The early Greek thinkers clearly made an important break from mythological thinking in the sixth century BC.  Instead of getting their understanding of the world from traditions and imaginative poetic narratives that explained events as resulting from interventions by the gods, they began to look for rational explanations based on natural processes.  They still tended to see the world in terms presented by mythology, for instance viewing the earth as a disk with dry land at the center and an ocean flowing around its edges, as portrayed in the poems of Homer and Hesiod.  But they quickly began to question even the most basic assumptions they had inherited and offered innovative and sometimes insightful alternatives to the traditional worldview. 

The earliest philosophers focused on big questions such as how the world arose and attained its present, more-or-less stable configuration.  Instead of a “theogony” consisting of a genealogy of the gods, some of whom represented parts of the world, such as Gaia, mother Earth, and Ouranos, the god of Heaven, they offered a “cosmogony,” a rational account of how the elements of the world emerged and interacted to produced the heavens, the earth, the seas, and plants, animals, and humans.  They typically offered a “cosmography,” a representation of the structure and shape of the world, and a “cosmology,” an account of how nature maintains a balance between summer and winter, day and night, wet and dry. 

The philosophers’ accounts of the world provided creative interpretations of nature and drew on observed phenomena as evidence for their theories.  Yet they offered competing interpretations of basic phenomena such as seasons and motions of heavenly bodies, as well as of dramatic events such as storms, earthquakes, and eclipses.  For the most part, they failed to develop any consensus about how nature worked, and continued to produce attractive but unverifiable theories of nature.  The philosophers were clearly aiming at a scientific understanding of the world while lacking a reliable methodology, such as experimental methods and controls.  Accordingly, their efforts have been sometimes praised enthusiastically and sometimes dismissed as hopeless by scholars.

As I studied the Presocratic philosophers I came to believe that they did make progress in their explanations, though chiefly at first a kind of theoretical and philosophical progress in clarifying their concepts and developing plausible models, as I argued in my book Explaining the Cosmos.  But I came to see that, far from offering merely speculative hypotheses, some of them contributed to a major breakthrough in astronomy.  Parmenides in particular recognized that the moon must get its light from the sun, for its phases vary with the angular distance between the sun and moon; the moon’s shadows reveal a spherical dark body that reflects sunlight.  Armed with this insight, Anaxagoras was able to explain correctly, for the first time in the history of the world, how eclipses, both solar and lunar, work, based on the blocking of the sun’s light by either the moon or the earth.  This account seems to have been recognized as correct almost immediately, as was established by the fact that from the time of Anaxagoras forward there were no new theories of lunar light or eclipses put forward; instead there arose a consensus that lasted from the early fifth century BC until the present day about lunar light and eclipses.  I have argued for this in my book Science Before Socrates.

What this shows is that the scientific endeavors of the Presocratic philosophers were not in vain.  The scientific attitudes they applied to natural phenomena bore fruit in the early fifth century BC and set astronomy on the path of a science.  By the fourth century BC, Aristotle could hail the explanations of lunar light and eclipses as a paradigm of scientific method, and go on to prove by sound arguments that the earth was spherical in shape (a conjecture that Parmenides had earlier put forward, but without proof).  Eventually the Greeks got access to tables of data from Babylonian astronomers that allowed them, like the Babylonians, to predict eclipses based on past patterns, so that they were in a position to build a hand-held mechanical computer that could track the motions of the heavenly bodies and predict eclipses, the so-called Antikythera Mechanism, recently deciphered.