conjunctive concept "pet fish" than of either of the separate constituent terms "pet" or "fish"). If prototype theory (i.e., a theoretical perspective concerning concepts and concept formation) is formulated within the parameters of fuzzy set theory, a potential contradiction occurs which implies that either fuzzy set theory or prototype theory is basically flawed. See also CONCEPT LEARNING/CONCEPT FORMATION, THEORIES OF; MIND/MENTAL SET, LAW OF; NEURAL NETWORK MODEL OF INFORMATION PROCESSING; PROTOTYPE THEORY; SET THEORY.

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