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The first school of philosophy. Based in the Ionian city of Miletus, these thinkers sought natural explanations for the world, launching the tradition of rational inquiry. Thales proposed water as the fundamental substance; his successors offered air and the infinite.
Key Idea
Nature has a rational order that can be understood through inquiry.
Part school, part religious community, part political movement. Founded by Pythagoras in Croton, southern Italy. Members lived communally, followed strict dietary rules, and believed that mathematics reveals the deep structure of reality. Their motto: all is number.
Key Idea
Mathematics is the language of the cosmos.
Members
Pythagoras
c. 570 BCE
Based in Elea, southern Italy. Parmenides and his followers argued that change, motion, and multiplicity are illusions. Only Being exists — whole, unchanging, and indivisible. Their radical logic forced every subsequent philosopher to reckon with the problem of reality.
Key Idea
What is, is. What is not, cannot be. Change is impossible.
Democritus and Leucippus proposed that the universe consists of indivisible particles (atoms) moving through empty space. No gods, no design — just atoms and void. Their materialism anticipated modern physics by two thousand years.
Key Idea
Everything is atoms and empty space. All else is opinion.
Members
Democritus
c. 460 BCE
Not a formal school but a method. Socrates taught by questioning, never lecturing. He aimed not to transmit knowledge but to reveal ignorance — including his own. His students went on to found most of the major philosophical schools that followed.
Key Idea
The unexamined life is not worth living.
Founded with Plato's Academy in Athens, the longest-running school in the ancient world. Platonists held that the visible world is a shadow of a higher reality — the realm of eternal Forms. The school evolved through centuries, from Plato's original teachings through Middle and Neoplatonism.
Key Idea
True reality is the invisible world of Forms; what we see is mere appearance.
Members
Plato
c. 428 BCE
Aristotle's school at the Lyceum, named for the covered walkway (peripatos) where he taught. The Peripatetics were empirical, systematic, and wide-ranging — contributing to biology, logic, ethics, politics, and literary criticism. Where Plato looked up to the Forms, Aristotle looked around at the world.
Key Idea
Understanding comes from observation, classification, and careful reasoning.
Diogenes and his followers rejected civilization's comforts and conventions. They lived in deliberate poverty, mocked social norms, and argued that virtue means living according to nature. The word 'cynic' comes from the Greek for 'dog' — and they wore the insult proudly.
Key Idea
Strip away custom, status, and comfort — what remains is freedom.
Members
Diogenes
c. 412 BCE
Epicurus' Garden school taught that pleasure — specifically the absence of pain and anxiety — is the highest good. Do not fear the gods (they are indifferent). Do not fear death (you will not experience it). Live simply, love your friends, and think clearly.
Key Idea
The good life is freedom from fear and the quiet company of friends.
Members
Epicurus
341 BCE
Founded by Zeno of Citium at the Painted Porch in Athens. Stoics taught that virtue is the only true good, that the universe is rational, and that we should align our will with nature. The school became the dominant philosophy of the Roman world, adopted by emperors and enslaved people alike.
Key Idea
Virtue is the sole good. What is not in your control is not your concern.
Members
Zeno of Citium
c. 334 BCE
Pyrrho pioneered radical doubt: since we cannot know the true nature of things, we should suspend judgment entirely. The result is not confusion but tranquility. Later skeptics in Plato's Academy continued the tradition, turning doubt into a philosophical method.
Key Idea
Suspend judgment. Certainty is beyond us, but peace is not.
Members
Pyrrho
c. 365 BCE
