The MBTI identifies a position along a spectrum for four sets of opposing qualities. The first letter is either I or E reflecting a preference toward Introvert and Extrovert. The second letter is either N (for Intuitive) or S (for Sensing). The third letter represents the spectrum from T (Thinking) to F (Feeling). Finally the fourth letter is either J or P (Judging or Perceiving). So an INTJ type would be one with a preference for Introversion, Intuition, Thinking, and Judging.