Today, we will take a look at all types of mental illnesses and see if we can put a structure over the apparently chaotic and unrelated/comorbid mental health conditions.
To start with, child and adolescent psychologists, at times, make a distinction between internalizing disorders and externalizing disorder.
Further factor analytical studies of both externalizing and internalizing disorders have revealed a factor structure of two underlying sub-factors in both domains.
Internalizing disorders, for example, have been consistently shown [pdf] to be made up of two factors—one labeled anxiety/fear and the other depression/distress. While phobias and panic disorder load heavily on fear/anxiety, depression (MDD), generalized anxiety disorder (GAD), post-traumatic stress disorder (PTSD) load heavily on distress/ depression. One easy way to remember the distinction is that while depression/distress is the "dislike" system—reacting to past or present real pain/trauma; fear/anxiety is the "distant" system—reacting to perceived danger/pain-in-future/dread of pain.
Similarly, externalizing disorders, have been shown to be made up of two sub-factors—one labeled (labels by me) mania/oppositional and the other anger/social norm violation. The first factor is characterized by hyperactivity, inattention, impulsivity, aggression, and perhaps alienation, while the second factor is characterized by disinhibition, rule-breaking, and anti-social, addictive, and violent tendencies. The mania/oppositional factor has disorders like ADHD and oppositional defiant disorder (ODD) loading on it, while conduct disorder (CD), adult antisocial behavior (AAB), drug use, etc., load heavily on the anger/social norm violation factor. Again, to make things easy to remember, mania/oppositional factor can be thought of as a "like" system—driven by what is pleasurable in the moment, while anger/social norm violation is a "want" system—driven by passionate desires and addictions without respect for social constraints.
So far is well-established science. Today I want to speculate a bit and propose two new classifications of psychopathologies—a relational disorder cluster as opposed to a reality distortion cluster.
The relational disorder cluster has, to boot, people problems. To be more specific, they have deficits in theory of mind (ToM) abilities. This again has a two sub-factor structure—where the inability in relating to people is more emotional in nature, but not cognitive, we have the factor of (lack of) sympathy functioning. When the deficit is more cognitive in nature, but one does not lack capacity to sympathize, the deficit is in that of (lack of) empathy. It is my contention that though autistic spectrum disorders (ASD) and psychopathy are related, as in both are mind-blind, the deficit in ASD loads on (lack of) empathy, while the deficit in psychopathy loads on (lack of) sympathy. While psychopaths perceive others as objects to be manipulated and used, an autistic considers the world as made up of only objects (including self) that need to be analyzed/investigated.
The reality distortion cluster is characterized by a willingness and ability to distort reality to suit one’s needs. This may entail loss of contact with objective, consensual reality. This again has a two sub-factor structure—the distortion of reality may limit itself to one’s self—or it may broaden to encapsulate the whole world of people and objects. While one factor is related to (lack of) insight about one’s own nature, the other factor is related to (lack of) insight about the world. It is my contention that though both dissociative disorders and psychotic spectrum disorders (PSD) are characterized by a loss of touch with reality, the former loads on (lack of) insight about self, while the latter loads on (lack of) insight about the world. While the depersonalization and de-realization experience of dissociation may be due to an emotional dissociation from one’s own self due to a past or present traumatic incident—leading to treating self as an object—the hallucinations and (paranoid) delusions of psychosis are mostly due to a cognitive dissociation from the world, due to an anticipated traumatic experience that is dreaded and avoided in this way, by turning away from the world.
So the final list of disorders looks like:
From the above, also note, that there is an opposition between mania and depression (good things are happening or bad things are happening); fear and anger (different and opposite (flight-fight reactions to looming threat); autism and psychosis (focus on things or focus on people), and thus I would say also between dissociation and psychopathy (using people or being used by others).
I would really love to see experiments done on the factor structure of relational and reality-distortion clusters to refute/support my hypothesis. In case such facts are already established, do let me know the relevant sources/pointers.