Pre-Socratic Philosophers: A Summary of the Search for the Arché

In the sixth century BC, in the Greek cities on the coast of Asia Minor, a group of thinkers starts asking a new kind of question: what does everything that exists derive from? It is a question about nature, pursued through reasoned argument. According to the Stanford Encyclopedia of Philosophy, these philosophers — who were active across the sixth and fifth centuries BC — open up a fresh way of questioning nature and our own place within it. We call them “pre-socratics” because they lived before Socrates, even though the label is not strictly chronological: the last of them were contemporaries of Socrates himself, and even of Plato. It fits better as a school of thought than as a spot on the timeline. These cities belonged to the world of the Greek poleis, where the same period also saw the first forms of participatory government.

Thales, water as the principle

Born in Miletus, a Greek city in Ionia, Thales was, according to Aristotle’s testimony, the first to search for the first cause of everything, and he identified it with water. For him water was the arché, the basic principle everything originates from. According to the Internet Encyclopedia of Philosophy, by explaining natural phenomena through material causes, Thales opened a path different from traditional mythological explanations, which is why he is considered the founder of Greek natural philosophy.

Anaximander, the boundless apeiron

Anaximander, active in Miletus from around 610 to 546 BC, is credited with the oldest surviving lines of Western philosophy. The same source calls him the first to have dared to write a treatise in prose rather than in verse, traditionally titled On Nature — a work now lost. Anaximander explicitly ruled out water or any other known element as the principle of everything: he called it apeiron, the boundless, the unbounded, something with no limits and no specific nature of its own. Even in antiquity, the source notes, people complained that Anaximander had never explained precisely what he meant by the boundless — an ambiguity already present in the original text. Thales reached for a substance he could point to; Anaximander reached past every known substance, toward something without a shape at all.

Anaximander is also credited with some of the earliest Greek astronomical ideas: he held that the earth floats freely at the center of the universe, with no support underneath it — no water, no pillars — and he was the first to picture the heavenly bodies arranged at different depths, one behind the other.

Anaximenes of Miletus, air that transforms

Anaximenes of Miletus was active in the middle of the sixth century BC and died around 528 BC: he is the third philosopher of the school of Miletus, after Thales and Anaximander. According to Theophrastus’s testimony, reported by the Internet Encyclopedia of Philosophy, he was linked to Anaximander and perhaps his student. His own mark on the school’s question is the claim that air, found everywhere, underlies everything that exists.

Anaximenes described a precise mechanism of transformation: air that is thinned out, rarefied, becomes fire; condensed step by step it becomes wind, then cloud, then water, then earth, finally stone.

Practical example: to show the link between rarefaction, condensation and temperature, Anaximenes pointed to a concrete, everyday observation: blowing with an open mouth produces warm air, because it is rarefied; blowing with pursed lips produces cold air, because it is dense. A small daily experiment used to support a theory about the origin of everything.

Heraclitus of Ephesus and the ever-living fire

Heraclitus was a Greek philosopher from Ephesus, near present-day Kuşadası, in Turkey, active around 500 BC. According to the Stanford Encyclopedia of Philosophy, he wrote in fragments with an intentional syntactic ambiguity, a technique that brings his words close, in verbal complexity, to poetry. For Heraclitus, the order of the world is an ever-living fire, created by no god and no human being, which always was, is and will be. He pointed listeners toward the Logos, the rational law running through everything: in a deep sense, he said, all things are one.

In his most quoted fragment, Heraclitus observes that different waters flow upon those who step into the same rivers: the classic image of constant change, which later gave rise to the phrase panta rhei, everything flows. He also held that opposites are one and the same in us — living and dying, waking and sleeping, youth and old age — because each one turns continuously into the other.

Pythagoras and the Pythagorean community

Pythagoras lived roughly from 570 to 490 BC — the Stanford Encyclopedia of Philosophy uses “about” because the exact dates stay uncertain. He spread an optimistic view of the soul’s fate after death, immortal and subject to a series of reincarnations, and founded a way of life people found attractive for its rigor and discipline: the Pythagorean community. Historically his fame rested mainly on this doctrine of the soul, rather than on mathematics: the oldest testimonies do not show Pythagoras’s fame resting mainly on numbers or cosmology, and whether he himself worked on rational cosmology remains a matter of academic debate.

It was mainly with his followers in the Pythagorean tradition, Philolaus and Archytas, that the view of the cosmos turned toward science and mathematics, with numerical relationships at the heart of how the cosmos was structured. Readers who want to see where that direction leads, a few centuries later, can read the Recap on Euclidean geometry, with the postulates and theorems of the Elements.

Parmenides of Elea and unmoving Being

Parmenides of Elea, active in the early part of the fifth century BC, wrote a single metaphysical poem — according to the ancient testimony of Diogenes Laertius — and the Stanford Encyclopedia of Philosophy calls him the most profound and challenging thinker of early Greek philosophy. In the poem, written in hexameters, the form of Greek epic poetry, a goddess describes two paths of inquiry: the first, that something is and cannot possibly not be, is the path of conviction, because it rests on true reality; the second, that something is not and must not be, is a path with no possibility of knowledge at all.

For Parmenides, it is necessary to say and think that Being is, because it is possible for it to be, while non-being cannot in any way be thought or said. This is why Being is eternal and unmoving: in true reality there is no birth and no death, and no motion is possible. The need to explain reality from a small set of basic principles does not end with the pre-socratics: the same approach, applied to a different object, numbers, underlies arithmetic and its foundations.