How can novelists have real multiple personality—not just something that superficially resembles multiple personality—yet not be mentally ill? Here is how.

Let me make an analogy about two groups of people who have heard strange music in their head since they were children. To put it bluntly, everyone in both of these groups hallucinates (music). However, the people in Group A, through no fault of their own, have always been dysfunctional, because their music hallucinations have always distracted them, and kept them from accomplishing much in life. Whereas, the people in Group B, inspired by their musical hallucinations, have become composers, some quite good. In short, both groups really do have hallucinations, but the people in Group A have an illness, while the people in Group B do not.

Multiple personality disorder (the mental illness) comes in a very wide range of function and can be misdiagnosed as almost anything. Some are so dysfunctional that they are misdiagnosed as having schizophrenia. Others appear to have bipolar disorder, because one personality is depressed and pessimistic, while another personality is outgoing and optimistic. And there are many other people with multiple personality disorder who do have a genuine mood disorder, such as depression, which affects most of their personalities, but only the depression gets diagnosed.

Clinically, the most practical way to screen for multiple personality is to ask the person if they ever have memory gaps or lose time, since one personality may have amnesia for the period of time that another personality has been out and in control. Neither schizophrenia nor bipolar disorder nor depression nor any other psychiatric condition—only multiple personality—has a history of sober memory gaps (if someone claims alcoholic blackouts, which may be due to a personality who drinks, ask if they have ever had a “dry” blackout, even a relatively short one, since another alternate personality may not drink).

But multiple personality disorder—which is a “disorder,” because it causes distress and/or dysfunction—represents only a small fraction of the people who have multiple personality, as shown by all the novelists who have multiple personality (see this blog), but who are not mentally ill.