The most important idea for the reader is that the terms ‘diagnosis’, ‘medical model’ and ‘formulation’ all indicate conceptual approaches to labelling problems of mental or physical health. As abstract concepts, they have no physical reality, although physical or bodily changes may be part of the presentation. They are subject to change with time and fashion. Jaspers (1946) captured the risk from a tendency to reify concepts: ‘… error begins where instead of the idea there is an apparent accomplishment of the idea.’ Nevertheless, diagnostic approaches have a number of functions – in particular they provide a shorthand way of communicating about the health problems presented between doctors, and they should facilitate communication about needs for services of various kinds and about treatment and its likely outcome.