Delusions: the continuum versus category debate

Objective: In this paper I critically review the recently developed idea that delusions are best considered as part of a continuum along with more ordinary human beliefs. Method: A literature review of the area was guided by a Medline search, and supplemented with material already known to the author. Claims that recent research supports the continuum hypothesis is critiqued. Results: The argument and evidence advanced for the continuum approach to delusions depends largely on: (i) inadequacies of prevailing definitions of delusion, particularly in the light of evidence that delusional conviction is often not absolute; and (ii) the high prevalence of unusual beliefs in community populations. To the extent that the delusion construct contains much in addition to conviction and unusual or false belief content, the continuity approach is weak. The category of delusions continues to have some validity. Conclusion: Both categorical and continuous approaches to delusions have validity that depends at any time on our immediate clinical or scientific needs. No definitive resolution of the category versus continuum debate is likely to emerge.