Writers’ belief that their characters, narrators, and muses have minds of their own is based on regular personality’s amnesia for the others’ thinking process.

There are two essential criteria for multiple personality: 1. more than one psychological entity with a sense of its own personhood, and 2. amnesia of at least one personality for one other (many personalities may be partially co-conscious with each other).

However, the second criterion is really entailed in the first criterion, because amnesia is what gives one personality a sense of its own personhood. The main basis for two personalities to believe that they are separate persons is that they don’t have the same memories.

Why do writers’ regular personalities believe that their characters, narrators, and muses have minds of their own? Their belief is based on their characters,’ narrators,’ and muses’ having opinions and information that are based on thoughts for which the regular personality has amnesia. The regular personality does not remember the narrator’s or muse’s thought process in thinking up the story, or the thinking by which a character formed its opinions.

As to dramatic, overt examples of one of a writer’s personalities having amnesia for another, I could cite instances of writers’ having fugues. (Search “fugue.”) Also, I have quoted some writers as saying that when they read their past works, they may not remember having written them.

But do writers have “real” multiple personality if they are not overtly flipping from one personality to another? Overt, easily recognizable switching is a feature of 1. multiple personality that is being presented, post-diagnosis, as a public demonstration, or 2. a case that is out of control.

Most of the time, in real multiple personality, alternate personalities remain inside (sometimes heard as voices), or come out incognito. And in writers, alternate personalities are more or less under contract to limit their overt appearances to the writing study.