Here’s a hypothesis: there are two broad types of mental disorder, and distinguishing between them might aid in understanding their causes as well as in diagnosis and treatment. The idea springs from my thoughts on the evolutionary forces that have shaped our psychology, particularly in selecting for a diversity of personality types and cognitive styles.
First up, I define mental disorder along pretty broad functional lines as being any lasting psychological condition that hampers an individual’s ability to pursue their interests. I prefer the functional approach (as I do in many cases) rather than trying to dig around to find some essential core or set of features that characterises all mental disorders, but that doesn’t preclude other modes of defining mental disorder.
The benefit of the functional approach is in seeing the mind as an evolved tool, the function of which is to produce behaviours that serve to satisfy our interests (defining what these interests are is another important issue, but I’ll leave that to one side for now).
So, in this light, I propose that there are two broad types of mental disorder: