The Divided Line - Socrates Attempts to Explain the Quest of the Philosopher to Glaucon
In Book VI of the Republic, Socrates attempts to elucidate the nature of philosophy to Glaucon through the image of the Divided Line. Socrates asks Glaucon to imagine two realms: that of the intelligible and that of the visible. He then instructs Glaucon to picture a line which divides these two realms, separating them from each other. Socrates asks Glaucon to divide the visible and the intelligible realm again, so that each realm consists of two parts. These divisions are made to emphasize their ascending causality, clarity, unity, and eternality – their ascent in being.
Images constitute the lower division of the visible realm. They possess less being than the things that cause them and thus contain the least being of all. Things represent the highest level of visibility, for they are the source of images. Things themselves however mean nothing to us if they are not intelligible. When we see a thing, a hammer for example, we do not see a mere conglomeration of visible properties; we do not say to ourselves, “Ah, it is the brown, grey, long, smooth, with at curve at the end thing.” We instead associate these visible properties with the idea of the hammer, the eidos. With the idea, we have ascended above mere things, of which there are many, to a unity. Even if we are to see two hammers, each with completely different visible properties, we are still able to understand that each is a hammer. Thus, ideas unify and allow for myriad things in the visible world to be intelligible to the eyes of the mind.
Just as ideas are sought to make intelligible the many things of the visible world, the philosopher, thirsty for knowledge, seeks the unity of ideas. See seeks idea of these ideas – the One idea in which myriad ideas are made intelligible in their oneness. The philosopher makes it his quest to understand this ultimate cause and unifying principle. Plato calls this the idea of the Good. The Good as the highest unity is thus the ultimate cause of all things in their many forms. The philosopher endlessly pursues the Good, seeking to understand it as the highest unity operating in and behind all things. But will his knowledge ever be satiated?