Fundamental to the Myers-Briggs Type Indicator is the theory of psychological type as originally developed by Carl Jung. Jung proposed the existence of two dichotomous pairs of cognitive functions:
* The "rational" (judging) functions: thinking and feeling
* The "irrational" (perceiving) functions: sensing and intuition
Jung went on to suggest that these functions are expressed in either an introverted or extraverted form. From Jung's original concepts, Briggs and Myers developed their own theory of psychological type, described below, on which the MBTI is based.
The Myers-Briggs typology model regards personality type as similar to left or right handedness: individuals are either born with, or develop, certain preferred ways of thinking and acting. The MBTI sorts some of these psychological differences into four opposite pairs, or dichotomies, with a resulting 16 possible psychological types. None of these types are "better" or "worse"; however, Briggs and Myers theorized that individuals naturally prefer one overall combination of type differences. In the same way that writing with the left hand is hard work for a right-hander, so people tend to find using their opposite psychological preferences more difficult, even if they can become more proficient (and therefore behaviorally flexible) with practice and development.
The 16 types are typically referred to by an abbreviation of four letters—the initial letters of each of their four type preferences (except in the case of iNtuition, which uses the abbreviation N to distinguish it from Introversion).
http://en.wikipedia.org/wiki/Myers-Briggs_Type_Indicator