Schneider's definition of hallucinations and illusions

   In 1946, the German psychiatrist Kurt Schneider (1887-1967) defined hallucinations and illusions as follows: "For psychiatric diagnosis, among the many disorders of perception, the first among the experiential states, the most important ones are the sensory deceptions or misperceptions. It has been said time and again: these must involve sensory deception, i.e., that something sensory, experientially, not merely cognitive, is being experienced which is not there. That 'not there' is established objectively by the observer, not by the subject. When something is merely perceived as something else than it is in reality, we speak ofillusions."

   References

   Schneider, K. (1946). Klinische Psychopathologie. Stuttgart: Georg Thieme Verlag.