1. The Allegory of the Cave
by ancient Greek philosopher
Plato
( BC)
Is not the dreamer, sleeping or waking, one who likens dissimilar things, who puts the copy in place of the real object?
- Plato

2. Plato
The son of a wealthy and noble family, Plato ( B.C.) was preparing for a career in politics when the trial and eventual execution of Socrates (399 B.C.) changed the course of his life. He abandoned his political career and turned to philosophy, opening a school on the outskirts of Athens dedicated to the Socratic search for wisdom. Plato's school, then known as the Academy, was the first university in western history and operated from 387 B.C. until A.D. 529, when it was closed by the Roman Emperor Justinian.
Plato was both a writer and a teacher. His writings are in the form of dialogues, with Socrates as the principal speaker. This discussion format has become known as Socratic dialogue.

3. Plato’s theory of Forms
The visible world is what surrounds us: what we see, what we hear, what we experience; this visible world is a world of change and uncertainty.
The intelligible world is made up of the unchanging products of human reason: anything arising from reason alone, such as abstract definitions or mathematics, makes up this intelligible world, which is the world of reality.
The intelligible world contains the eternal "Forms" (in Greek, idea ) of things.

4. The visible world is the imperfect and changing manifestation in this world of these unchanging forms. For example, the "Form" or "Idea" of a horse is intelligible, abstract, and applies to all horses; this Form never changes, even though horses vary wildly among themselves—the Form of a horse would never change even if every horse in the world were to vanish. An individual horse is a physical, changing object that can easily cease to be a horse (if, for instance, it's dropped out of a fifty story building); the Form of a horse, or "horseness," never changes. As a physical object, a horse only makes sense in that it can be referred to the "Form" or "Idea" of horseness.
Plato realizes that the general run of humankind can think, and speak, etc., without (so far as they acknowledge) any awareness of his realm of Forms.

5. In The Allegory of the Cave, Plato likens people untutored in the Theory of Forms to prisoners chained in a cave, unable to turn their heads. All they can see is the wall of the cave. Behind them burns a fire.  Between the fire and the prisoners there is a parapet, along which puppeteers can walk. The puppeteers, who are behind the prisoners, hold up puppets that cast shadows on the wall of the cave. The prisoners are unable to see these puppets, the real objects, that pass behind them. What the prisoners see and hear are shadows and echoes cast by objects that they do not see.

7. Such prisoners would mistake appearance for reality
Such prisoners would mistake appearance for reality. They would think the things they see on the wall (the shadows) were real; they would know nothing of the real causes of the shadows.
So when the prisoners talk, what are they talking about? If an object (a book, let us say) is carried past behind them, and it casts a shadow on the wall, and a prisoner says “I see a book,” what is he talking about? He thinks he is talking about a book, but he is really talking about a shadow. But he uses the word “book.” What does that refer to?
Plato’s answer was:
“And if they could talk to one another, don’t you think they’d suppose that the names they used applied to the things they see passing before them?”
Couldn’t it be the same for us, fooled by our senses into thinking that we perceived reality, when in truth it is just a shadow of the intelligible world?

8. Plato’s point is that the prisoners would be mistaken
Plato’s point is that the prisoners would be mistaken. For they would be taking the terms in their language to refer to the shadows that pass before their eyes, rather than (as is correct, in Plato’s view) to the real things that cast the shadows. If a prisoner says “That’s a book” he thinks that the word “book” refers to the very thing he is looking at. But he would be wrong. He’s only looking at a shadow. The real referent of the word “book” he cannot see. To see it, he would have to turn his head around.

9. Plato’s point: the general terms of our language are not “names” of the physical objects that we can see. They are actually names of things that we cannot see, things that we can only grasp with the mind.
The prisoners may learn what a book is by their experience with shadows of books. But they would be mistaken if they thought that the word “book” refers to something that any of them has ever seen.
Likewise, we may acquire concepts by our perceptual experience of physical objects. But we would be mistaken if we thought that the concepts that we grasp were on the same level as the things we perceive.
Suppose now that one of the men escaped, and got out of the cave, and saw what real people looked like, and real trees and grass. If he went back to the cave and told the other men what he had seen, would they believe him, or would they think he was crazy?

10. We can come to grasp the true Forms with our minds.
When the prisoners are released, they can turn their heads and see the real objects. Then they realize their error. What can we do that is analogous to turning our heads and seeing the causes of the shadows?
Plato says that we are like those men sitting in the cave: we think we understand the real world, but because we are trapped in our bodies we can see only the shadows on the wall. One of his goals is to help us understand the real world better, by finding ways to predict or understand the real world even without being able to see it.
We can come to grasp the true Forms with our minds.

11. In conclusion
The Allegory presents, in brief form, most of Plato's major philosophical assumptions: his belief that the world revealed by our senses is not the real world but only a poor copy of it, and that the real world can only be apprehended intellectually; his idea that knowledge cannot be transferred from teacher to student, but rather that education consists in directing student's minds toward what is real and important and allowing them to apprehend it for themselves; his faith that the universe ultimately is good; his conviction that enlightened individuals have an obligation to the rest of society, and that a good society must be one in which the truly wise (the Philosopher-King) are the rulers.
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12. The key knowledge issues for us are:
the world revealed by our senses is not the real world but only a poor copy of it (our sensory organs are limited, but also our mental ability to interpret what the brain receives is limited)
real world can only be apprehended intellectually (in our minds)
this requires active thought: we need to direct our minds toward what is real and important and to apprehend it for ourselves (not be shown)
How valuable is this model of knowledge acquisition?