All is Revealed
THE DIVIDING LINE
Plato took Socrates' maxim "virtue is knowledge" and extrapolated it into an elaborate theory of knowledge. "Take a line divided into two unequal parts, one to represent the visible order, the other the intelligible, and divide each part again..." With these words, Plato introduces his concept of the dividing line between opinion, whose objects are in the visible world and knowledge, whose objects are in the intelligible world and exist as ideas or forms. He also creates a mental image of a ladder of knowledge which the philosopher ascends in his search for truth.
"In the world of knowledge, the idea of the Good appears last of all, and is seen only with an effort; and when seen, is also inferred to be the universal author of all things beautiful and right, parent of light and the lord of the light of this visible world, and the source of truth and reason in the intellectual."
from "The Republic"
The supreme Form, and the ultimate aim of the philosopher, is the Good. In his Idea of the Good, Plato envisages an absolute source of truth and goodness. Plato compares this to the sun. As the light of the sun makes the concrete things of the world visible, and is the source of life, the Idea of the Good makes the forms intelligible and is the source of their being. Seen in the light of the Good, the plurality of the many forms becomes the unity of total reality. The Idea of the Good is the source of the world's moral purpose. Such ideas were easily incorporated into later Christian thinking.