The enneagram figure is usually composed of three parts; a circle, an inner triangle (connecting 3-6-9) and an irregular hexagonal “periodic figure” (connecting 1-4-2-8-5-7). According to esoteric spiritual traditions, the circle symbolizes unity, the inner triangle symbolizes the “law of three” and the hexagon represents the “law of seven” (because 1-4-2-8-5-7-1 is the repeating decimal created by dividing one by seven in base 10 arithmetic). These three elements constitute the usual enneagram figure.
Each of the personality types is usually understood as having three “instinctual subtypes”. These subtypes are believed to be formed according to which one of three instinctual energies of a person is dominantly developed and expressed. The instinctual energies are usually called “self-preservation”, “sexual” (also called “intimacy” or “one-to-one”) and “social”. On the instinctual level, people may internally stress and externally express the need to protect themselves (self-preservation), to connect with important others or partners (sexual), or to get along or succeed in groups (social). From this perspective, there are 27 distinct personality patterns, because people of each of the nine types also express themselves as one of the three subtypes. An alternative approach to the subtypes looks at them as three domains or clusters of instincts that result in increased probability of survival (the “preserving” domain), increased skill in navigating the social environment (the “navigating” domain) and increased likelihood of reproductive success (the “transmitting” domain). From this understanding the subtypes reflect individual differences in the presence of these three separate clusters of instincts.
It is generally believed that people function in all three forms of instinctual energies but that one usually dominates. According to some theorists another instinct may also be well-developed and the third often markedly less developed.