Having an engineering background, I could see a concrete example of Plato's Divided Line that supplements the explanation provided by Dr. Roochnik. The example is based on television.
Plato's Republic on CD
Plato's Republic is a dialog. The best way to study it is to hear it. I recommend the complete Republic on CD, from Agora Publications. Buy the book from Agora as well and you can follow along with the dialog.
Plato: a Life Changing Experience
Augustine of Hippo, in his Confessions, said Cicero and Plato helped prepare him for Christianity. Great people from the past have had their lives enriched by studying Cicero and Plato. But it is not only in the past that lives are changed by Plato or Cicero.
The September 21, 2008 issue of the New York Times Magazine ran an article, The Thinker by Jonathan Mahler, profiling Dr. Kelly Jolly of Auburn University. The article says Jolly was a precocious student in high school, so one of his teachers gave him Plato's Dialogs to read. From the article:
“Until then, I’d been clever enough to do whatever I wanted to do, to read with one eye,” he told me. “Then all of a sudden I ran into philosophy, and it was like running into a brick wall.”
Kelly Jolly found a Plato challenging, but he stayed with it and it changed his life. He became a professor of philosophy. Reading Plato is a challenge, but it is worthwhile, enriching, and potentially life changing.
Plato, Cicero, and Our Roots
The Great Learning says,
"Things have their root and their branches. ...It cannot be, when the root is neglected, that what should spring from it will be well ordered." (Legge)
Another translation puts it, "It is impossible that the root be unhealthy and the branches healthy." (Gardner)
The ancient Greeks and Romans are the roots of Western civilization. America cannot be a healthy republic if we lose touch with our roots, which I believe we have done.
It is no coincidence that American power, reputation, and prosperity has collapsed during the last eight years. America is crippled because it has lost touch with its roots. We need to nurture our roots by studying and applying the best lessons of our heritage. Plato and Cicero are a good starting point.
Plato's Republic and Adult Continuing Education
Adults who enjoy continuing eduacation can make use independently of the commercially available materials from The Teaching Company and Agora Publications. But those adults who would enjoy a group study of The Republic can consider the suggested syllabus at this link.