Advanced Concepts
The personality types are grouped into "triads." 2, 3, and 4 are in the Heart Triad; 5, 6, and 7 are in the Thinking/Head Triad; and 8, 9, and 1 are in the Instinctive/Gut Triad. The personalities in each of these triads are usually making decisions based either on relationships and emotions (Heart Triad), logic and mental processes (Thinking Triad), or gut and action-oriented processes (Instinctive Triad). Read the full description for a full understanding of the triads.
There is also a more subtle element of the Enneagram personality theory called a "trifix." It basically states that your personality may be subtly influenced not only by your primary personality type, but also by two other personality types in the opposing triads. So if you are a type 4, which is in the Heart Triad, but you also identify strongly with the description of a type 6, which is in the Head Triad, and you notice yourself consistently acting much like a type 1, which is in the Instinctive Triad, then your trifix will be something like 4/6/1. Type 4 personality characteristics are your ego's "primary fixation" and type 6 personality characteristics are you ego's "co-fixation," while type 1 personality characteristics also provide a frame of mind for your ego to become fixated on.
One quote explains the nature of the trifix this way: "The Ego is like a fearful entity living inside the nine-sided house who becomes convinced that the outside is dangerous and that it is most likely to see and be able to respond to this perceived danger by looking through three particular windows. Because the Ego is very fearful, it spends a great deal of time fixated on the view through these three windows. It may set up chairs with binoculars in front of these windows; it will become very familiar with these three particular views. Every time the Ego feels particularly or suddenly threatened, it will immediately go to these windows. The Ego is Fixated in these three Domains. "
Of course, the trifix is a smaller aspect of the Enneagram theory and should not concern you if you are only just starting to determine your type. Only later when you notice some consistent characteristics in yourself which are similar to personalities in other triads should you become interested in finding out your trifix.