On the concept of delusions: Global trends and psychopathology in Japan.

The present article spotlights challenging conceptual and epistemological issues regarding delusions. A research history of various approaches to delusions in Europe, the United States, and Japan reveals the difficulty of defining delusions. Facing these difficulties, the standard concept of delusions has become thinner than the traditional ones, making its boundary with minority opinions vaguer. Nevertheless, clinical typology and epistemological approaches are contributing to the continuous conceptual refinement of delusions. Both standpoints validate and promote each other in elaborating the characteristics of delusions and their boundaries with non-delusions. In addition, epistemological inquiries into delusions shed new light on the extraordinarily difficult problems in the relationship among belief, knowledge, certainty, and delusions, contributing to epistemology in general. These approaches to delusions promote the evolution of the concept of delusions and related epistemological inquiries.