We’ve already talked about the natural philosopher Thales (c. 624-546 BCE), who reasoned that water was the source of all. Coming out of that monistic tradition, we have two natural philosophers who set the stage for Platonic philosophy, posing some of the preliminary questions that Socrates and Plato are going to grapple with: Heraclitus of Ephesus (fl. 504-501 BCE) and Parmenides of Elea (fl. 501-492 BCE).

Heraclitus was from Ephesus, a city that Christians might recognize from the book Ephesians of the New Testament. It is on the west coast of Asia Minor in modern-day Turkey. He came from an aristocratic family but apparently gave up a comfortable life, refusing to participate in local government and instead devoting his time to philosophy while living simply off the land. About 100 fragments of his work are extant, and they, for the most part, come down to us indirectly. That is, throughout the work of other philosophers, we have people who report what Heraclitus wrote. We are entirely dependent on later quotations, paraphrases, and secondhand reports for our understanding of Heraclitus’s philosophical project.

For Heraclitus, the world has always existed. It did not come into being; it did not need to be created. The main problem that Heraclitus spent time on was the problem of change. To him, change is constant and universal. The three themes that span the fragments we have are flux, fire, and the cosmic unity of opposites. He wrote, “This world-order … always was and is and shall be: an ever-living fire, kindling in measures and going out in measures.” Aristotle viewed Heraclitus as a material monist who understood the source of all things as fire. For Heraclitus, fire was both the prime matter of the universe as well as its form. Fire was the Logos incarnate, the material enactment of the principle of change and flux.

Heraclitus called the underlying structure of the universe “the Logos,” and that is the thing that remains constant beneath constant change and flux. In many regards, we can understand Heraclitus as an empiricist: he saw and experienced everything changing, people growing old and dying, the seasons coming and going. He wrote, “I prefer whatever comes from sight, hearing, and learning from experience.” But beneath such change, an eternal logical structure existed: perhaps you’ve heard the expression, “the only constant thing is change.” That type of paradox would appeal to Heraclitus, who was fond of the way in which opposites fit together into a larger, more logical form. He wrote, “It is wise … to agree that all things are one,” and, “Thinking is shared by all.” As part of how he maps the paradox of reality, we have such fragments as, “The beginning and the end are shared in the circumference of a circle,” and, “The way up and down is one and the same.”

His philosophy of constant change can be read in such fragments as, “The sun is new every day,” and, “One cannot step twice into the same river.” Not only has the water in the river changed, but the person doing the stepping has changed as well. Heraclitus also wrote on war: “One must realize that war is shared and Conflict is Justice, and that all things come to pass in accordance with conflict,” and, “War is the father of all and king of all.”