The nine Enneagram personality types by themselves don't adequately describe the variations in personality. Additional concepts have been added to the system over the years in an attempt to do this (e.g., wings, instincts, Tritype). This book describes these concepts and the many variations of type that result from applying them to the nine types.
This book, the 2nd planned book in the Enneagram User Guide series, is currently being written. Expected publication is spring 2018.
The Enneagram symbol was first introduced to the world by G.I. Gurdjieff near the beginning of the 20th century. He didn't use the symbol with personality. Instead, he used it to understand processes. This book makes a clear distinction between how Gurdjieff used the symbol and how the types use the symbol and explores how the symbol can be used to better understand and gain insight into the types.
This book, the 3rd planned book in the Enneagram User Guide series, is currently being written. Expected publication is fall 2018.