Irrationality and Pathology of Beliefs


Just as sadness is not always a symptom of mood disorder, irrational beliefs are not always symptoms of illness. Pathological irrational beliefs are distinguished from non-pathological ones by considering whether their existence is best explained by assuming some underlying dysfunctions. The features from which to infer the pathological nature of irrational beliefs are: un-understandability of their progression; uniqueness; coexistence with other psycho-physiological disturbances and/or concurrent decreased levels of functioning; bizarreness of content; preceding organic diseases known to be associated with irrational beliefs; treatment response to medical intervention, etc. Severe irrationality is sometimes caused by normal human motivation rather than by mental or physical dysfunction. Pure forms of self-deception may satisfy the diagnostic criteria of delusional disorder, but there may be no evidence that suggests that they are caused by illness. Although those with pathological delusions do not recognize their delusions as symptomatic of illness, differentiating pathological beliefs from normal irrational beliefs is vitally important: If a belief is pathological, psychiatrists must seriously consider treating the patient against her will. If it is not pathological, conversely, involuntary treatments are prohibited because they offend her basic autonomy.

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  1. 1.

    Several authors propose that delusions are not really a type of belief, but rather another type of mental state, such as imagination, illusion, or an intermediate mental state located between belief and non-belief ([24], to mention a few). The chief propositions of the present paper hold true even if delusions are best conceptualized as a mental state other than belief, because not all imaginations, illusions, and intermediate mental states are symptoms of illness. In this paper, without delving deeper into the recent debate between doxasticism and anti-doxasticism about delusions, I will assume that delusions are a kind of belief.

  2. 2.

    Many counterexamples have been raised against the idea that delusions are necessarily false in content. Those counterexamples include such cases as that of a wife who has a delusion of jealousy and whose husband actually is having an affair ([7], p. 106), and cases of the hypochondrical delusion that is expressed in a persistent claim of having gone “mad” ([8], p. 204). However, in these cases, the patients hold them based on wrong reasons. This observation suggests that the essential feature of delusion is epistemic irrationality rather than falsehood.

  3. 3.

    The standard terminology of psychiatry classifies false but persistent suspicions that do not reach conviction as “ideas” or “ideations,” and distinguishes them from delusions. For instance, whereas false and incorrigible convictions that “events, objects, or other persons in one’s immediate environment are seen as having a particular and unusual significance” are called “delusions of reference,” feelings or suspicions with the same content are termed “ideas of reference” ([6], p. 819, 823).

  4. 4.

    This is one of the differentiating features between delusional disorder and schizophrenia. In the former, “[a]part from the impact of the delusion(s) or its ramifications, functioning is not markedly impaired” ([6], p. 90), whereas in the latter, the “level of functioning in one or more major areas, such as work, interpersonal relations, or self-care, is markedly below the level achieved prior to the onset” (Ibid., p. 99), which is associated with volitional or cognitive impairment (Ibid., p. 100).

  5. 5.

    Miyazono rejected four positions, according to which delusions are pathological: (1) they are strange, (2) they are extremely irrational, (3) they are not explained by the folk psychological framework, and (4) responsibility-grounding capacities are impaired in those with delusions [20]. Among them, strangeness corresponds to bizarreness, and inexplicability by folk psychology roughly corresponds to the un-understandability I have already discussed. I agree with Miyazono in that those alternative proposals fail to explain what being pathological consists in. My contention is that the above-mentioned features are good indicators of an underlying dysfunction: Those features are not the criteria of being pathological, but the signs from which to infer the best explanation of the observed phenomena.

  6. 6.

    Murphy writes, “The mother appears to fit the DSM definition of delusion, yet many people I have asked about this case feel the pull of a different position (mothers, especially, feel this)” ([21], p.120). He holds back from definitely calling a case of self-deception a delusion because he restricts the term delusion for pathological cases.

  7. 7.

    Mele also pointed this out; see [43], p. 63.


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I have no funding to declare. I thank Kengo Miyazono, who read an early manuscript and provided detailed and enlightening comments. I wish to thank Hajime Honda, Hiroshi Ihara, Kazuya Kawase, Kohji Ishihara, Shigenori Tadokoro, Takeshi Kanasugi, Tetsuya Suzuki, Yudai Suzuki, Yukihiro Nobuhara, and Yutaka Morinaga for giving good feedback in workshops where I presented an early manuscript at the University of Tokyo and Kokugakuin University. I am also indebt to anonymous reviewers whose detailed comments were a great help to me.

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Sakakibara, E. Irrationality and Pathology of Beliefs. Neuroethics 9, 147–157 (2016).

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  • Delusion
  • Distinction between normality and pathology
  • Irrationality
  • Self-deception