Plural people are people who have more than one person per brain. Your brain is naturally designed to create an identity, that’s how you were made. Under certain circumstances, it can do that more than once. Leonard Nimoy, the actor who played Spock, has described having conversations in his head with Spock, who seemed to have a mind of his own.
The most well known plural system in history or fiction would be Bruce Banner and the Hulk. In the canon of marvel comics, Bruce was beaten by his father as a small child and he shoved all his anger into a separate part of his brain, which developed into the personality of the Hulk. The gamma radiation accident didn’t create the Hulk, it just gave the Hulk a different body than Bruce’s. Bruce has dissociative identity disorder, which is a real psychiatric disorder that works exactly as I’ve just described. Moon Knight also has it.
Plurality is not an illness or a disorder. Plurality can arise as a result of psychiatric distress, but it can also arise due to religious, spiritual, cultural, or psychedelic experiences, and the latter category will not be documented in the DSM or similar texts because it’s not an illness. As for disordered plurality, examples include DID and OSDD.
You will note the DSM criteria for DID state:
The disturbance is not a normal part of a broadly accepted cultural or religious practice. Note: In children, the symptoms are not better explained by imaginary playmates or other fantasy play.
For example, some buddhist monks practiced the ritual of creating a foreign being within their mind, called a tulpa. Some people exploring plurality in the modern day have noted that the spiritual practices performed by these buddhists are remarkably similar to prayer, and that perhaps christians who claim to be able to “talk to god” are in fact talking to a tulpa they created themselves.
Some people with narcissistic personality disorder have reported plural-like experiences, due to the exceedingly flexible egos of many pwNPD. Actors and roleplayers have as well, due to the nature of their hobbies in creating the outward appearance of a second identity, which can sometimes be mirrored on the inside. Some plural people just are, with little discernable cause. It appears to be entirely natural in these cases, and there’s no reason that can’t be the case, because the mechanism of the brain that creates identity is natural too, and sometimes it just doesn’t work normally.
In the case of plural disorders like DID and OSDD, the plurality is not the illness. The illness is the disordered nature of the plurality. DID’s characteristic symptoms are switch amnesia and dissociative barriers. Members of the system, or alters, cannot talk to one another and plan with these barriers in place. Much of therapy focuses on breaking down these mental walls and learning to coexist as multiple people in the same body. Once this is achieved, the system is no longer disordered, but they are still plural.
