I have been searching for a treatise on "representation" of people, things, etc.

It seem that you must have the ability to think in the "abstract" to comprehend that people can be represented as well as things. Michael Joseph has made excellent points that you must have a fundamental comprehension of trusts, and how trusts are derived from relationships. I think that a to understand relationships, you must also have to be able to understand that you can have a relationship through an agent, and as a principal, that agent represents you.

If you have any leads, please let me know.