Heraclitus (~500 BCE) was one of the most influential Pre-Socratic philosophers. Along with Parmenides, he's considered the inventor of Western metaphysics.
Plato characterized Heraclitus as the philosopher who posited that existence is pure flux ("No man ever steps into the same
river twice") which was later taken up by relativists and sophists in confounding ways (E.G., "if all is flux, then there is no backdrop of truth, and man is the measure of all things"). But reading the fragments, we may also read him as presenting an uniquely rational philosophy based on an underlying logic in nature, which he identifies with fire.
What can this mean? Is it coherent to say there is a stable ambiguity in nature itself? Can we understand a picture of the world as standing in vitalizing antagonism with itself? How does the "one" relate to the "many"? What is the unity of opposites?
We have only fragments to work with, which allows for (and requires) our own creativity and insights to be brought to the table if we are to fill in the picture.
A good translation that includes the context of the other author in which the fragment occurred can be read here. Another version with the greek can be found here ( more literal, but sometimes less to the point).
Librivox offers a recording of all the fragments read aloud here.
Optional listening also includes episodes 5 and 6 of the Philosophy Without Any Gaps podcast or this discussion featuring three scholars on BBC’s “In Our Time” podcast.
This should be a good time - we will read together live.