According to the Jung - Myers-Briggs typology all people can be classified using four criteria:
Extroversion - Introversion, Sensing - Intuition
Thinking - Feeling, Judging - Perceiving
Different combinations of the criteria determine a type. For example:
ISTJ - Introvert Sensing Thinking Judging
http://www.humanmetrics.com/cgi-win/JTypes1.htm