In book seven of Plato’s The Republic, he tells us about some people chained in a cave, forced to watch shadows across a stone wall.
The group of prisoners has been living there in chains since their birth. They have never seen the outside world, only shadows of it. They have no knowledge of anything beyond their miserable lives in the cave.
The prisoners are chained facing a wall and can’t turn their heads. There’s a fire behind them which produces some light. Occasionally people pass by that fire with animals and objects or figures that are cast in the wall, and the prisoners can see their shadows.
All that the prisoners know are those shadows. They name them and believe they are real entities. They talk about the shadows with enthusiasm and are fascinated by them, thinking that if you pay attention, you can succeed in life.
One day, a prisoner manages to free himself from the chains and step outside the cave to see the outer world. At first, the sun burns his eyes, but then they adjust, and he finds everything so colorful, exciting, full of life. He sees the real forms of the things he knew as shadows, like rabbits, birds, flowers, people, objects, he even sees the sky and stars.
“Previously, he had been looking only at phantoms; now, he is nearer to the true nature of being.” – Plato
People explain to him that everything he sees is real, and the shadows are just mere reflections. Although he cannot understand this at first, he then adjusts and sees how the sun is responsible for light and producing the shadows.
The prisoner gets back to the cave and tells everyone what he had just witnessed, but no one believes him. His eyes had adjusted to the sun, and now he can’t see the shadows clearly as he did before. They tell him he’s crazy, and violently resist while he tries to free them.
The cave signifies ignorance.