Fuzzy Logic in the Psychology of Concepts George J. Klir Binghamton University (SUNY-Binghamton) Binghamton, NY 13902 [email protected] Abstract It is well known that the emergence of fuzzy set theory and fuzzy logic in the 1960s was motivated primarily by the perceived need for mathematics capable of representing and dealing with common-sense concepts used by humans and expressed in natural language. It is thus very peculiar that fuzzy logic has been completely rejected in the psychology of concepts — a research area that is specifically oriented to studying concepts of this kind. After introducing the meaning of the term “concept” in the psychology of concepts and the main psychological theories of concepts, I will address the principal issue of my lecture: Why has fuzzy logic been rejected in the psychology of concepts? I will show that the rejection was a result of arguments presented in a single paper published in 1981 by two highly influential psychologists, Osherson and Smith. Even though it is now well known that all arguments in this paper are fallacies of several different types, as I will demonstrate in some detail, the paper has enormously influenced the whole field of the psychology of concepts, and has delayed a fruitful cooperation between psychologists of concepts and mathematicians specializing on fuzzy logic for some three decades. This is reminiscent of the well-documented story in the field of artificial neural networks, where research was severely inhibited for many years by publication of the very influential book Perceptrons by Minsky and Papert in 1969. What can be done to ameliorate this very unfortunate situation? After presenting an overview of what has already been done in this regard, I will argue that circumstances are now becoming favorable for cooperative research between psychologists of concepts and researchers in the fuzzy logic community and that such cooperation is likely to highly beneficial for both areas. I will conclude the lecture by identifying some challenges for fuzzy logic from the psychology of concepts as well as some challenges for the psychology of concepts from fuzzy logic.