Multiplicity is perhaps the most interesting personality variation known of all conditions that have a primarily psychological basis.  Multiplicity has been called Multiple Personality Disorder, and has most recently been known as Dissociative Identity Disorder.  For purposes of discussion in this chapter, we will refer to the condition using the medical term Multiple Personality Disorder when referring to the condition from the viewpoint of the medical profession.  Otherwise, the more accurate term multiplicity will be used.  The newer term, Dissociative Identity Disorder, is a meaningless term and misrepresents what the condition actually is.

Multiple Personality Disorder is considered a mental condition in which two or more distinctly identifiable personalities exist within the same person.  Each personality is expressed at different times, but not simultaneously.  The defining feature is a significant degree of identity alteration.  When a personality switch occurs, the person will exhibit different behaviors, personality traits, thought patterns, and cognitive abilities.  Mutual exclusion of the characteristic personality traits of each identity is also seen in Multiple Personality Disorder.  Distinct memories associated with each personality are also characteristic of Multiple Personality Disorder.  This mutual exclusion of memories is seen to varying degrees in both the long term and short term memory of the affected person.  The person, therefore, often will not remember what transpired when another personality was in control.  As a result of different memory sets, the person with Multiple Personality Disorder will have separate sets of life experiences.

The question of whether multiplicity is an actual disorder or an invented one has been under question in recent times.  Enormous amounts of medical research support the existence of Multiple Personality Disorder.  Electroencephalogram (EEG) studies support the theory of the potential existence of multiple personalities in one person.  Sufficient objective and subjective evidence is submitted by researchers that clearly support the existence of the condition.  The opinions put forth by decades of research, for some reason, have been ignored in favor of the unsubstantiated opinion that the disorder is of a questionable existence.  Since no medical treatment for Multiple Personality Disorder can be offered, the physician who diagnoses the condition has essentially put forth a dead end diagnosis.  The medical profession has no pill to prescribe, no body part to extract, and no brain surgery that can cure the condition.  Any treatment, therefore, is limited to non-medical protocols.  With no medical treatment available, it is easily understood why the existence of the condition is under question.

If we examine the concept of multiplicity, we have a well-defined collection of clearly related personality characteristics.  Clearly identifiable characteristics associated with the same condition, which are observed to occur in a definable segment of the population, simply does not occur by chance.  When something does not occur by chance, yet cannot be clearly proven, it is nothing more than concrete evidence the cause has not been found.  A problem arises, however, when we believe that a cause, in every case, must exist.  No consideration is given to the possibility that multiplicity is a natural condition and therefore has no cause.  The characteristics associated with multiplicity are very specific.  Furthermore, the experiences described by patients reflect high specificity and great reliability.  The condition cannot be simulated or faked even by the most knowledgeable individual.  Logic, therefore, must lead us to conclude that we have a clearly defined condition.  If we have a clearly defined condition, it cannot be simply dismissed as nonexistent.

Multiplicity was a relatively unknown condition until 1980.  Before that year, approximately 200 cases of Multiple Personality Disorder were reported.  After 1980, the number of reported cases is found in the tens of thousands.  This figure does not take into account any undiagnosed cases.  Multiplicity appears to be more prevalent in the United States of America.  The question arises, then, what has changed since 1980 to cause such a dramatic increase in persons capable of multiplicity.  In addition, the question arises about what is unique to the United States of America to account for the disproportionate number of cases when compared with the rest of the world.