The Republic - pg. 295

"... But it must be seen such as it is in truth, not maimed
by community with body and other evils, as we now see it.
But what it is like when it has become pure must be examined
sufficiently by calculation. And one will find it far fairer and
discern justice and injustice and everything we have now
gone through more distinctly. Now we were telling the truth
about it as it looks at present. However that is based only
on the condition in which we saw it. Just as those who
catch sight of the sea Glucon would no longer easily see his
original nature because some of the old parts of his body have
been broken off and the others have been ground down and
thoroughly maimed by the waves at the same time as other
things have grown on him - shell, seaweed, and rocks - so
that he resembles any beast rather than what he was by
nature, so, too, we see the soul in such a condition because
of countless evils. But, Glaucon, one must look elsewhere."