Is Multiple Personality a Disorder?
Disability: (re: United States Rehabilitation act of 1973) A "physical or mental impairment which substantially limits one or more major life activities."
Multiple personality, as viewed by psychology, is one end of a spectrum of dissociation. Dissociation is normal. And if one reads the section on everyday multiplicity, even multiple personality is relatively normal.
Think about families. A family is a group dynamic. In groups, sometimes small problems become magnified -- the interactions between people who have known each other for a long time sometimes develop patterns and habits that are difficult to break, and sometimes less-than-functional.
Multiples are an "internalized family" of sorts (see also The Multiple System) and as such a person with multiple personality can suffer internally from all sorts of issues that many families face, along with some additional complications that come from sharing a body and having to divvy up time between several people to actually interact with the world.
Just as some families are more functional than others, some multiples are more functional1 than others.
This site does not refer to all multiples as automatically dysfunctional or disordered. However, like many family systems, even the functional ones, a multiple system could probably benefit from some good advice and help from time-to-time, hence a resource such as this one, where multiples who are healthy and who are not can get some advice on how to better deal with times of trouble and with the inevitable rough spots that happen from time to time.
It makes more sense to treat multiple personality as one of many different expressions of the "Self" in this world, and to add to the diversity of the human experience than it does to lump everyone who is multiple under a broad sweeping heading of dysfunctional.
So why is it that multiple personality (disorder) is now called dissociative identity disorder?
There's several stories behind this, but mainly let's keep it to the simple fact that it was changed in the 1990s in the DSM2. There's some tweaks to the criteria for the disorder, but it still covers the main bases.
Where "multiple" is easily derived from "multiple personality disorder", it's not as easy to derive a descriptor or identity marker from DID. Unfortunately "multiple personality" is more readily recognized throughout our culture, and although there has been a somewhat recent shift in awareness in the general population, it's usually driven by media stereotyping and the perpetuation of harmful bias, oppression and misinformation about what it is really like, and what the dangers New really are.
1 Note there's a lot of controversy about the term "functional" as it usually is heavily laden with capitalist society expectations of being able to work. Here, it is meant as being able to do the things you want and need to do to attain a contented existence with attainable challenges, and thus is entirely subjective. ⇑
2 Diagnostics & Statistics Manual, which is used to catalog known/current diagnostic criteria for psychologists and psychiatrists. ⇑