 The Diagnostic and Statistical Manual of Mental Disorders has been updated through the years and although no changes appear in the Glossary, some interesting shifts can be noted in the description of delusions which appear in the section on schizophrenia (compare DSM-IV, p. 275 and DSM-IV-TR p. 299 with DSM-5, p. 87). The new description seems to take into account some of the issues identified by Coltheart and others. For instance, in the DSM-5 delusions are described not as false, but as “fixed beliefs that are not amenable to change in light of conflicting evidence”. Leaving the details aside, some general comments apply to the style of the DSM definitions and descriptions of delusions. In so far as delusions are defined and described as irrational beliefs, it is difficult for them to be uniquely identified because their epistemic ‘faults’ are shared with other symptoms of psychiatric disorders, and with non-pathological beliefs. But definitions such as the ones in the DSM cannot probably be expected to provide necessary and sufficient conditions for the phenomena they aim to define. At best, they can prove diagnostically useful and guide further research by conveniently delimiting an area of investigation worth pursuing.