This unshakable faith in human reason is called rationalism. A rationalist
is someone who believes that human reason is the primary source of our
knowledge of the world.
All Things Flow
A contemporary of Parmenides was Heraditus (c. 540-480 B.C.), who
was from Ephesus in Asia Minor. He thought that constant change, or flow,
was in fact the mosf basic characteristic of nature. We could perhaps say that
Heraclitus had more faith in what he could perceive than Parmenides did.
“Everything flows,” said Heraclitus. Everything is in constant flux and
movement, nothing is abiding. Therefore we “cannot step twice into the same
river.” When I step into the river for the second time, neither I nor the river are
the same.
Heraclitus pointed out that the world is characterized by opposites. If we
were never ill, we would not know what it was to be well. If we never knew
hunger, we would take no pleasure in being full. If there were never any war,
we would not appreciate peace. And if there were no winter, we would never
see the spring.
Both good and bad have their inevitable place in the order of things,
Heraclitus believed. Without this constant interplay of opposites the world
would cease to exist.
“God is day and night, winter and summer, war and peace, hunger and
satiety,” he said. He used the term “God,” but he was clearly not referring to
the gods of the mythology. To Heraclitus, God—or the Deity—was something
that embraced the whole world. Indeed, God can be seen most clearly in the
constant transformations and contrasts of nature.
Instead of the term “God,” Heraclitus often used the Greek word logos,
meaning reason. Although we humans do not always think alike or have the
same degree of reason, Heraclitus believed that there must be a kind of
“universal reason” guiding everything that happens in nature.
This “universal reason” or “universal law” is something common to us all,
and something that everybody is guided by. And yet most people live by their
individual reason, thought Heraclitus. In general, he despised his fellow be-
ings. “The opinions of most people,” he said, “are like the playthings of
infants.”
So in the midst of all nature’s constant flux and oppo-sites, Heraclitus
saw an Entity or one-ness. This “something,” which was the source of
everything, he called God or logos.
Four Basic Elements
In one way, Parmenides and Heraclitus were the direct opposite of each
other. Parmenides’ reason made it clear that nothing could change.
Heraclitus’ sense perceptions made it equally clear that nature was in a
constant state of change. Which of them was right? Should we let reason
dictate or should we rely on our senses?
Parmenides and Heraclitus both say two things:
Parmenides says:
a) that nothing can change, and
b) that our sensory perceptions must therefore be unreliable. Heraclitus,