PLATO'S PURE IDEAS
The Peloponnesian War ended after almost thirty years with Sparta's victory in 404 B.C.
Spartans ruled until defeated by Thebes in 371. In 359 Philip II became king of Macedon; in 338
he subjugated Greece, and in 336 he was assassinated and his son Alexander the Great succeeded
Amid this turmoil, philosophy continued. A handsome youth born to a wealthy family, Plato (c.
427-337) was called by that name because of his broad shoulders. His writings fall into two
distinct periods. Duhring the first, he was essentially reporting the teachings of Socrates. After
Socrates' death he left Athens for southern Italy and studied with the Pythagoreans. Pythagoras
(c. 580-500 B.C.), best known as a mathematician, believed that everything in the universe could
be explained in terms of numbers and numberical relationships. He noticed, for instance, that
when one string on a lyre is exactly twice as long as another and they are both played, a pleasant
The Pythagoreans, writes Hergenhahn(p. 31), "assumed a dualistic universe: One part abstract,
permanent, and intellectually knowable, and the other empirical, changing, and known through
the senses." They held that the sensory interferes with the attainment of true knowledge, and
should be avoided --in other words, direct experience is inferior to reasoning as a source of
Plato's own views, as they developed, owe at least as much to the Pythagoreans as to Socrates.
Perhaps more. When in 387 Plato returned to Athens, he based his Academy (after which all
subsequent "academies" are named) on Pythagorean precepts, placing a sign "Let no one without
an understanding of mathematics enter here" above its entrance. His famous allegory which
likened us to people in a cave who can see only shadows of the realities above referred to a
world of enduring, unchanging "pure ideas" or "forms" which our perceptions and
understandings can only approximate. A "form," he held, exists in its own right. I may deal with
several thousand "triangles" in my life, for example, but none is the ideal "Triangle" with exists