On defining "mental disorder": purposes and conditions of adequacy.

All definitions of mental disorder are backed up by arguments that rely on general criteria (e.g., that a definition should be consistent with ordinary language). These desiderata are rarely explicitly stated, and there has been no systematic discussion of how different definitions should be assessed. To arrive at a well-founded list of desiderata, we need to know the purpose of a definition. I argue that this purpose must be practical; it should, for example, help us determine who is entitled to publicly funded health care. I then propose eight conditions of adequacy that can be used to assess competing definitions (e.g., the ordinary language condition, the coherence condition, and the condition of normative adequacy). These conditions pull in different directions, however, and we must decide which are most important. I also suggest that there is no single definition that can help us deal with all the relevant practical issues.