Parmenides of Elea (ca. 520 BC - ca. 450 BC) was a Greek
Presocratic philosopher. He was the founder of the Eleatic
school (Some scholars think that his teacher Xenophanes of
Colophon (born about 570 BC), the father of pantheism, was the
real founder). Plato acknowledged that he had magnificent
depths; Plato also named one of his dialogs with his name.
Parmenidean idea of the nature of reality would become the basis
of Plato's thinking.  Through Plato, Parmenides' thoughts
influenced all western philosophy. Some of Parmenides's
arguments are set out in his poem entitled "On Nature", where
"thought and knowledge encounter themselves head on for the
first time". A fragment of this poem says: "That which is not,
is not. "What-is-not" does not exist. Since anything that comes
into being must arise out of what-is-not, objects, states of
affairs and so on cannot come into being. Likewise, they cannot
pass away, because in order to do so they would have to enter
the realm of what-is-not. Since it does not exist, wha