Through the course of western thought, different theories have been put forth to explain the human personality:
Sigmund Freud broke the human personality down to three significant components: the id, the ego, and the superego. Personality is shaped by the interworkings and conflicts of the three.
Katherine Briggs and her daughter Isabel Meyers alleged that the writings of Carl Jung delineated personality types.
B. F. Skinner, a proponent of behaviorism, suggested that the human personality is developed through external stimuli.
Holland proposed a "RIASEC" model of personality widely used in vocational counseling. The RIASEC is a circumplex model where the six types, which are represented as a octagon where physically closer types are more related than distal types:
Typologies or type models arise naturally from some theories that posit types of people. For example, astrological signs represented a well-known, pre-scientific typological model. Typological models posit a relatively small number of modal types and possibly some interaction between the types. The Jungian typology implemented in the MBTI may best represent the typology approach.
Circumplex models may resemble factorial or type models but further specify a relationship between the different types or factors. Typically, some types or factors are more related than others and can be presented on a polygon. Holand's RIASEC may be the best-known example of this type of theory. Correlations of personality scores should resemble a simplex form where opposing types have low correlation and close types have a high correlation.
