A black diamond examination of the intersection of these two systems.

What function do they serve? Sandra Maitri offers answers in her book The Spiritual Dimension of the Enneagram.

What does it mean to actually "think"? How often do we do it?

Sixes question authority, look for guidance, play in established musical styles and defend the underdog.

Fives are perceptive, cerebral and secretive. In music, they're often innovative, hugely original and have a love of technology and unusual instruments.

Enneagram Fours are feeling based, sad, different, determined to forge a unique and authentic personal identity. 

And what does this say about the human condition?

A look at Chicago based musician Andrew Bird: violinist, guitarist, singer, whistler, loop pedal magician and subject of the new concert documentary Andrew Bird: Fever Year.

The Enneagram charts nine personality types in the human race, but it also has profound spiritual ramifications, as Sandra Maitri explores in her book on the subject.

Enneagram Personality Type Three is the Performer, the Achiever, the Catch, the Best. Exemplified in this case with Madonna and William Shatner.

The Enneagram's personality Type Two is the Helper, the Giver, the Special Friend. Here's what they look like in action. In the world of music.

Take a great big drink of righteousness with two songs that bring to life the Enneagram personality system's type One: the Reformer. 

Barbara Ehrenreich's book Brightsided analyzes America's obsession with success and positivity. This coincides with the Enneagram personality system's type Three: the Achiever. So what happens when one type's values dominate a culture?

Our culture trumpets certain personality traits and discourages others. But are those standards absolute or relative? How would our society look if we accepted the rightness of there being essential differences between our various points of view? At the same time, it would bond us to know how strongly similar so many of us are.