I subscribe to the theory that we all have multiple personalities. For healthy people, there is a relatively seamless transition from one personality to another, which requires active observation to notice. Under stress, the extremes of our different "selves" become more noticable. In some very unhealthy people, the personalities have become disassociated from the core Self - this is what is commonly known as Multiple Personality Disorder.
There is a school of thought in the MBTI community that each of our eight type functions is intimately linked to a specific internal Jungian archetype. According to this school, it is impossible to use a function without invoking its associated archetype. Therefore every person has at least eight different "personalities", since we generally have to use all 8 functions in our lives (some more than others, of course). The archetypes and functions are as follows:
Primary Processes
We can consciously control these through development and use.
1. Dominant/Hero/Heroine/Leading - organizes adaptation; initiates individuation; has our complete trust. Can become overbearing and domineering if over-used. We have the most conscious control over this function and energy costs for using this function are low.
2. Auxiliary/Father/Mother/Supporting - Supports and nurtures dominant function; sets standard of perfection; how we are helpful to ourselves and others. Can be overprotective and smothering. More energy costs than the dominant function, but still relatively low.
3. Tertiary/Puer/Puella/Relief - the playful and vulnerable child; moderates the purposefulness of the dominant and auxiliary functions allowing the person to lighten up and relax; how we express our creativity and improvisational skills; unsettling to others; high energy costs.
4. Inferior/Anima/Animus/Aspirational - gateway to the unconscious; last function we have conscious control over; source of ideals that are difficult to live up to; sense of purpose, inspiration, and change; likely to look immature when using this function; high energy costs.
Shadow Processes
These are usually experienced negatively and are beyond our conscious control. All have high energy costs.
5. Opposing - defends by offending, seducing, or avoiding, provides self-critiquing; refuses to play by the rules; serves as a passive or aggressive adversary to the Hero/Heroine of other people; can provide backup for one's own Hero/Heroine.
6. Critical Parent/Witch/Senex - finds weak spots in ourselves and others; appears under extreme duress; seeks to discourage, cast doubt, set limits, and belittles; is authoritarian and stern; can be the source of new discoveries.
7. Deceiving/Trickster - mischievous, wreaks havoc, circumvents obstacles, petulant; is not trustworthy when seen in other people; fools us into thinking something is important to do or pay attention to; compensates for the trust of the puer/puella and insulates against the cruelties of the world; is often the source of our sense of humour.
8. Devilish/Demon/Daimon - destructive to ourselves and others, undermines, often erupts violently; distorts trust in relationships, promotes chaos; can be powerfully transformative.
As an INFJ, the order of my functions according to this hypothesis is:
1. Ni
2. Fe
3. Ti
4. Se
5. Ne
6. Fi
7. Te
8. Si
My personal experiences with my own processes, as well as those of people whose type I know very well, has convinced me that this is an accurate description of how the functions operate in at least some people. Each archetype may be personified in our dreams, and some of its traits may come to the surface when we are using a function. For example, the Anima is the female aspect of a man. Under stress, a man's voice may become more feminine (eg. rising noticably in pitch - I certainly do this!). This is supposedly a sign that the Anima has been invoked. Females may do the opposite - a throaty deep-pitched growl as their masculine Animus rises to the surface.
See this thread for more info:
http://www.typologycentral.com/foru...ality-matrices/1416-archetypes-functions.html