On defining delusions

The DSM-III-R definition of delusions bears inconsistencies and does not account for the way delusions are detected clinically. It can be traced back to Karl Jaspers who was the first to mention the three criteria of delusions, which are to be found in the textbooks ever since: (1) certainty, (2) incorrigibility, and (3) impossibility or falsity of content. Psychiatrists always felt uncomfortable with the third criterion, and Kurt Schneider pursued the most thorough attempt to dispose of this criterion by his definition of delusional perception. It can be shown that while his definition is wrong, the phenomena he had in mind do, in fact, have some distinctive features. Proceeding from the first two criteria of Jaspers, a new definition is proposed that emphasizes the way certain contents are stated and disregards the issue of right or wrong. Advantages of this definition are discussed and a distinction between delusions (about external reality) and certain actual experiences (happening in the patient's mind) is proposed.