[What is a delusion? A phenomenological view]

The debate about dimensional or categorised classification ofsymptoms has widened to include the concept of delusions, one of the key notions in psychiatry. Although interrater agreement concerning the delusion concept is considerable, it is extremely doubtful whether approval also extends to the construct validity. Can the delusion concepts till be described according to the DSM-criteria?

To describe the history of the delusion concept and to present current views on the subject.

The literature was reviewed with the help ofPubMed.

A delusion can best be described as an individual and personal view which cannot befalsifted and to which patientsfeel emotionally attached. Most people consider a delusion to be implausible because it is expressed with such unshakeable certainty. With regard to a a dimension such as conviction there seems to be a continuum that extends from normal ideas to impaired reality-testing.

If delusions are to be considered as dimensional constructs this will give rise to questions concerning discriminant validity. It will become increasingly difficult to discriminate between delusions and other types of belief that are associated with impaired reality-testing.