Beliefs that clearly oppose reality, often focused on themes of persecution or an exaggerated sense of self-importance, qualify as delusions.
Delusions are usually experienced by people who have a severe psychotic disorder, often schizophrenia or bipolar illness. Delusional thinking can occur in other types of individuals, for example, as the result of drug or alcohol abuse. Delusional ideas fall into a number of categories. A common type is delusions of grandeur, in which individuals imagine they have some God-given purpose. Some people actually believe they are historical personalities of great importance, such as Jesus or Joan of Arc. The inverse of these delusions of grandeur are the delusions of persecution. During such delusions individuals believe that some person or group is out to harm them. Still another set of delusions are referred to as command hallucinations. During command hallucinations individuals hear voices telling them to commit an act. These delusional thoughts often lead people to acts of self-mutilation, starvation, or suicide or to violent criminal acts. Rarer yet are encapsulated delusions, delusions that are restricted to one specific belief or part of these individuals' life. These delusions may not directly affect the individuals' functioning. For example, individuals might believe that a movie star is speaking to them directly and may find the belief pleasant. The romantic delusion does not cause these persons distress or make them unable to reality-test other beliefs.
Many psychological disorders feature aspects of delusional thought. People with depression often experience the delusion that they are worthless, sinful, or too unlikable to belong to any group. Other forms of delusional thinking occur in people with somatoform and dissociative identity disorders. These include body dysmorphic disorder, obsessive-compulsive disorder, and multiple personality disorder.
John Junginger, a clinical scientist at Indiana University, studied 138 individuals who exhibited delusional beliefs and developed a scale of bizarreness. Junginger identified the 12 types of delusional beliefs (including those mentioned above) as well as several others, such as insertion and control. After categorizing delusional thoughts as such, Junginger conducted another study, attempting to discern how well his categories could predict violent behavior. Describing the study in Omni magazine, Steve Nadis wrote that “Junginger suspects psychotics are more likely to act out their false beliefs if they have involved, highly ‘systematized’ delusions.” Elaborate delusional beliefs correlate more highly with violent behavior than vague delusional beliefs. Individuals who believe that an unidentified person is out to hurt them is less likely to act violently than someone who believes that a specific neighbor has been sending him messages through the walls to kill himself. Psychologists once believed that people with delusions were unable to question them or have perspective on their unreality. Subsequent research suggested that young people developing schizophrenia are actually scared by their delusions and experience them, during onset of the disease, as dystonic, that is, characteristic of a some kind of disease.
Bortolotti, Lisa. Delusions and Other Irrational Beliefs. Oxford: Oxford University Press, 2010.
Chadwick, Peter K. Borderline: A Psychological Study of Paranoia and Delusional Thinking. London: Routledge, 2014.
Nadis, Steve. “Dangerous Delusions: Making Sense of Senseless Behavior.” Omni (December 1994): 32.
Starr, Cynthia. “A ‘Secret Disorder’ Yields to Serotonin Reuptake Inhibitors.” Drug Topics (5 July 1993): 20.