Delusion Although non-specific concepts of madness have been around for several thousand years, the psychiatrist and philosopher Karl Jaspers was the first to define the three main criteria for a belief to be considered delusional in his book General Psychopathology. These criteria are: certainty (held with absolute conviction) incorrigibility (not changeable by compelling counterargument or proof to the contrary) impossibility or falsity of content (implausible, bizarre or patently untrue) These criteria still live on in modern psychiatric diagnosis. In the most recent Diagnostic and Statistical Manual of Mental Disorders, a delusion is defined as: A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everybody else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person's culture or subculture