The Republic - pg. 196

"... At all events, this is the way the phenomena look to
me: in the knowable the last thing to be seen, that with
considerable effort, is the ideaof the good; but once
seen, it must be concluded that this is in fact the cause of
all that is right and fair in everything - in the visible it gave
birth to light and its sovereign; in the intelligible, itself
sovereign, it provided truth and intelligence - and that the
man who is going to act prudently in private or in public must see it."