Plural

A Plural, or a Multiple, is a person or collection of persons who experiences, one way or another, life as several people instead of one. Tulpamancy is an example of one form, usually described as a dedicated effort to create a sentient friend or companion. Another is those with the clinical diagnosis of Dissociative Identity Disorder. Among other things, persons with this diagnosis must experience other personalities, termed alters, who can front and take over the body. When another person is in front, the original, if there is one, loses consciousness and has no memory of what happened. These two very different manifestations of plurality are by no means the only forms of plurality.

In addition, plurality exists on a spectrum. The term median has been created to cover those individuals who feel there is more than one person in the body, but they are not entirely separate from each other. Even with this term, it only covers one way in which a person can lie between being a singlet and a plural.

History
Manifestations of plurality have likely existed for centuries before thorough records were kept. It has only been recently, with the advent of the internet, and more scientific mindsets, that this relatively rare phenomenon has become documented.

In the past, it is likely that individuals who demonstrated plurality would have had their condition interpreted in ways that fit the local culture. Ideas of spirit possession, spirit channelling, familiars, doppelgangers, religious visions, and muses, may have all been caused by plurality, or plurality may have been included in them.

In the more recent past, around the middle of the twentieth century, riding on the wave of scientific excitement that has been building since the enlightenment, this phenomenon was pathologised in several forms, alongside many other things, and included in psychological canon. These forms include the various dissociative disorders, and also, possibly, schizophrenia. Recent efforts have been attempting to clean up the diagnostic standards, resulting in some effort to separate plurality out from the disorders it is associated with.

The history of tulpamancy itself extends back to a single book by a french adventurer, Alexandra David-Neel, titled "Magic and Mystery in Tibet". This book contains a short depiction of the process of creating a Tulpa. It combines elements of Theosophy, a western religion, and arcane Buddhism, a religion of Tibet, two belief systems that have some connection to the ideas of plurality.

(primary reference) Tracking the Tulpa

Plurality in fiction writers
A form of plurality has been discovered among those who write fiction for a living. It has been found that the characters of such authors with high frequency talk back to the author, and even assist them in writing their books. Some authors even need to negotiate with the characters, asking them to do one thing or the other, and being told, "no". This phenomenon, particularly in more extreme cases, has been termed the Illusion of Independent Agency.

(primary reference) IIA paper