The philosophers observed with their own eyes that nature was in a constant state of transformation. But how could such transformations occur?
How could something change from being substance to being a living thing, for example?
All the earliest philosophers shared the belief that there had to be a certain basic substance at the root of all change. How they arrived at this idea is hard to say. We only know that the notion gradually evolved that there must be a basic substance that was the hidden cause of all changes in nature. There had to be "something" that all things came from and returned to.
For us, the most interesting part is actually not what solutions these earliest philosophers arrived at, but which questions they asked and what type of answer they were looking for. We are more interested in how they thought than in exactly what they thought.
We know that they posed questions relating to the transformations they could observe in the physical world. They were looking for the underlying laws of nature. They wanted to understand what was happening around them without having to turn to the ancient myths. And most important, they wanted to understand the actual processes by studying nature itself. This was quite different from explaining thunder and lightning or winter and spring by telling stories about the gods.
So philosophy gradually liberated itself from religion. We could say that the natural philosophers took the first step in the direction of scientific reasoning, thereby becoming the precursors of what was to become science.
Only fragments have survived of what the natural philosophers said and wrote. What little we know is found in the writings of Aristotle, who lived two centuries later. He refers only to the conclusions the philosophers reached. So we do not always know by what paths they reached these conclusions. But what we do know enables us to establish that the earliest Greek philosophers' project concerned the question of a basic constituent substance and the changes in nature.
THREE PHILOSOPHERS FROM MILETUS
The first philosopher we know of is Thales, who came from Miletus, a Greek colony in Asia Minor. He traveled in many countries, including Egypt, where he is said to have calculated the height of a pyramid by measuring its shadow at the precise moment when the length of his own shadow was equal to his height. He is also said to have accurately predicted a solar eclipse in the year 585 B.C.
Thales thought that the source of all things was water. We do not know exactly what he meant by that, he may have believed that all life originated from water--and that all life returns to water again when it dissolves.
During his travels in Egypt he must have observed how the crops began to grow as soon as the floods of the Nile receded from the land areas in the Nile Delta. Perhaps he also noticed that frogs and worms appeared wherever it had just been raining.
It is likely that Thales thought about the way water turns to ice or vapor--and then turns back into water again.
Thales is also supposed to have said that "all things are full of gods." What he meant by that we can only surmise. Perhaps, seeing how the black earth was the source of everything from flowers and crops to insects and 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?