The Multiple

Pluarlity/Multiplicity is the state of having multiple entities inhabiting a single physical body. The plural experience is extremely diverse, and this carrd aims to help start you out with understanding it.You may contact us, Ozymandias, at !! PUNZOP ¡¡#0666 for questions, comments and conerns.

Terminology


Here's a collection of common words you'll find in plural spaces!System/Collective
The collection of people and entities, often called headmates, that share a single physical plural body
Alter/Sysmate/Headmate/etc
A singular person or entity in a plural system or collective. Some systems are more comfortable with one term over the other, and it's polite to ask which term is preferred. In this Carrd they will be referred to as "headmates" though.
Dissociation
a mental process of disconnecting from one's thoughts, feelings, memories or sense of identity. Those who dissociate may feel disconnected from reality, confused, lethargic, numb, and have a slow or altered sense of time.
Dissociative Amnesia
Dissociative amnesia is, more or less, exactly what the name suggests. it's amnesia, or loss of time, associated with or caused by dissociation. Usually the amount of amnesia a system has varies from system to system.
Disordered Plurality
Plurality that is affected or caused by a disorder of some kind, or causes significant distress and disturbance in a plural's life. The most common disorders to affect plurality are (P-)DID and OSDD, but the disorder that affects a plural's identity can be any of them. Such as BPD, MaDD, DP/DR, Schizophrenia, and more. A disordered plural can be any origin.
Non-disordered Plurality
Plurality that is NOT affected or caused by a disorder. This doesn't mean that the plural in question doesn't have any disorder at all, it just means their system was not caused or hindered by it. A non-disordered plural can be any origin, though are commonly seen using labels under the non-traumagenic umbrella. Non-disordered plurals CAN be trauamgenic, though, as trauma in and of itself is not a disorder.
Front/Fronting
Fronting is an activity performed by one or more headmates, where they take control of the body and handle daily activities and communication. Often, systems have a fronting room/area they go to when they front. A fronting room is a dedicated area in headspace that members of the system visit in order to front.
Frontstuck
Exactly what it sounds like. When a headmate is stuck in front. Often times it's a single headmate, but there can be multiple headmates that are stuck in the front. They are unable to switch with other headmates or go into headspace while they are frontstuck, but they can communicate with other headmates if they also come up to the front.
Switching/Switch
Switching happens when the current fronter(s) of the system changes. For example, if A was fronting, but switched with B, now B is fronting and in control of the body.
Co-Con/Co-Conscious
Being co-con refers to when multiple headmates are active at once. This is distinct from co-fronting in that these headmates aren't necessarily fronting, they may be in headspace or otherwise experiencing the outside world such as through internal communication.
Headspace/Innerworld
A headspace (also known as inner world or wonderland) is a place that members of a system can visit or inhabit, where they can talk to other headmates. Some systems have extremely detailed and intricate innerworlds, with planets, galaxies, countries, and more. While others may have something as simple as a room with a table and some chairs. Some systems don't even have an innerworld. It varies from plural to plural. However, having an innerworld is not just a plural-exclusive experience, as many singlets have them as well. The only difference is singlet innerworlds don't have headmates inhabiting them.
Singlet
A person who isn't plural, or in other words doesn't share their body with anyone else.
Splitting
Splitting is the process of the brain forming new headmates through external stress, usually breaking up an existing headmate into multiple (although the origins of some splits may be unknown). Anything can cause a split — violence, school stress, intrapersonal drama, abuse, flashbacks, etc. — and splits can cause one, two, five, or ten headmates from one event. A "split" may refer to the new headmate themself too.
Forming
Forming refers to any process that results in the creation of a new headmate. This usually is used in the sense of a non-stress induced creation of a headmate. This is also separate from a split because splits usually have the new headmate split "off" of an existing headmate, while a form may just come into existence on their own.
Introject/Introtive
Headmates who have an original source that their personality, identity, and memories may be based partially or fully on. These headmates may have memories from outside the body, or of things that did not happen to the current body (exomemories/"psuedomemories"). Some systems prefer to use introtive over introject, as introject is a medical term, so it's polite to ask which term they prefer.
For more on introjects/introtives, go here
Source
The material/media that an introject/introtive came from originally. For example, if a system has an introject of Deku, then that introject's source would be My Hero Academia. Or if a system has an introject of a Bucky Barnes, then their source would be the Marvel Universe.
Fusion
Fusion is the process of two or more headmates or fragments becoming one. The resulting headmate (sometimes referred to as a "fusion" themself) often has traits of both, but not always balanced. Fusing is not inherently bad or good, and can result in increased stability for the whole system; in the end, though, the choice to pursue large or small scale fusions is often a private matter and is up to every individual system.
Integration
Integration refers to the lowering of dissociative barriers, which may cause some headmates to fuse. Integration is often needed for fusion in disordered systems. Headmates who have integrated may have lower amounts of dissociative amnesia, which allows them to better talk, communicate, and memory share.
Dormancy
A state of inactivity during which a system member or group will be "asleep" for a certain amount of time. This is usually marked by difficulty in triggering them to the front, interacting with them or even finding them in the inner world, or experiencing their passive influence. Dormancy is very common in all kinds of systems, especially DID and OSDD ones.
Age-Sliding
Age sliding is when the age that a headmate feels or behaves as changes over time. Some age sliders have a static age that they slide up or down from, and others do not. Age sliders will often have a specific range that they slide between and can be large or small.
Age Cloudy
Age cloudy is a term for members in a system/collective that's age is cloudy/vague/fuzzy. They may have an age, but it maybe only slightly there, not solid or just a general range.
Fragment
A fragment is any headmate that usually does not possess full autonomy, sapience, or identity. These types of headmates may feel "incomplete" or "not fully formed".
NPC
An NPC refers to somebody within the headspace, who is not a headmate, but may be semi autonomous and interact with others exclusively within the headspace. They do not front, and may disappear when not being actively interacted with. NPC's are not a system exclusive experience, and singlets are able to make NPC's within their headspace, though somebody who is a system may have a more autonomous or interactive NPC.
Subsystem
A subsystem is a system within a system; oftentimes, when an individual member has a system or headmates of their own. This subsystem may have their own, separate place within the headspace, and may have their own system name separate from the main systems, and function as their own.
Sidesystem/Parallel System
A sidesystem is a separate group of headmates that exist, usually parallel/next to other systems within one larger plural body. There may be a "main system" that most of the common fronters come from, or all sidesystems may function equally. Sidesystems are larger in size than subsystems, and can have subsystems inside them as well.
Autopilot
Autopilot is a state some systems fall into when nobody is fronting. The body may continue to perform simple daily tasks by itself until a headmate returns to front. The complexity of those tasks and whether headmates are co-conscious with the autopilot varies from one system to another.


There are more terms than these, as the plural experience is very diverse, but this is just some basic terms you should know. If you'd like to know more about different terms plurals may use, make sure to check out the system types, system origins, and system roles sections!

Pluralkit / Discord Bots


Pluralkit is a bot designed to allow headmates to speak as themselves. It uses discord webhooks to create a ‘bot’ account with its own icon, name, and other information to assist systems in communicating more easily. It can be used by all types of systems and also allows itself to be used for kintypes or role playing. Adding this (or an alternative) bot to your server is highly recommended if you think or know systems will be there, and refusing to add a bot like this when asked can be seen as quite ableist as headmates deserve to be able to talk freely as themselves. Pluralkit can be indeed considered an accessibility bot, since it makes systems more capable to express themselves and their plurality freely.For more information on Pluralkit, or to add it to your server, go here

Introjects / Introtives


Introjects come in all shapes, sizes and forms. There is no limit to what a system can introject, and no system owes you any explination of why they've introjected a certain thing/person. It's personal to them, and can be considered rude, so be respectful.These are not all of the types of introjects/introtives there can be, but here are a good few:Fictives
Headmates based on a fictional source. Common sources are media like games and books, but almost anything can be a fictive's source, such as original characters or D&D characters created by other system members. Not all fictives act exactly like their canon counterparts, and it's considered 'rude' to treat them as if they are exactly the same unless they specifically tell you to.
Factives
Headmates that are based on a factional or non-fictional source, like another person. Sources can include celebrities, historical figures, friends, abusers, or anyone else. The source can be a singlet or a member of a system (including their own, or someone else's). Not all factives act exactly like their canon counterparts, and it's considered 'rude' to treat them as if they are exactly the same unless they specifically tell you to.
Fucktives/Faitives
A faitive is a system member that has traits of both fictive and factive. They may be an introject of somebody else's fictive, or they may be an introject of a fictional character that falls on the cusp of being real and fictional.
Fogtive
A fogtive is someone who is partially, somewhat, or almost a factive, but factive doesnt seem 'quite right' or 'entirely accurate'. Between or partially factive and something else (the something else may or may not be defined, personal choice).
Fuzztive
A fuzztive is someone who is partially, somewhat, or almost a fictive, but fictive doesn't seem ‘quite right’ or ‘entirely accurate’. The term is when someone is between or partially fictive and something else (the something else may or may not be defined, personal choice).
Songtive
A songtive is a type of introject whose source is a particular song, meaning they are essentially the embodiment of a song, or, a song in the form of a headmate. This often happens because the music brings great comfort to the system or makes them very happy.
Armstive
Armistive is a "fuck you" term that means that you don't need to know what type of introject a person is and what their source is.
???tive
???tive is when a system member knows they're outsourced in some way, but don’t know what that source is due to the source either not existing in this world or having not found it yet.
Clusterject
Introjects of a bunch of abstract thoughts thrown into one person (a few sentences or hyperfixations basically tossed into a pot and stirred together to make one person). Being an introject of a bunch of small things rolled into one.

System Types


Systems also come in multiple different shapes and sizes! While these are not all of the types, here are a few of the different types that you may come across:DID
Dissociative Identity Disorder (Previously known as Multiple Personality Disorder) is defined by the presence of two or more distinct headmates, switching between them, and recurrant amnesia between them (be it memory or switching amnesia). While a lot of documented DID systems are traumagenic, not every DID system is, and not everyone with DID calls themself a system. Trauma is not required to be diagnosed with DID.
OSDD-1a
Other Specified Dissociative Disorder 1a is missing the distinct headmates found in DID, but has the amnesia between them. OSDD-1a systems may be considered or label themselves as median, and may be more similar to each other than multiple systems.
OSDD-1b
Other Specified Dissociative Disorder 1b is missing the amnesia between headmates found in DID, but has distinct headmates. OSDD-1b systems may, however, experience something called emotional amnesia, which is a disconnect between headmate A's feelings towards headmate B's memory, despite the both of them remembering it.
P-DID
Partial Dissociative Identity Disorder is similar to DID, having distinct headmates and amnesia between switches. But P-DID systems rarely experience full/complete switches. Usually there is one dominant headmate which is fronting for most of the time, and one or more other non-dominant headmates that either passively influence the dominant headmate or go co-con with them. How often this happens is dependent on the P-DID system.
UDD/USDD
Unspecified Dissociative Disorder is when someone does not qualify for any other dissociative disorders [DID, OSDD, DP/DR, etc] but still exhibits disordered dissociative symptoms. USDD may also be used when the clinician does not choose to disclose more information about the dissociative disorder being diagnosed or is diagnosing quickly in emergency settings.
BPD System
A BPD system is one whose creation is influenced by Borderline Personality Disorder. A BPD system may, but not always, present as a median system. BPD systems may have headmates who's job is to handle [BPD] splits, and may have periods of blurriness and identity confusion much more often than other systems because of their BPD.
DPD System
A DPD system is a system who formed from having DPD, or Dependent Personality Disorder, and the need for headmates to help them with their needs and to take care of the body and tasks. These headmates may have jobs to help when the system needs a dependent, or when the system needs to be taken care of but cannot do it themselves because of their DPD.
Median
A median system (also called midcontinuum) is a system where members are not as distinct or separate from each other. It can be considered being somewhere between multiple and singlet. Some are dependent on a single individual, or the dependence can be mutual in that there is no central individual. Some median systems feel more blurred between themselves. Others may also be based around a shared identity or kin. The members of a median system are often described as aspects or facets, but it is still polite to ask what term they prefer.
Partitionary
A partitionary system is one where the divisions between headmates are particularly solidly defined. This may include other attributes, like lack of memory sharing, lack of internal communication, or lack of co-consciousness and resulting time loss.
Mediple
A mediple, or mediple system is a system that is decidedly both median and multiple. They may share closeness of mind, shared identity as each other, similar personalities, a single train of thought, or other characteristics, but distinctly identify as full-fledged and (semi-)separate people, and multiple in nature, despite not being partitionary by general means.
Multiple
A multiple system is the state of being more than one entity in one physical body where the identities of headmates are more distinct. This can often be used to include other attributes, like lack of memory sharing, lack of internal communication, or lack of co-consciousness and resulting time loss, but partitionary is in fact a better descriptor for such experiences, as multiple describes identity and not memory.
Mixed/Chimera/Hybrid
Mixed system refers to a system with both median and multiple headmates; a system that is a mix between median and multiple.
Some synonyms are Hybrid (System, Plural, Etc) and Chimera (System, Plural, Etc).
Gateway
A gateway system is one in which the inner world is perceived as a real place somewhere, or a (usually) large system with members predominantly from, often coming or going as they please. These systems may have gates (an object or passageway that exists in a system's inner world that leads to other locations) or may have lots of walk-ins. (a headmate who comes from elsewhere in the inner world or another world other than outer world)
Dreamway
A dreamway system is a type of gateway system. The primary distinctive aspect of such a system is its particular structure; possible worlds to be accessed are comprised of daydreams and paracosms. There is no limit to the amount of paracosms systems may be able to access. Each world may exist on varying levels. A dreamway system is typically resulted by the having of Maladaptive Daydreaming Disorder or other strongly present neuronarrative qualities.
Polyfragmented
Polyfragmented systems have large amount of fragments. The exact number of fragments required varies from source, but the most common definition is 100+, although this is misleading. Commonalities among polyfragmented systems are; Complex internal structures like subsystems, sidesystems, and layers, Active and detailed inner worlds, Co-consciousness being more frequent, A relatively small fronting group, Splitting and forming easily, both with or without trauma, and splitting multiple fragments at once, A number of "well defined" alters that may be similar to non-polyfragmented systems
Polyastro/Astro
Astro refers to having an infinite/nearly infinite amount of system members. While PolyAstro refers to a system with infinite/nearly infinite headmates, and several groups/areas (subsystems, sidesystems, layers, etc). PolyAstro systems might have a gateway/dreamway etc, where headmates come and go between.

System Origins


There are multiple different reasons that systems can form, and origin labels help systems with putting a name to what formed their system. However origin labels can also apply to individual headmates, as not all headmates will have the same origin.These are some common origin labels in the plural community:Traumagenic
A system that originated or formed from trauma. This can be any kind of trauma, at any time in a system's life, not just their childhood, and not just repetitive.
Endogenic
A system that formed without trauma. This is an umbrella term for ANY system that wasn't formed from trauma, but not every system that wasn't formed from trauma wants to use the term endogenic.
Neurogenic
Systems that formed as a result of their neurodivergence, or from a mental illness. Usually, headmates originate from the need to cope, or be introjects based off symptoms like hallucinations or hyperfixations. Neurogenic systems may or may not disclose the specific disorder or neurodivergence they have.
Protogenic
A system which has existed from birth, has never had a noticeable singlet phase, or cannot remember their formation. This system may have been born with their headmates, and grown up with them, or they may have gone through "phases" of "evolution" and change.
Parogenic/Willogenic/Tulpamancy
Systems or headmates that were purposely created using thought-based or metaphysical means. There has been a lot of discourse around the use of "tulpamancy" and "tulpas" as the concern that the terms are culturally appropriative has been brought up, so alternate terms such as Parogenic and Willogenic have been coined. However, the discourse of the label tulpamancy is something for you to dig into yourself to get your opinion on. [if you are a system]
Metagenic
Metagenic systems are ones that formed with metaphysical or spiritual origins not necessarily tied to any religion or practice.
Spirigenic
Spirigenic refers to systems that were created for or through religious or spiritual means.
Mixed Origins
Mixed origin refers to a system that has multiple different system origins. This could be because their system formed from a combination of factors, or that not all of their headmates are of the same origin.
Agenic
Systems who don't identify with any origins/view their system as not having any origins.
Pangenic
Pangenic systems are ones that have all origins within their experiences. For example, a system cannot have spiritual origins of a religion they do not practice. This can include systems who have all origins that they are aware of instead of all existing origins (still within their experiences).
Quoigenic
An origin term that means the user does not want to share their origins, does not think it's relevant, or thinks it's the wrong question to ask.
Praesigenic
Praesigenic is a system origin term that means a system doesn't want their origin known, or doesn't want to tell that specific person. It's intended as a "fuck you" to the person asking. This can be for any reason, including safety or spite.
TraumaEndo
A TraumaEndo, or trauma-endo, system is a mixed-origin collective with both traumagenic and endogenic origins, used to focus on the unique problems and experiences of systems with both of these origins. These experiences can include being told that all system members must be traumagenic, or all must be endogenic; not feeling comfortable in the traumagenic community, endogenic community, or both; being disordered without a traumatic origin; etc.

Exomemories / "Psuedomemories"


Exomemory is a general term for memories that the body did not experience. Often found with sourced members (such as introjects), but not exclusive to them. It can also be experienced by singlets, including kin and immersive daydreamers.For example, if you have an introject from a source that has wars or battles, they may remember being on the battlefield, fighting, or remember the affects of the war on their home, despite none of those things happening to the body that they are currently in.Exomemories are just as valid as bodily memories, as they can affect a headmate the same way bodily memories can.This is not to say that every sourced member experiences exomemories, though.Medically, people have used the term "psuedomemory" to describe this experience, despite the two words having different meanings. A psuedomemory is a fake memory, such as a spurious recollection of events that never took place, as opposed to a memory that is merely inaccurate.Exomemories are not fake memories, they are just memories that did not happen to the current body or in the outer world.However, some systems prefer to use the term psuedomemory over exomemory, so it's always polite to ask which term they prefer.

System Roles


There are many different roles that headmates in a system can have, and some headmates have more than one role they perform.Here are a few of those roles:Core
The core is a headmate with a direct connection to the body's pre-plural self. Not every system has one, and not every system had a point at which they were not plural.
Host/Outernaut
A host is the headmate who is most active, most responsible for day-to-day activities, or otherwise is fronting most often. Not all systems have hosts, and some may have a rotating team for the role. In addition, some do not like the term "host", and choose to use alternatives; specifically, outernaut.
Co-Host/Perinaut
A co-host is a headmate that shares the duties of day to day fronting with other members of the system. They may be secondary to a primary host, or equally share the role between multiple members.
Protector
A protector is a headmate whose role is to protect other members of the system from external harm, traumatic memories, harmful members of the system, or other threats. Any system can have a protector, traumagenic or otherwise.
Persecutor
A persecutor is a headmate who acts harmfully towards other system members, the body, or to others. It's common for this to be out of a misguided attempt to protect the system or themselves. Persecutors often hold internalized trauma, shame, and/or guilt, and act in reaction to it, and the harm they cause may be unintentional. All persecutors deserve kindness, patience, and the chance to work through their problems just like any other headmate. Causing harm does not make them any stronger, less distressed, nor does it mean they have less needs than other headmates.
Protescutor
A protescutor is a headmate who would technically be a prosecutor/persecutor otherwise but they and/or their headmates don’t feel it totally fits or don’t like the connotations. Usually, a headmate who "isn’t as much of a jerk" as prosecutors/persecutors are seen as. Can also be used for headmates who are both persecutors and protectors.
Caretaker
A caretaker is a headmate whose role is taking care for or assisting with the system or other headmates. They may sooth, guide, or help process emotions for system members, including individual headmates, groups, or the system as a whole. Some caretakers look after the the body by keeping up with hygiene or going to work. They may struggle with their own emotional wellbeing and self-care.
Worrier
A worrier is a headmate that often worries for the worst, even if it's unintentional. They often focus more on the bad than the good, even sometimes finding bad in things that are primarily good. They don't want to disrupt the system, but sometimes their over-worrying can do that.
Dissonaut
A dissonaut is a headmate that holds or experiences intense dissociation. They may numb the body or cause the body to dissociate upon fronting.
Trauma Holder
A trauma holder is simply any headmate that holds significant trauma, often to keep others within the system safe from that knowledge. They are more common in traumagenic systems, but are not exclusive to any specific origin.
Symptom Holder
A symptom holder is a system member who holds symptoms of the body's neurodivergence, mental illness, etc. A symptom holder may hold certain/specific symptoms, multiple symptoms, or all symptoms.
Memory Holder
Memory Holders are system members that hold specific memories, which may not be easily accessible to other members. These memories may be about trauma, specific people, locations, or life stages. Memory holders may also be trauma holders.
Little/Syskid
A little/syskid is a headmate that behaves or otherwise feels like they are a young age. This often approximately caps at age twelve, but may vary personally between systems based on their body's age.
Middle/Systeen
A middle is a headmate that behaves or otherwise feels like they are teen-age, often capping at age 17. Tweens may also be included in this.
Big
Big refers to a headmate who behaves or feels like an adult. While the exact age of a big is often related to the age of the system's body, it is generally at least 18 years old.

Misconceptions


There are many misconceptions and stereotypes regarding plurality that are harmful to the plural community as a whole. Some of these stereotypes and misconceptions will be listed below, with the truth about them underneath.Theres an "evil" or "killer" alter
This is one of the most harmful, and common, stereotypes out there. That there is an headmate who is some sort of serial killer. That couldn't be further from the truth. The chance of an headmate being a serial killer, is about the same as any other person being a serial killer. Headmates are not inherently evil, and the insinuation that someone who is plural is dangerous is rooted in ableism.
Headmates cannot die
This is extremely relative to how the system in question works. No two systems are the same. The brain is capable of things we could never fathom. If your system functions in a way that allows headmates to die, then they can. If you systems functions in a way they cannot die and simply go dormant, then they can't. Saying that headmates can't die at all for every system is ignoring the systems who have spent months or years mourning their lost headmates. Or those who are still currently mourning. This is not to say that you should try to kill your headmates just to see if they can die, but just keep an open mind when discussing or thinking about this topic.
System travel is only for spiritual systems
We (Cafe Equinox, the authors of this carrd) can understand where this belief may come from, but it's just not true. System travel is the practice one or more headmates leaving their system to go to another one. This is recommended to only be practised with systems you have extreme trust in, and whom you have discussed boundaries thoroughly with, as there ARE risks to it (as there are with everything).
But many people think that this practise is only for spiritual or gateway systems. System of any origin or type can practise this, though some types may have an easier time than others. But as with all skills, the more you do it, the better you will become at it.
Integration/fusion kills headmates
Integration does not, in fact, kill the headmates that integrated. It just merges the personalities of the two headmates to create somebody new. They are not truly 'dead'. Just different now.
Integration/fusion "cures" plurality
Final fusion / Complete integration is often seen as the end all, be all of therapy and treatment regarding plurality. This is simply untrue. Many systems decide they never want to fully integrate or fuse, and rather go for functional plurality, where all alters co-exist and function together.
Switching is super obvious
Switching can be very dramatic and obvious, but not always. You may not even notice that the system you know has switched unless they outwardly tell you. A lot of plurality, at least in regards of DID/OSDD, is very covert. It's possible for switches to occur mid sentence without the other person in the conversation noticing in the slightest.
Fictives are/are not their source
A fictive is, at the end of the day, a fictional introject. Some fictives are nothing like their source, and others are extremely like their source. It's rude to make assumptions about fictives. At the end of the day, a fictive is their own person and it's improper to treat a fictive like just a "character" and not their own person. But some fictives identify heavily with their source and would be very upset if treated like they're not themselves. It's best to ask a fictive their own personal comfort on this manner
System Resets/System Collapses
A system collapse is when a system loses a large number or even all of its headmates in a short span of time. This may be due to trauma or other stressors, although some systems may experience periodic collapses naturally, as part of how their system functions.
A system reset refers to the resetting of a system. This means the system having a start over of sorts, ranging from collapsing and becoming a system again, or just reorganizing how things are managed.
These two terms are hotly debated in plural spaces, as multiple people do not believe they are possible. Or, if they do think it's possible, they don't believe it can happen to traumagenic or disordered systems. Which is, again, simply not true.
Referencing back to headmate death, some systems (such as ourselves) who have gone through system collapses have spent months mourning their lost headmates, wishing they could return, just as a singlet would mourn a dead loved one. And a lot of people like to argue that these lost headmates have just gone dormant, and that using these labels are harmful.
In the end, these terms are self-identifiers. No one is forced to use these labels, they are here to be used if a system would like. If they would not like to, then they do not need to. You don't need to dissect and invalidate a system's experience just because of your personal opinions about how systems work.

Common Courtesy


It can be hard to know what is and is not appropriate to do with systems. This will explain the general rule of thumbs, but this is not the end all be all. Some systems are okay with things that others are not.Do not assume each headmate is the same
The most important thing to note is each headmate is a different person. Treating an headmate like another headmate, is generally frowned upon and can be seen as very disrespectful, if not downright ableist. Respect their different names, pronouns, behaviours, preferences, and treat them like the different people they are.
Do not assume that all headmates had a choice in who they are
Do not tell a fictive or introject that their source is 'problematic' and that they are wrong for existing. That is cruel. Nobody is wrong for just existing, no matter what they are sourced from. Treating them as evil for simply existing is wrong on so many levels.
Do not trigger out a headmate without explicit consent
If you know a headmates front trigger and you want them to front, you do NOT front trigger them without explicit consent from the current fronter and the headmate you're trying to trigger out. Especially if the front trigger you know is a negative trigger. Do not use a negative trigger unless it is an absolute emergency on the system's end.
Do not assume systems are roleplaying
A lot of people assume that systems and plural people are simply 'roleplaying', especially involving fictives. We are not roleplaying, we are different people, and insinuating that we're just roleplaying is ableist.
Do not assume introjects want to roleplay as themselves
Some introjects are very uncomfortable with the insinuation of roleplaying as themselves. They are not simply just a character to play around with, they are a living, breathing, person.
Do not assume you would be able to "tell" if someone was a system or not
Systems can be very covert. You can not always tell if somebody is a system, and if somebody tells you they are one, do not tell them that you would "know" if they are one or not.
Do not make jokes about those use Pluralkit being bots
We've heard it a million times. It's not funny. It was never funny.