Greek Philosophers Formulate Theories of the Cosmos Summary

  • Last updated on November 11, 2022

In Greece, the presocratic philosophers formulated theories of the cosmos, setting aside previous mythopoeic explanations and launching an empirical and scientific intellectual revolution.

Summary of Event

Before the sixth century b.c.e., human beings everywhere explained the world in mythological terms. These myths depicted humankind dependent on the wills of inscrutable gods who created the world and acted on their all-too-human personal whims. Nonliving and powerful natural forces were “animated,” given living souls by the prelogical mentality of early people, otherwise quite sophisticated in building pyramids or irrigation canals. No other explanation was available to them, no scientific foundation on which to build a real understanding of the world and nature. Hesiod Thales of Miletus Anaximander Anaximenes of Miletus Xenophanes Pythagoras Heraclitus of Ephesus Parmenides Democritus

Similarly, most Greeks honored the epic poets Homer (early ninth century-late ninth century b.c.e.) and Hesiod as their teachers. Hesiod’s Theogony (c. 700 b.c.e.; English translation, 1728) is the earliest Greek version of the origins of the cosmos. The Greek term kosmos means the organized world order. In Hesiod’s account, the origin of all things was chaos, formless space or yawning watery deep, the opposite of kosmos. In time there emerged, either independently or by sexual union, Gaia (Earth), Tartaros (Hades), Eros (Love), Night, Day, and Aither (upper air), Sea, and Ouranos (Sky), and boundless Okeanos (Ocean). A generation of powerful Titans was engendered, and finally the Olympian gods descended from Ouranos and Gaia.

About 600 b.c.e., in Ionia (western Turkey), a new way of perceiving the world was beginning. Confronted by the confusing mythologies of ancient Near Eastern peoples, their own no better, a handful of Greeks over three generations attempted to explain the origins and components of the seen world without mythology. Their great discovery was that to one seeking knowledge—the philosopher—the world manifests internal order and discernible regularity. Nature can be understood. The world is a kosmos.

From allusions in Homer and Hesiod came hints. The sky was thought to be a metallic hemispheric bowl covering the disk of earth. The lower space immediately above the disk was aër, breathable air; the upper part of the bowl-space was ouranos or aither. Below its surface, the earth’s deep roots reached down to Tartaros, the deepest part of Hades (the underworld realm of the dead), as far below earth as sky is above it. Okeanos, infinitely wide, encircled the disk of earth and was the source of all fresh and salt waters. Such a mixture of the empirical and the imaginative was common to most mythopoeic cosmologies.

Thales of Miletus was the first to rationalize the myths. He conceived the earth-disk as floating on the ocean and held the single substance of the world to be water. His reasoning, according to Aristotle, was that water can be gaseous, liquid, and solid; life requires water; Homer had surrounded the earth by Okeanos. As a unified source of all things, Thales’ choice of water was a good guess, but it begged for alternatives. More important, in reducing multiple things to water, Thales had taken a first step in establishing inductive reasoning (from particular examples to general principles) as a scientific methodology.

Anaximander, companion of Thales, was a polymath: astronomer, geographer, evolutionist, philosopher-cosmologist. It is nearly impossible to do justice to his intellectual achievement. He was the first Greek to write in prose. He said that animal life began in the sea and that humans evolved from other animals. He made the first world map, a circle showing Europe and Asia plus Africa equal in size, all surrounded by ocean. Anaximander’s cosmos was a sphere with a drum-shaped earth floating in space at its center. The sun, stars, and moon revolved around the earth, seen through openings in the metallic dome of the sky.

In place of Thales’ water, Anaximander offered apeiron, an eternal, undefined, and inexhaustible basic stuff from which everything came to be and to which everything returns. It is a sophisticated chaos. Convinced by his own logic, Anaximander imputed an ethical necessity to this process. Things coming to be and claiming their share of apeiron thus deprive others of existence. So, in his words, “they must render atonement each to the other according to the ordinances of Time.” This eternal process operates throughout the cosmos. Using terms such as kosmos (order), diké (justice), and tisis (retribution), Anaximander enunciated the exalted idea that nature itself is subject to universal moral laws.

The contributions of Anaximenes of Miletus pale before those of Anaximander. What best defines Anaximenes is his empirical approach. He posited air as the primal stuff that gives rise to all things. Observing air condensing into water, he conceived a maximum condensation of air into stone. Similarly, by rarefaction, air becomes fire or soul. The earth and other heavenly bodies, being flat, ride on air in its constant motion.

Xenophanes, an Ionian who had moved to Italy, represents a new generation of thinkers. He interpreted the new natural explanations of the universe that had challenged the older Hesiodic mythopoeic construct as the abandonment of the old, often immoral, anthropomorphic gods, who dressed in clothes and spoke Greek. He posited a single spiritual creator god who controls the universe without effort, by pure thought. In this monotheism, he was alone among the Greeks.

Insightfully, Xenophanes said human knowledge about the universe is limited and the whole truth may never be known. He taught that natural events have natural, not divine, causes. The rainbow is only a colored cloud. The sea is the source of all waters, winds, and clouds. From sea fossils found in rocks, his cosmogony deduced a time when land was under water. Civilization was the work of men, not gods. Xenophanes was a skeptic who trusted only his own observations about the world.

Pythagoras, an Ionian mathematician in southern Italy, had noticed that the sounds of lyre strings varied according to their length and that harmonies were mathematically related. He saw that proportion can be visually perceived in geometrical figures. From these notions he and his followers described a cosmos structured on a mathematical model. Instead of adopting Anaximander’s “justice” or Heraclitus of Ephesus’s logos as the dominant organizing principle, the Pythagoreans preferred numerical harmony. Pythagoras thus added a dimension to the ancient concepts of due proportion and the golden mean that pervaded Greek thought. These concepts are seen in Greek sculpture and architecture and as moral principles in lyric and dramatic poetry and historical interpretations, where hybris (excess) and sophrosyné (moderation) were fundamental principles of human behavior.

Inevitably, Greek physical philosophy began to investigate the process of knowing. Number is unchanging; ten is always ten. In a world of apparently infinite diversity and flux, numbers can be known more perfectly than other objects of experience. Though the Pythagoreans went too far in trying to explain everything by numbers, they taught that a nature based on mathematical harmony and proportion was knowable.

Heraclitus argued that change, though sometimes imperceptible, is the common element in all things. All change, he said, takes place along continuums of opposite qualities, such as the hot-cold line or dry-moist line. His contribution, however, was his idea of logos as the hidden organizing principle of the cosmos. Logos maintains a protective balance (the golden mean again) among all the oppositional tensions in the world.

Although Parmenides and Democritus fall outside the chronological scope of the sixth century b.c.e., their contributions of logic to the Greek discovery of the cosmos merit some attention. In the mid-fifth century, Democritus reasoned to a world built of the smallest thinkable indivisible particles, atoms. Parmenides—struck by the constant flux of the physical world and seeking, as Pythagoras, an unchanging object of knowledge that mind can grasp—saw existence, or Being, as the common element of things in the cosmos. He proposed the logic that while things change, Being itself cannot change, for nothing and no place exists outside of the sphere of Being, so nothing could enter or leave. He is thus the most metaphysical of the philosophers, initiating ideas that would only be completed by Plato and Aristotle, the greatest of the philosophers.


The significance of the Ionian philosophers is that, within little more than a century after breaking with mythopoeic interpretations of the world, they had asserted its atomic makeup, conceived human evolution, discovered induction and logic, and practiced a curiosity about all natural phenomena. This was one of history’s great intellectual revolutions, the origins of scientific speculation.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Kirk, G. S., and J. E. Raven. The Presocratic Philosophers. 2d ed. New York: Cambridge University Press, 1984. A collection of Greek texts and English translations, with commentary based upon the words of individual philosophers.
  • citation-type="booksimple"

    xlink:type="simple">Long, A. A. The Cambridge Companion to Early Greek Philosophy. New York: Cambridge University Press, 1999. Includes essays on both individual philosophers and overarching themes.
  • citation-type="booksimple"

    xlink:type="simple">Morgan, Kathryn A. Myth and Philosophy from the Presocratics to Plato. New York: Cambridge University Press, 2000. Explores the interactions between mythological and scientific thinking in classical Greece culture.
  • citation-type="booksimple"

    xlink:type="simple">Popper, Karl R. The World of Parmenides: Essays on the Presocratic Enlightenment. Edited by Arne F. Petersen and Jørgen Mejer. New York: Routledge, 1998. One of the most influential philosophers of the twentieth century assesses the work and worldview of the Presocratics, focusing on Parmenides. The essays attempt to illuminate the ways in which Presocratic philosophy still guides modern conceptions of the scientific process.
  • citation-type="booksimple"

    xlink:type="simple">Ring, Merrill. Beginning with the Presocratics. 2d ed. New York: McGraw-Hill, 1999. A short and accessible introduction to the Presocratic philosophers, intended as an introductory college text.
  • citation-type="booksimple"

    xlink:type="simple">Wakefield, Robin, ed. The First Philosophers: The Presocratics and the Sophists. New York: Oxford University Press, 2000. A collection of translations of the important Presocratic philosophers, including Thales, Anaximander, Anaximenes of Miletus, Heraclitus of Ephesus, Xenophanes, and Parmenides. Textual and explanatory notes, chronology, bibliography, concordance, and index.
Related Articles in <i>Great Lives from History: Ancient World</i>

Anaximander; Anaximenes of Miletus; Aristotle; Democritus; Heraclitus of Ephesus; Hesiod; Parmenides; Plato; Pythagoras; Socrates; Thales of Miletus; Xenophanes. Philosophy;Greece Cosmology, Greek

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