Plato's theory of knowledge and form are expressed with three approaches: his allegory of The Cave, his metaphor of the Divided Line and his doctrine The Forms. Each theory is interconnected; one could not be without the other. .
In The Cave, Plato describes a vision of shackled prisoners seated in a dark cave facing the wall. Chained also by their necks, the prisoners can only look forward and see only shadows. These shadows are produced by men, with shapes of objects or men, walking in front of a fire behind the prisoners. Plato states that for the prisoners, reality is only the mere shadows thrown onto the wall. Another vision is releasing a prisoner from his chains, how his movements are difficult, his eye adjustment painful and suggestions of the effects of returning to the cave. The Cave suggests to us that Plato saw most of humanity living in "the cave", in the dark, and that the vision of knowledge and the "conversion" to that knowledge was salvation from darkness. He put it this way, "the conversion of the soul is not to put the power of sight in the soul's eye, which already has it, but to insure that, insisted of looking in the wrong direction it is turned the way it ought to be." Plato's two worlds: the dark, the cave, and the bright were his way of rejecting the Sophists, who found "true knowledge" impossible because of constant change. Plato believed there was a "true Idea of Justice". The Cave showed us this. .
The Divided Line visualizes the levels of knowledge in a more systematic way. Plato states there are four stages of knowledge development: Imagining, Belief, Thinking, and Perfect Intelligence. Imagining is at the lowest level of this developmental ladder. Imagining, here in Plato's world, is not taken at its conventional level but of appearances seen as "true reality". Plato considered shadows, art and poetry, especially rhetoric, deceptive illusions, what you see is not necessarily what you get.