Raoden's memory of Ien at the beginning of this chapter pretty much sums up what the seons are. A lot of readers have asked me for more on them, and I'll give it eventually. However, in this book, you simply need to know that they are what they appear. Servants bound out of love, rather than duty, force, or pay.
The original inspiration for seons came, actually, when I was in high school. Visually, I was inspired by the Passage series–a collection of paintings by Michael Whelan. Every painting in the series contained little floating bubbles with what appeared to be a candle flames at their center. At the same time, I was getting the idea for a story. When I wrote it, I included a group of sentient balls of light.
Well, that story didn't go anywhere. Six years later, however, I started Elantris. I wanted a sidekick for Sarene, and I knew I needed someone wise and cautious to off-set her sometimes reckless personality. I had already decided to use the Aon characters, and I considered transforming my old idea of balls of light into glowing Aons. As Ashe's character began to develop, I realized I had something quite strong, and I began to build the mythology and magic behind the seons.
The latest addition to the story regarding seons is the idea of "Passing." I only speak of it a few times, but in earlier drafts, I didn't have any definite indications that a person and their seon were bound. The only hint was what happened to seons whose masters were taken by the Shaod. When Moshe asked about this, I decide I'd include a little more information, and added a couple references to "Passing" seons in the book.