The inquiries of the early dialogues lead naturally to Plato's view of knowledge. Plato distinguishes between opinion and knowledge. One might look at figures like Euthyphro, Laches, and some of the other main characters in the early dialogues as having opinions about piety, courage, and other qualities. Opinion about some matter is not the same as ignorance. But it is not philosophical insight either. Opinion is most people's state of mind. Euthyphro has seen pious actions but does not know what piety is. Laches knows soldiers who are courageous but cannot rise to the more philosophically challenging task of defining courage. You might have seen a beautiful work of art or looked at a person and proclaimed him to be beautiful. But you lack the philosophical acumen to define beauty in its essence. Why is this?

The Allegory of the Cave: Different Levels of Knowledge

Plato makes use of a symbolic story to explain ignorance. In the allegory of the cave the prisoners have been chained in a cave since childhood. They are chained by their necks and can only view the wall of a cave right in front of them. Behind them is a fire and other people. The fire casts shadows on the wall before the prisoners, but the prisoners can never see those people or other objects causing the shadows; they know only the shadows.

Imagine that one of the chained persons was set free from his chains and forced to walk toward the fire, past the objects whose shadows he had just seen, and up to the sunlight coming from outside the cave. His eyes, which had been fixed on shadows only, would be unfamiliar with these new sights. He would rather return to his comfortable world of shadowy images on a wall. After a time, however, he would understand that he was looking at the real objects, not just shadows of things and that the sun illuminated these objects. He would understand that the shadows he had previously seen on the wall did not possess the reality of the objects themselves.

But if he was forced down into the cave again and instructed to tell his fellow prisoners what he had seen, they would mock him and think that he was lying or deranged. He might persuade them to come up and see as he had, but he might not be successful in liberating them, for they would be comfortable where they were. Plato says that they might kill him for even trying to free them and show them the truer nature of things.

Plato's symbolic story suggests that most people dwell in the darkness of the cave, happy to live in a world of shadows and appearances, like the kind found on television. They might take the artificial world of fleeting images to be a world of reality, but it is not. Until they turn their eyes toward the fullest reality — symbolized by the light of the sun illuminating the world outside the cave — they will not have a true education. For those liberated from the cave, the highest knowledge is attainable by contemlation. But they cannot remain in such a state. They must come down and educate the others. Plato was convinced that persons could discover a higher reality.

The Divided Line

Plato's Divided Line corresponds with his allegory of the cave. The line symbolizes different levels of being and the mental faculties used to know them. As such, the divided line is a metaphysical and epistemological affair: it lays out four levels of reality and four faculties used to know those realities. The four levels of being are images, objects, mathematical objects, and forms. The faculties used to know them are imagining, belief, thinking, and understanding.

Let's look at examples of each. Images are the tools of artists and poets. The artist who does a watercolor painting of the Empire State Building doesn't capture the reality of the building itself, but presents an image of the object. In creating that image — which has no more reality than the shadow the prisoners see on the cave wall — he uses his imagination. His created image of the building is a level removed — and a level lower — than the actual brick and steel structure standing in New York. We recognize that structure with our senses, especially sight. These two levels and the faculties utilized to know them are in the realm of opinion.

The realm of knowledge does not depend upon sense knowledge. In the realm of knowledge the faculties employed to know things are thinking and reasoning. At the level of thinking, the thinker employs mathematical hypotheses to understand the Empire State Building. One application is that an engineer or architect looks at a building differently than an ordinary citizen does.

But applied and pure mathematics were not the highest levels of reality. Plato thought that the highest level of reality was the world of ideas or forms.

The forms are pure ideas. Applied to objects like the Empire State Building, the forms are a higher level than the object itself, a pure idea of what the essence of a skyscraper is. Only the highest intelligence can grasp reality at this level. Here understanding works on pure ideas alone, not objects. At this level, a person looking at a beautiful tree or understanding a just action is no longer thinking of those particular things alone.

Understanding is the activity of the philosopher who is thinking of the true nature of beauty or justice in itself. Here one doesn't contemplate holy or courageous or self-controlled persons or actions, but the form or nature of those concepts.