E/I Dichotomy (Extraversion/Introversion) is the first of four scales in the Myers-Briggs typology (MBTI, #4) and in Socionics (#8), defining the direction of psychic energy: outward (Extraversion) or inward (Introversion).

Origin

Jung is the source. Introduced by Carl Gustav Jung (German Carl Gustav Jung, "Psychologische Typen", 1921). Jung defined E/I not as sociability vs reserve, but as the "direction of the movement of libido".

Definitions

• Extravert (E, Extraversion) — energy flows toward the object, orientation to the outer world
• Introvert (I, Introversion) — energy returns to the subject, orientation to the inner world

Interpretation Differs Across Systems

MBTI (#4). E/I is a preference, self-report, a spectrum. A person can be an "ambivert" sitting in the middle of the scale.

Socionics (#8). E/I is an objective trait that determines the sign of the leading function. Extravert = leading function is black (extraverted), introvert = leading function is white (introverted).

Big Five (#3). E/I is Extraversion as one of five continuous factors (not a dichotomy, but a spectrum from 0 to 100).