Plato
Book VII of  The Republic

The Allegory of the Cave

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[Socrates:]  And now, I said, let me show in a figure how far our nature is
enlightened or unenlightened: --Behold! human beings living in a
underground den, which has a mouth open towards the light and
reaching all along the den; here they have been from their childhood, and
have their legs and necks chained so that they cannot move, and can only
see before them, being prevented by the chains from turning round their
heads. Above and behind them a fire is blazing at a distance, and between
the fire and the prisoners there is a raised way; and you will see, if you
look, a low wall built along the way, like the screen which marionette
players have in front of them, over which they show the puppets.
...
And do you see, I said, men passing along the wall carrying all sorts of
vessels, and statues and figures of animals made of wood and stone and
various materials, which appear over the wall? Some of them are talking,
others silent. .
...
Like ourselves, I replied; and they see only their own shadows, or the
shadows of one another, which the fire throws on the opposite wall of the
cave?  
...
And if they were able to converse with one another, would they not suppose
that they were naming what was actually before them?
...
And suppose further that the prison had an echo which came from the
other side, would they not be sure to fancy when one of the passers-by
spoke that the voice which they heard came from the passing shadow?
...
To them, I said, the truth would be literally nothing but the shadows of the
images.
...
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From http://classics.mit.edu/Plato/republic.html
What is an
underground
den?
A Cave
Marionette
Players:

Individuals
who
manipulate
puppets with a
set of strings
What are
shadows?

Regions of
darkness where
light is blocked
What is the main
point of this text?

If people don't see
things correctly
they may not
even know it.  For,
how could they
know it?
Does Plato only
care about how
people see things?
 

No, he is
concerned with
the nature of truth.

How can you
actually know
whether or not you
know the truth?
I can't help but wonder if today everybody only sees through shadows.  The greatest problem is that
shadows differ, depending on where the person views it from.  Therefore we often view things differently
from one another.  Viewing things differently causes people to hurt one another.  Until we come out of the
cave we will continue to see things differently.  A key question is how do we push people out of the cave?   
How do we push ourselves out of the cave?
Questions for Science:
How do people actually see?
How do shadows actually work?
What would have to happen for all shadows to disappear?