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Classification and external resources
ICD-10 F22.
ICD-9 297
MeSH D003702

A delusion is a fixed belief that is either false, fanciful, or derived from deception. In psychiatry, it is defined to be a belief that is pathological (the result of an illness or illness process) and is held despite evidence to the contrary. As a pathology, it is distinct from a belief based on false or incomplete information, dogma, stupidity, apperception, illusion, or other effects of perception.

Delusions typically occur in the context of neurological or mental illness, although they are not tied to any particular disease and have been found to occur in the context of many pathological states (both physical and mental). However, they are of particular diagnostic importance in psychotic disorders and particularly in schizophrenia, paraphrenia, manic episodes of bipolar disorder, and psychotic depression.


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 1917 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 continue in modern psychiatric diagnosis. The most recent Diagnostic and Statistical Manual of Mental Disorders defines a delusion 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.

There is controversy over this definition, as 'despite what almost everybody else believes' implies that a person who believes something most others do not is a candidate for delusional thought. Furthermore, it is ironic that, while the above three criteria are usually attributed to Jaspers, he himself described them as only 'vague' and merely 'external'.[1] He also wrote that, since the genuine or 'internal' 'criteria for delusion proper lie in the primary experience of delusion and in the change of the personality [and not in the above three loosely descriptive criteria], we can see that a delusion may be correct in content without ceasing to be a delusion, for instance - that there is a world-war.'.[2]

Furthermore, when a false belief involves a value judgment, it is only considered as a delusion if it is so extreme as to defy credibility. Since the delusional conviction occurs on a continuum, it can be inferred from an individual's behavior many times. A delusion and an overvalued idea tend to confuse. The latter implies that the individual has a unreasonable belief or idea but does not hold it as firmly as when a delusion takes place.[3]

Delusions are not due to a medical condition or substance abuse and they may seem believable at face value. Also, patients usually appear normal as long as another person does not touch upon their delusional themes.[4]

Delusions are not tied to any particular disease and they usually occur in the context of neurological or mental illness. Also, they have been found to occur in the context of many pathological states.[5]


Delusions are categorized into four different groups:

  • Bizarre delusion: A delusion that is very strange and completely implausible; an example of a bizarre delusion would be that aliens have removed the affected person's brain.
  • Non-bizarre delusion: A delusion that, though false, is at least possible, e.g., the affected person mistakenly believes they are under constant police surveillance.
  • Mood-congruent delusion: Any delusion with content consistent with either a depressive or manic state, e.g., a depressed person believes that news anchors on television highly disapprove them, or a person in a manic state might believe they are a powerful deity.
  • Mood-neutral delusion: A delusion that does not relate to the sufferer's emotional state; for example, a belief that an extra limb is growing out of the back of one's head is neutral to either depression or mania.[6]

In addition to these categories, delusions often manifest according to a consistent theme. Although delusions can have any theme, certain themes are more common. Some of the more common delusion themes are [6]:

  • Delusion of control: This is a false belief that another person, group of people, or external force controls one's thoughts, feelings, impulses, or behavior. A person may describe, for instance, the experience that aliens actually make them move in certain ways, and that the person affected has no control over these bodily movements. Thought broadcasting (the false belief that the affected person's thoughts are heard aloud), thought insertion, and thought withdrawal (the belief that an outside force, person, or group of people is removing or extracting a person's thoughts) are also examples of delusions of control.
  • Nihilistic delusion: A delusion whose theme centres on the nonexistence of self or parts of self, others, or the world. A person with this type of delusion may have the false belief that the world is ending.
  • Delusional jealousy (or delusion of infidelity): A person with this delusion falsely believes their spouse or lover is having an affair. This delusion stems from pathological jealousy, and the person often gathers "evidence" and confronts the spouse about the nonexistent affair.
  • Delusion of guilt or sin (or delusion of self-accusation): This is a false feeling of remorse or guilt of delusional intensity. A person may, for example, believe he has committed some horrible crime and should be punished severely. Another example is a person who is convinced he is responsible for some disaster (such as fire, flood, or earthquake) with which there can be no possible connection.
  • Delusion of mind being read: The false belief that other people can know one's thoughts. This is different from thought broadcasting, in that the person does not believe their thoughts are heard aloud.
  • Delusion of reference: The person falsely believes that insignificant remarks, events, or objects in one's environment have personal meaning or significance. For instance, a person may believe they are receiving special messages from newspaper headlines.
  • Erotomania is a delusion where someone believes another person is in love them. They believe this other person declared love first, often by special glances, signals, telepathy, or messages through the media.
  • Grandiose delusion: An individual is convinced they have special powers, talents, or abilities. Sometimes, the individual may actually believe they are a famous person or character (for example, a rock star). More commonly, a person with this delusion may believe they have accomplished some great achievement for which they have not received sufficient recognition (for example, the discovery of a new scientific theory). Often, this type of person believes they have uncovered an obvious "truth" that has escaped the entire history of humankind.
  • Persecutory delusion: These are the most common type of delusions and involve the theme of being followed, harassed, cheated, poisoned or drugged, conspired against, spied on, attacked, or obstructed in the pursuit of goals. Sometimes the delusion is isolated and fragmented (such as the false belief that co-workers are harassing), but sometimes are well-organized belief systems involving a complex set of delusions ("systematized delusions"). People with a set of persecutory delusions may believe, for example, they are being followed by government organizations because the "persecuted" person has been falsely identified as a spy. These systems of beliefs can be so broad and complex that they can explain everything that happens to the person.
  • Religious delusion: Any delusion with a religious or spiritual content. These may be combined with other delusions, such as grandiose delusions (the belief that the affected person is a god, or chosen to act as a god, for example).
  • Somatic delusion: A delusion whose content pertains to bodily functioning, bodily sensations, or physical appearance. Usually the false belief is that the body is somehow diseased, abnormal, or changed—for example, infested with parasites.
  • Delusions of parasitosis (DOP) or delusional parasitosis: The person believes that they are infested with an insect, bacteria, mite, spiders, lice, fleas, worms, or other organisms. They may also report being repeatedly bitten. In some cases, entomologists are asked to investigate cases of mysterious bites. Sometimes physical manifestations may occur including skin lesions.[7]


John Haslam illustrated this picture of a machine described by James Tilly Matthews called an "air loom," which Matthews believed was being used to torture him and others for political purposes.

The modern definition and Jaspers' original criteria have been criticised, as counter-examples can be shown for every defining feature.

Studies on psychiatric patients show that delusions vary in intensity and conviction over time, which suggests that certainty and incorrigibility are not necessary components of a delusional belief.[8]

Delusions do not necessarily have to be false or 'incorrect inferences about external reality'.[9] Some religious or spiritual beliefs by their nature may not be falsifiable, and hence cannot be described as false or incorrect, no matter whether the person holding these beliefs was diagnosed as delusional or not.[10]

In other situations the delusion may turn out to be true belief.[11] For example, delusional jealousy, where a person believes that their partner is being unfaithful (and may even follow them into the bathroom believing them to be seeing their lover even during the briefest of partings) may result in the faithful partner being driven to infidelity by the constant and unreasonable strain put on them by their delusional spouse. In this case the delusion does not cease to be a delusion because the content later turns out to be true.

In other cases, the delusion may be assumed to be false by a doctor or psychiatrist assessing the belief, because it seems to be unlikely, bizarre or held with excessive conviction. Psychiatrists rarely have the time or resources to check the validity of a person’s claims leading to some true beliefs to be erroneously classified as delusional.[12] This is known as the Martha Mitchell effect, after the wife of the attorney general who alleged that illegal activity was taking place in the White House. At the time her claims were thought to be signs of mental illness, and only after the Watergate scandal broke was she proved right (and hence sane).

Similar factors have led to criticisms of Jaspers' definition of true delusions as being ultimately 'un-understandable'. Critics (such as R. D. Laing) have argued that this leads to the diagnosis of delusions being based on the subjective understanding of a particular psychiatrist, who may not have access to all the information that might make a belief otherwise interpretable. R.D. Laing's hypothesis has been applied to some forms of projective therapy to "fix" a delusional system so that it cannot be altered by the patient. Psychiatric researchers at Yale University, Ohio State University and the Community Mental Health Center of Middle Georgia have used novels and motion picture films as the focus. Texts, plots and cinematography are discussed and the delusions approached tangentially.[13]. This use of fiction to decrease the malleability of a delusion was employed in a joint project by science-fiction author Philip Jose Farmer and Yale psychiatrist A. James Giannini. They wrote the novel Red Orc's Rage, which, recursively, deals with delusional adolescents who are treated with a form of projective therapy. In this novel's fictional setting other novels written by Farmer are discussed and the characters are symbolically integrated into the delusions of fictional patients.This particular novel was then applied to real-life clinical settings.[14]

Another difficulty with the diagnosis of delusions is that almost all of these features can be found in "normal" beliefs. Many religious beliefs hold exactly the same features, yet are not universally considered delusional. These factors have led the psychiatrist Anthony David to note that "there is no acceptable (rather than accepted) definition of a delusion."[15] In practice psychiatrists tend to diagnose a belief as delusional if it is either patently bizarre, causing significant distress, or excessively pre-occupies the patient, especially if the person is subsequently unswayed in belief by counter-evidence or reasonable arguments.

It is important to distinguish true delusions from other symptoms such as anxiety, fear, or paranoia. To diagnose delusions a mental state examination may be used. This test includes appearance, mood, affect, behavior, rate and continuity of speech,evidence of hallucinations or abnormal beliefs, thought content, orientation to time, place and person, attention and concentration, inside and judgment, as well as short-term memory.[16]

Johnson-Laird suggests that delusions may be viewed as the natural consequence of failure to distinguish conceptual relevance. That is, the person takes irrelevant information and puts it in the form of disconnected experiences, then it is taken to be relevant in a manner that suggests false causal connections. Furthermore, the person takes the relevant information, in the form of counterexamples, and ignores it.[17]

Development of specific delusions

The top two 'Factors mainly concerned in the germination of delusions' are:1. Disorder of brain functioning and 2. background influences of temperament and personality.[18]

Higher levels of dopamine qualify as a symptom of 'disorders of brain function'. That they are needed to sustain certain delusions was examined by a preliminary study on delusional disorder (a psychotic syndrome), instigated to clarify if schizophrenia had a dopamine psychosis.[19] There were positive results - delusions of jealousy and persecution had different levels of dopamine metabolite HVA (which may have been genetic). These can be only regarded as tentative results; the study called for future research with a larger population.

It is too simplistic to say that a certain measure of dopamine will bring about a specific delusion. Studies show age[20][21] and gender to be influential and it is most likely that HVA levels change during the life course of some syndromes.[22]

On the influence personality, it has been said: "Jaspers considered there is a subtle change in personality due to the illness itself; and this creates the condition for the development of the delusional atmosphere in which the delusional intuition arises."[23]

Cultural factors have "a decisive influence in shaping delusions".[24] For example, delusions of guilt and punishment are frequent in a Western, Christian country like Austria, but not in Pakistan - where it is more likely persecution. It says cultural factors have a decisive influence in shaping delusions.[25] In a series of case studies, delusions of guilt and punishment were shown in Austria as well and this is with Parkinson's patients treated with l-dopa - a dopamine agonist.[26]


To define delusional thinking in a specific patient, it is important to consult a local psychiatrist who can make a thorough examination before diagnosing the problem.[27] Explaining the causes of delusions has been challenging and several theories have been developed. One is the genetic or biological theory, which states that close relatives of people with delusional disorder are at increased risk of delusional traits. Another theory is the dysfunctional cognitive processing, which states that delusions may arise from distorted ways people have of explaining life to themselves. A third theory is called motivated or defensive delusions. This one states that some of those persons who are predisposed might suffer the onset of delusional disorder in those moments when coping with life and maintaining high self-esteem becomes a significant challenge. In this case, the person views others as the cause of their personal difficulties in order to preserve a positive self-view.[28]

This condition is more common among people who have poor hearing or sight. Also, ongoing stressors have been associated with a higher possibility of developing delusions. Examples of such stressors are immigration or low socio-economic status.[29]

Researcher, Orrin Devinsky, MD, from the NYU Langone Medical Center, performed a study that revealed a consistent pattern of injury to the frontal lobe and right hemisphere of the human brain in patients with certain delusions and brain disorders. Devinsky explains that the cognitive deficits caused by those injuries to the right hemisphere, results in the over compensation by the left hemisphere of the brain for the injury, which casues delusions.[30]

A study carried out by a team from The Warwick Medical School at the University of Warwick, Coventry, England, leaded by Andrea Schreier, Ph. D., indicated that children who suffered bullying are more likely to develop psychotic symptoms in early adolescence. The background facts demonstrated that hallucinations and delusions are common in childhood as well as in adulthood and that children who experience such symptoms are more prone to develop psychosis later in life. Furthermore, the study demonstrated that the risk of psychotic symptoms, including delusions, was multiplied by two for children who suffered bullying at age eight or ten. The authors remark that bullying can cause chronic stress that may have an effect on a genetic predisposition to schizophrenia and result in setting off the symptoms.[31]

See also

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Further reading

  • Bell V, Halligan PW, Ellis H (2003). "Beliefs about delusions" (PDF). The Psychologist. 16 (8): 418–423. 
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  • Coltheart M., Davies M., ed. (2000). Pathologies of belief. Oxford: Blackwell. ISBN 0-631-22136-0. 
  • Persaud, R. (2003). From the Edge of the Couch: Bizarre Psychiatric Cases and What They Teach Us About Ourselves. Bantam. ISBN 0-553-81346-3. 

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  2. Jaspers 1997, p. 106
  3. "Terms in the Field of Psychiatry and Neurology". Retrieved 2010-08-06. 
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  9. Spitzer M (1990). "On defining delusions". Compr Psychiatry. 31 (5): 377–97. doi:10.1016/0010-440X(90)90023-L. PMID 2225797. 
  10. Young, A.W. (2000). "Wondrous strange: The neuropsychology of abnormal beliefs". In Coltheart M., Davis M. Pathologies of belief. Oxford: Blackwell. pp. 47–74. ISBN 0-631-22136-0. 
  11. Jones E (1999). "The phenomenology of abnormal belief". Philosophy, Psychiatry and Psychology. 6: 1–16. 
  12. Maher B.A. (1988). "Anomalous experience and delusional thinking: The logic of explanations". In Oltmanns T., Maher B. Delusional Beliefs. New York: Wiley Interscience. ISBN 0-471-83635-4. 
  13. Giannini AJ (2001). "Use of fiction in therapy". Psychiatric Times. 18 (7): 56. 
  14. AJ Giannini. Afterword. (in) PJ Farmer. Red Orc's Rage.NY, Tor Books, 1991, pp.279-282.
  15. David AS (1999). "On the impossibility of defining delusions". Philosophy, Psychiatry and Psychology. 6 (1): 17–20. 
  16. "Diagnostic Test List for Delusions". Retrieved 2010-08-06. 
  17. "A New Definition of Delusional Ideation in Terms of Model Restriction". Retrieved 2010-08-06. 
  18. Sims, Andrew (2002). Symptoms in the mind: an introduction to descriptive psychopathology. Philadelphia: W. B. Saunders. p. 127. ISBN 0-7020-2627-1. 
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  20. Mazure CM, Bowers MB (1 February 1998). "Pretreatment plasma HVA predicts neuroleptic response in manic psychosis". Journal of Affective Disorders. 48 (1): 83–6. doi:10.1016/S0165-0327(97)00159-6. PMID 9495606. 
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  22. Tamplin A, Goodyer IM, Herbert J (1 February 1998). "Family functioning and parent general health in families of adolescents with major depressive disorder". Journal of Affective Disorders. 48 (1): 1–13. doi:10.1016/S0165-0327(97)00105-5. PMID 9495597. 
  23. Sims, Andrew (2002). Symptoms in the mind: an introduction to descriptive psychopathology. Philadelphia: W. B. Saunders. p. 128. ISBN 0-7020-2627-1. 
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  25. Stompe T, Friedman A, Ortwein G; et al. (1999). "Comparison of delusions among schizophrenics in Austria and in Pakistan". Psychopathology. 32 (5): 225–34. doi:10.1159/000029094. PMID 10494061. 
  26. Birkmayer W, Danielczyk W, Neumayer E, Riederer P (1972). "The balance of biogenic amines as condition for normal behaviour" (PDF). J. Neural Transm. 33 (2): 163–78. doi:10.1007/BF01260902. PMID 4643007. 
  27. "Delusional Disorder Definition". Retrieved 2010-08-06. 
  28. "Delusional Disorder". Retrieved 2010-08-06. 
  29. "Causes of Delusional Disorder". Retrieved 2010-08-06. 
  30. "What causes delusions?". Retrieved 2010-08-06. 
  31. "Children Who Suffered Bullying Are More Likely To Develop Psychotic Symptoms In Early Adolescence". Retrieved 2010-08-06.