The Enneagram is a personality model built on a nine-pointed figure, and the figure does analytical work rather than decorating the model.
Nine types are numbered and commonly named: the Reformer or perfectionist, the Helper, the Achiever, the Individualist, the Investigator, the Loyalist, the Enthusiast, the Challenger and the Peacemaker. Each is defined not by behaviour but by a core motivation, a basic fear and a basic desire, which is why two people of the same type can behave quite differently and why the system resists questionnaire diagnosis more than most personality instruments.
The figure supplies three further structures. Wings: each type is shaded by one or both of its neighbours on the circle. Lines of integration and disintegration: the internal lines connect each type to two others, and practitioners read a person as taking on the qualities of one under stress and the other in growth. And the centres: the nine group into three triads of three, body or instinct at eight, nine and one; heart or feeling at two, three and four; head or thinking at five, six and seven, each with a governing emotion, anger, shame and fear respectively.
Most schools add instinctual subtypes, self-preservation, social, and sexual or one-to-one, giving twenty-seven variants, and levels of development describing how healthily a type is being lived.
What practitioners claim for it is self-knowledge: that identifying a habitual motivational pattern makes the pattern visible and so loosens it. Determining one's own type is treated in most schools as a process of extended self-observation rather than a test result, and the published questionnaires are generally described by their own authors as indicative only.