Explaining Multiplicity vs Plurality as used on this site
Introduction - in short
Multiplicity: The Missing Manual (this section of the kinhost.org website - pages in the "Main" group on the website if you look at the webpage address) is for folk who struggle with plurality in some way, many of whom qualify for a mental health diagnosis. There are many ways to be plural without qualifying for a mental health diagnosis.
What is "Plurality"?
Plurality, loosely defined, is the experience of being many (in one body).
People experiencing plurality are "plurals" (lowercase). This is a loose descriptive term, not an identity label.
Many "what"? Various plurals self-describe what they experience as parts, people, alters, spirits, voices, entities, others, insiders, fragments, tulpas, fictives/factives, mosaics, selves, duplicates, copies, past lives, etc.
The most generic and non-controversial inclusive blanket terms for the subjective "many" being experienced are: headmates, system members, insiders or others. These terms (and others) are used throughout this manual, interchangeably. These generic terms may change over time, or may change in context of the writing or authors on the site, so other terms may be discovered depending who wrote it, and when it was written (this is a wiki website with many authors and contributors).
Who are Plurals with a capital "P"?
A portion of the people experiencing plurality may also use the identity label "Plural" to self-describe. All group entities fit under the loose broad umbrella of plurality and thus are plural without the capital letter indicating Plural Pride New or Plural activism New. These people are often using it as a generic descriptor rather than an identity label (or have not adopted the capitalization convention yet).
The community is relatively new, as communities go, and while there is a convention to capitalize or lowercase plural, borrowed from the Deaf community (as in Deaf Pride), it is not a widely used convention in the plural community at large (yet?).
So plurals are anyone who experiences being many (something) — the overall umbrella — and Plurals are the proud members of the Plural Movement New, exhibit or promote Plural Pride New and have decided to explicitly adopt the term "plural" as an identity label rather than a blanket descriptor.
What are "Multiples"?
The term "multiple" originated from the diagnosis "Multiple Personality Disorder" and it's difficult to tell whether it was coined by the professionals who viewed (per the DSM criteria at the time) all plurals as in need of treatment, or if it was coined by the people being treated. Regardless, the term "multiple" is one of the grandfathered in identities in the wider-umbrella plural community that mainly depicts those plurals who have or could qualify for a medical diagnosis. It's a loose term, and can apply to those who self-diagnose, those who have been in the mental health system for a significant amount of time, and/or those who believe in the medical model or not.
The term "multiple" is falling out of use because it's a medical model term based on an old abandoned diagnostic label. However, it's still used by a very significant number of folk in the community.
Multiple/Plural/DID Systems - or just "Systems"
The term "system" to describe multiples or plurals comes from Systems Theory as used by Morton Prince, and many other medical-model/psychology authors occasionally using the term both in writing and in the therapeutic environment. This has filtered into the plural community as a potential (and currently popular) replacement for "multiple" to selves-describe the complicated inter- and inner-relationships between headmates or others in their body.
Everything is a system, according to Systems Theory. Even singular people are still systems. The Crisses explains this issue in a video. Thus it's actually necessary to have clarification or context to use the term "system" unless one is referring to a method of doing something or a process — and sometimes when one is making a vague references to a larger enveloping system ("I'm trying to get things done, but I'm always blocked by The System." referring to the complex machinery of society, culture, government, laws, resources, etc. that envelops oneself and what one is attempting to do.)
Hence when people are referring to "systems" in the community, they are leaving out the descriptor preceding it "We are a system." makes little sense unless there's an omitted term like "We are a [multiple] system." or "We are a [DID] system." We try to clarify "system" on this website as much as possible to avoid confusion about when we are talking about "the system" like one would talk about "the man" or "society" versus when we're talking about the complex subjective, relational, and mental mechanics inside of a plural entity. We attempt to avoid using "system" or "systems" as a generic identity or community identifier. The term as used on this site is process-oriented, and all plural entities work under the same rules and laws of Systems Theory as all other entities do, so it can be very helpful to consider portions of plural experiences from a systems (as in Systems Theory) perspective.
Singularity-Plurality is a Spectrum
Plurality is a normal aspect of human experience. Many singular folk when approached by a plural will say they have moods, or modes, or aspects, or roles, personality cubbies, etc. Certainly! When viewing all of humanity, there's no sudden high-contrast difference between singularity and plurality. It's a greyscale. Many singular folk have moments of more-or-less plural experiences, but there are definite ends of the spectrum and when one takes points along the spectrum and compare them, there are some very drastic differences that can be a game-changer for how one lives life and experiences strengths and adversity.
So the opposite experiences to plurality are singularity. And there are many folk who are quite absolutely plural (with identity shifts so profound they are most definitely a lot of people sharing a body), so thus there are also folk who are quite absolutely singular (with little to no shift in identity or perspective between very different scenarios). The degree to which any particular human body's experiences are primarily plural or primarily singular can affect many aspects of their life.
Most people won't be comfortable with any terms for singular folk — in the past they've been called "singlet" or "singleton" and the community is moving away from those terms and simply using "singular" but there's still some resistance in the vein of "We are just normal. You are the weird ones who need a label and need to get fixed." This happens to all oppressed communities when they find a voice and start to organize.
The overall culture around us is singular-centric. The majority of the time: singularity is assumed, people are treated as one-entity-per-body, singularity is reinforced, plurality is shamed or there is peer-pressure and bullying to hide plurality, and denial that plurality even exists. Note that all of these support and continue the myth that plurality is rare or that it's fake. More about that in the Movement section of kinhost.org New.
On this site we will use least controversial terms singular folk, singularity, singular-centrism, etc. without hiding the fact that singular-centrism and singular people do exist and affect plurals and multiples.