cockroaches, he imagined that the earth was filled with tiny invisible “life-
germs.” One thing is certain—he was not talking about Homer’s gods.
The next philosopher we hear of is Anaximander, who also lived in
Miletus at about the same time as Thales. He thought that our world was only
one of a myriad of worlds that evolve and dissolve in something he called the
boundless. It is not so easy to explain what he meant by the boundless, but it
seems clear that he was not thinking of a known substance in the way that
Thales had envisaged. Perhaps he meant that the substance which is the
source of all things had to be something other than the things created.
Because all created things are limited, that which comes before and after
them must be “boundless.” It is clear that this basic stuff could not be anything
as ordinary as water.
A third philosopher from Miletus was Anaximenes (c. 570—526 B.C.).
He thought that the source of all things must be “air” or “vapor.” Anaximenes
was of course familiar with Tholes’ theory of water. But where does water
come from? Anaximenes thought that water was condensed air. We observe
that when it rains, water is pressed from the air. When water is pressed even
more, it becomes earth, he thought. He may have seen how earth and sand
were pressed out of melting ice. He also thought that fire was rarefied air.
According to Anaximenes, air was therefore the origin of earth, water, and fire.
It is not a far cry from water to the fruit of the earth. Perhaps
Anaximenes thought that earth, air, and fire were all necessary to the creation
of life, but that the source of all things was air or vapor. So, like Thales, he
thought that there must be an underlying substance that is the source of all
natural change.
Nothing Can Come from Nothing
These three Milesian philosophers all believed in the existence of a
single basic substance as the source of all things. But how could one
substance suddenly change into something else? We can call this the
problem of change.
From about 500 B.C., there was a group of philosophers in the Greek
colony of Elea in Southern Italy. These “Eleatics” were interested in this
question.
The most important of these philosophers was Parmenides (c. 540-480
B.C.). Parmenides thought that everything that exists had always existed. This
idea was not alien to the Greeks. They took it more or less for granted that
everything that existed in the world was everlasting. Nothing can come out of
nothing, thought Parmenides. And nothing that exists can become nothing.
But Parmenides took the idea further. He thought that there was no such
thing as actual change. Nothing could become anything other than it was.
Parmenides realized, of course, that nature is in a constant state of flux.
He perceived with his senses that things changed. But he could not equate
this with what his reason told him. When forced to choose between relying ei-
ther on his senses or his reason, he chose reason.
You know the expression “I’ll believe it when I see it.” But Parmenides
didn’t even believe things when he saw them. He believed that our senses
give us an incorrect picture of the world, a picture that does not tally with our
reason. As a philosopher, he saw it as his task to expose all forms of
perceptual illusion.