Professor Goldberg's suggestion ^{Reference Goldberg1} that our psychiatric classification should have a few major groupings of disorders that have common properties is very appealing and it is surely the direction in which psychiatry must aim to progress. This would help in the teaching of psychiatry, in reassuring those outside the discipline of its logical and scientific foundation and it would be of great benefit in clinical practice. However, although the specific categories he suggests have some clinical plausibility, they do not seem to be grounded in sufficient empirical evidence to justify their introduction. For example, a great deal of work is ongoing to understand the complex relationship between mood disturbance and psychosis. Much remains to be discovered but there is already substantial evidence for a complex overlap in the underlying pathogenesis of major mood and psychotic syndromes. ^{Reference Craddock and Owen2} Thus, it does not seem like a very good idea to draw what is likely to be an arbitrary distinction between ‘emotional disorders’ and ‘psychoses’. Similarly, if schizophrenia is shown to be a ‘neurodevelopmental disorder’, which category does it go in? It seems too early to set out broad categories, which may actually hamper progress over the coming years.

What about dimensions? At least for mood and psychotic disorders, we already know that there is a major overlap between underlying biology and we also know that dimensional approaches can provide useful clinical information over and above current diagnostic categories. ^{Reference Dikeos, Wickham, McDonald, Walshe, Sigmundsson and Bramon3} Hence, it is likely to be useful to encourage use of dimensional descriptions of psychopathology alongside the current categories.

The neuroscientific understanding of major psychiatric illness is advancing rapidly and can be expected to provide a rational basis for future psychiatric classifications that will have greatly increased clinical usefulness. ^{Reference Bullmore, Fletcher and Jones4} All changes come at substantial costs to the users of the classification – be they clinicians, patients, researchers, managers, administrators or politicians. Apart from the time and money expenditures required for training, there is the potential for confusion and for communication difficulty leading to problems in making comparisons across time. Thus, it is desirable that an appropriately high threshold is set when judging the advance in knowledge that is deemed necessary to justify each change. In this regard, it is important to be dispassionate and cautious in evaluating the strength and relevance of the increment in knowledge since previous classifications. We need to be fully aware of the problems and limitations with our current classification and start thinking in earnest about the future – but we are not there yet. Major changes should be justified by robust evidence and proven clinical utility.

While we await the evidence over the coming decade or two, we should be cautious in any changes that are made and realistic in our evaluation of the current evidence. ^{Reference Craddock5} Introducing descriptive dimensions alongside categories makes sense. Wholesale change of categories does not.