The Harmonic Groups (or triads) were discovered by Don Riso and further disseminated by Russ Hudson, Riso's business partner. Each group reveals a patterned approach to challenging topics or personal and professional conflicts. Each Harmonic Group has three subtle variations, depending on the Point in question. The Rational Competency Group includes Points 1, 3, and 5. The Positive Outlook group includes Points 7, 9, and 2. The Emotional Realness group includes Points 4, 6, and 8. 

The Hornevian Groups (or triads) are based on the Hornevian Model, named after Karen Horney, who discovered that people interact with others in specific energetic and predictable ways to meet their needs. Horney did not correlate her model to the Enneagram system; however, Enneagram research found alignment between the two. Thus, the Hornevian Groups were established. The three Enneagram Hornevian Groups are broken down into the Compliant Group (Points 1, 2, 6), the Withdrawn Group (Points 4, 5, 9), and the Assertive Group (Points 3, 7, 8).

Our triggers and responses can be obscure and are often mismatched with the patterned defense system of the other person, Hornevian and Harmonic—generating dissonance. Additionally, if we're unaware of our patterns, parallel strategies will undoubtedly cause strife. So if a client (or another human) says or does something that triggers us, we undeniably respond in a manner aligned with one of these Hornevian and Harmonic Groups. 

In my book, Witnessing Grief, you can learn more about the Harmonic Groups.
In Personality Types, by Don Riso and Russ Hudson, you can learn about both the Harmonic and Hornevian Groups.

Holly Margl is the award-winning author of Witnessing Grief; Inviting Trauma and Loss to Our Coaching Conversations, An Enneagram Perspective, coach, coach mentor, and trainer specializing in grief, trauma, and the Enneagram.