Delahoyde & Hughes
The Greeks invented this too, in the 6th century BCE according to tradition. Presocratic philosophers or thinkers started seeing the world not as something random and arbitrary, but "as something ordered and intelligible, its history following an explicable course and its different parts arranged in a comprehensible system" (Barnes xviii). Eventually, in this early history of philosophy, reasoned argumentation became the way to the truth.
None of the presocratic works have survived intact, so that we rely on fragments, mostly quotations in other early texts of varying reliability. But presocratic philosophers worth a glance are: Thales (whom Aristotle considered "the founder of natural philosophy"), Anaximander (who considered all things to be made of the same element, or archê), Anaximenes (who thought all substance to be air, rarified or condensed), Alcmaeon (a pupil of Pythagoras and a physician), Xenophanes (a wandering poet), Empedocles (who argued that the universe consists of four elements: earth, air, fire, and water), Anaxagoras (who "held that the original cosmogonical force was mind or thought"), and the major philosophers listed below.Heraclitus
Barnes, Jonathan. Early Greek Philosophers. NY: Penguin, 2001.
Orpheus: Greek Innovations